Part 0 basic pharmacology 2013 by Rene NGABOYISONGA

BASIC PHARMACOLOGY PROFESSOR KADIMA NTOKAMUNDA 2013 1

STUDY CONTENT SECTION 1: FUNDAMENTALS OF CLINICAL PHARMACOLOGY Chap 1: INTRODUCTION TO PHARMACOLOGY Chap 2: GENERAL PRINCIPLES OF PHARMACOKINETICS Chap 3: GENERAL PRINCIPLES OF PHARMACODYNAMICS Chap 4: GENERAL PRINCIPLES OF TOXICOLOGY Chap 5: GENERAL PRINCIPLES OF PHARMACOTHERAPY SECTION 2: PHARMACOLOGY OF THE PERIPHERAL NERVOUS SYSTEM

SECTION1 : FUNDAMENTALS OF CLINICAL PHARMACOLOGY • At Home (relatives)

Physician

– Symptoms onset – First intervention – Self-medication!!!

Disease diagnosis Medicine(s) prescribing

• At Hospital (physician) – – – –

Physical Diagnosis Lab tests Disease identification Prescription medicines

Patient

• At Pharmacy (pharmacist)

medicines taking

– Medicines dispensing – Pharmaceutical Care

• At Nursery (nurse) – Medicines administration – Nursing Care

Nurse

Pharmacist

Medicines administration

Medicine(s) dispensing

Patient Care 3

Chapter 1 INTRODUCTION TO PHARMACOLOGY 1. 2. 3. 4.

DEFINITION AND SCOPE OF PHARMACOLOGY HISTORY OF PHARMACOLOGY CHEMICAL PROPERTIES OF DRUGS PHARMACEUTICAL PROPERTIES OF MEDICINES 5. DEVELOPMENT OF NEW MEDICINES

1.1 DEFINITIONS AND SCOPE • What is Pharmacology? – Etymologically ‘pharma’ means ‘drug’ and ‘logy’ means ‘study’; hence pharmacology is defined as the study of drug action. It focuses on how drugs interact within biological systems to affect function. – A very broad definition of pharmacology would include the study of Medicinal chemistry, Pharmacy, Pharmacokinetics, Pharmacodynamics, Toxicology and Pharmacotherapy. 5

DEFINITIONS AND SCOPE What is Drug? • A drug is a chemical that interacts with a living system through biochemical processes, especially by binding to regulatory molecules to affect body function. • If the affect helps the body, the drug is a medicine. If the affect harms the body, the drug is a poison. What is Medicine? • A medicine can be defined as drug delivery system; that is, a medicine is made up of drug mixed with inactive material called “excipient “ or “inactive ingredient”.

Excipients

Drug Medicine

Pharmacy converts drugs into medicines 6

Legal definition of drug or medicine â&#x20AC;˘ The legislator defines drug or medicine as â&#x20AC;&#x153;any synthetic or naturally occurring chemical agent or any preparation other than food that affects physical or psychological functions and may be used to cure, prevent, diagnose diseases, or to restore, correct, or modify a physiological function in humans or in animalsâ&#x20AC;?. Examples Curative drugs Preventive drugs Reliever drugs Diagnose drugs Modifier drugs

Therapeutic class Antibiotics Vaccines Analgesics Contrast products Contraceptives

The scope of pharmacology • At its broadly sense, pharmacology is a multidisciplinary science integrating a number of branches, namely: • Medicinal chemistry: – study of chemical properties of drugs ;

• Pharmacy: – study of drug dosage forms;

• Pharmacokinetics: – study of the action of the body on the drug

• Pharmacodynamics: – study of the action of the drug on the body

• Pharmacotherapy: – study of clinical application of drugs

• Toxicology: – study of harmful action of drugs in the body 8

The scope of pharmacology â&#x20AC;˘ Medical pharmacology is often defined as the science of substances used to prevent, diagnose, and treat diseases. â&#x20AC;˘ Experimental pharmacology is the study of biological and therapeutic properties of new natural or synthetic substances, by testing them systematically on different living systems, using different techniques that are specific to pharmacology or borrowed to physiology and biology. 9

1.2 HISTORY OF PHARMACOLOGY PHARMACIST

PHYSICIAN

PATIENT

Ancient Pharmacology Area • Since the dawn of humankind (prehistoric people) mixtures of animal parts, plants and minerals to treat wounds sores and ailments evolved from rudimentary pharmacological compounds into more sophisticated experiments to create medical treatments. • Egypt first documented herbal amalgams for healing. Archives of ancient Greek texts reveal the extent of their medicinal knowledge of herbal mixtures. • Chinese and Arab peoples advanced pharmacology research of herbal and mineral benefits for medical treatments as well. • Early in the 20th century modern pharmacology emerged with the first synthetic compound created in Europe. 11

HISTORICAL NAMES

•

Hippocrates of Cos or Hippokrates of Kos (Greek: Ἱπποκράτης; Hippokrátēs; ca. 460 BC – ca. 370 BC) was an ancient Greek physician of the Age of Pericles (Classical Athens), and is considered one of the most outstanding figures in the history of medicine.

• He is referred to as the father of Western medicine in recognition of his lasting contributions to the field as the founder of the Hippocratic School of medicine. • This intellectual school revolutionized medicine in ancient Greece, establishing it as a discipline distinct from other fields that it had traditionally been associated with (notably theurgy and philosophy), thus establishing medicine as a profession.

HISTORICAL NAMES •

•

Aelius Galenus or Claudius Galenus (September AD 129 – 199/217; Greek: Γαληνός, Galēnos, from adjective "γαληνός", "calm", better known as Galen of Pergamon (modern-day Bergama, Turkey), was a prominent Roman (of Greek ethnicity) physician, surgeon and philosopher. Arguably the most accomplished of all medical researchers of antiquity.

•

Father of the pharmacy he is the founder of the «polypharmacy» or art to mix several substances to make a medicine of it. To Hippocrates’ body humors theory, Galen advanced this theory, creating a typology of human temperaments adding air, earth, fire, water. An imbalance of each humor corresponded with a particular human temperament (blood-sanguine, black bilemelancholic, yellow bile-choleric, and phlegmphlegmatic). Individuals with sanguine temperaments are extroverted and social. Choleric people have energy, passion and charisma. Galen contributed greatly to the understanding of numerous scientific disciplines including anatomy physiology, pathology, pharmacology, and neurology, as well as philosophy, and logic.

Other Historical paragons Name

Legacy

THEOPHRASTUS (372-287 ave JC.)

Grandfather of the pharmacognosy, wrote the first treaty on the history of the plants.

PARACELSUS (1499-1541) (true name : Philippus Theophrastus Bombastus Hohenheim von)

Revolutionary, he denounced the polypharmacy of Galen to the point to burn the documents of it on the public place. He/it extolled the use of the simple chemical bodies (mercury for the syphilis). He/it is the first to establish the real tie between the chemistry and the medicine: the illness is caused by a disruption of the chemical environment of the organism. He/it didn't succeed however in separating completely the medicine of the religion Initiated the administration of the medicines by intravenous way. He is the first to isolate the morphine: beginning of the phytochemistry. The two contributed to the study of the mechanisms of action of the drugs. He is known for his works on the structure-activity relationship Founder of the first laboratory of experimental pharmacology Great professor of pharmacology, he trained a lot of disciples in the world of who Jacob ABEL father of the American pharmacology. 14

WILLIAM HARVEY (1578 -1657) Frederick W.A. SERTUNER (1743-1841) Franรงois MAGENDIE (1783-1855) and Claude BERNARD (1813-1878) James BLAKE (1815-1893) RUDOLF BUCHHEIM (1820-1879) OSWARD SCHMIEDEBERG (1838-1881)

Experimental Pharmacology Area â&#x20AC;˘ Around the end of the 17th century, reliance on observation and experimentation began to replace theorizing in medicine, following the example of the physical sciences. â&#x20AC;˘ As the value of these methods in the study of disease became clear, physicians in Great Britain and elsewhere in Europe began to apply them to the effects of traditional drugs used in their own practices. â&#x20AC;˘ Thus, materia medica, the science of drug preparation and the medical use of drugs, began to develop as the precursor to pharmacology. 15

Experimental Pharmacology Area â&#x20AC;˘ However, any understanding of the mechanisms of action of drugs was prevented by the absence of methods for purifying active agents from the crude materials that were available and-even more- by the lack of methods for testing hypotheses about the nature of drug actions.

â&#x20AC;˘ However, in the late 18th and early 19th centuries, Francois Magendie and later his student Claude Bernard began to develop the methods of experimental animal physiology and pharmacology. Advances in chemistry and the further development of physiology in the 18th, 19th and early 20th centuries laid the foundation needed for understanding how drugs work at the organ and tissue levels. 16

Modern Clinical Pharmacology • Paradoxically, real advances in basic pharmacology during the 19th century were accompanied by an outburst of unscientific promotion by manufacturers and marketers of worthless “patient medicines”. • It was not until the concepts of rational therapeutics especially that of the controlled clinical trial, were reintroduced into medicineabout 50 years ago- that it became possible to accurately evaluate therapeutic claims. 17

Pharmacology & genetics â&#x20AC;˘ Some patients respond to certain drugs with greater than usual sensitivity. It is now clear that such increased sensitivity is often due to a very small genetic modification that results in decreased activity of a particular enzyme responsible for eliminating that drug. Pharmacogenomics (or pharmacogenetics) is the study of the genetic variations that cause individual differences in drug response. Future clinicians may screen every patient for a variety of such differences before prescribing a drug. 18

1.3 CHEMICAL PROPERTIES OF DRUGS 1) NATURE OF DRUGS â&#x20AC;&#x201C; Structurally, a drug can be a small molecule or macromolecule: simple element (Li+), salt (CaCO3), complex structure molecule (macrolide antibiotics,insulin). â&#x20AC;&#x201C; Most drugs can be classified acid or base, but in some cases the exact composition of a remedy is not known; it is the case when one uses total extracts from plants. 19

What is called pro-drug ? What is precursor? • Pharmacologically, a drug is designed as pro-drug when the active molecule is fixed on an inactive vector and that will be freed in the organism before acting. Example of pro-drug: – Chloramphenicol-palmitate → chloramphenicol

• A precursor that is an inactive molecule that will be converted to an active form in the body. Example of precursor: – Parathion →paraoxon – L-Dopa →Dopamine 20

2) SOURCES OF DRUGS SOURCES OF DRUGS HERBAL/PLANT Morphine (pavot) Quinine (quinquina) Atropine (belladona) Digoxin (digitalis)

MINERAL FeSO4 NaHCO3 Li2CO3 Al(OH)3

ANIMAL Insulin Globulins Calcitonin

SYNTHETIC Pethidine Amodiaquine Ipratropium Dobutamine

BIOTECH Erythropoietin (EPO)

Examples of Herbal sources Used in Rites and religions

Used as tisane

Encens • Lotus • Gui• Chrysanthemum

Chamomile romaine• Menthe• Tilleul• Thymus vulgaris

Used for essential oil

Used as perfume

Lavande • Thym common •

Encens three • Myrrhe three

Examples of Herbal sources Stupefiant or hallucinogen plants

Toxic plants used as medicines

Cannabis • Coca • Khat • Mandragore • Noix d'arec

Veratre blanc• Petite cigüe • Belladone • Aconit napel •

Molecules extracted from plantes Quinquina (Quinine) • Nux vomica (Strychnine) • Pavot somniferum (Codeine) •

Biotechnology source DNA-Recombinant technology

1.4 PHARMACEUTICAL PROPERTIES 1) Drug nomenclature : three names – Chemical name: • It describes the chemical structure of the active principle

– Generic name: • A short name easily memorable; some time the connotation can evoke an homogenous therapeutic family. • The generic name adopted by WHO is called international common designation (INN). • The generic name is sometimes given by a national commission such as USAN (US adopted name) or BAN (British applied name).

– Trade name or Registered name: • It is given by the manufacturer to a medicine and is protected by a patent. Several trade names can exist for a same drug. 25

Example of Drug nomenclature Chemical name: 7-chloro-2 methylamino-5 phenyl-3H 1,4 benzodiazepine,4-oxide

NH CH3

A N

C Chlordiazepoxyde

Generic name

Libriumď&#x192;˘ Trade name 26

Example of Drug nomenclature CH3 H2N

C O CH2 CH2 N CH3 O Procaine Generic name

Trade names: Novocaine , Allocaine , Servicaine , Chlorocaine, Anestil.

2) Drug dosage forms – Solids: • uncoated, coated tablets, capsules,

– Liquids: • Sterile solutions for Injection • Syrup (suspension, emulsion, solutions) • Eye, ear, nose drops

– Semi solids • • • •

Suppository Ovule Cream Ointment

– Gaseous • Spray • Inhalation

Solid Drug dosage forms Coated or uncoated tablets in various shape & size

Solid Drug dosage forms Tablets

Effervescent tablets

Solid Drug dosage forms Hard gelatin capsules

Soft gelatin capsules

Solid Drug dosage forms Pills & Capsules

Chewable tablets

Suppositories and Ovules

Liquid drug dosage forms Injectable sterile solution

Peroral syrup

Modified-release peroral dosage forms • MR dosage forms are those whose drug release characteristics of time course and/or location are chosen to accomplish therapeutic or convenience objectives not offered by conventional forms. • The acceptable therapeutic concentration of drug at the site of action is attained immediately and is then maintained constant for the desired duration of the treatment. – – – – – –

REPEAT ACTION PROLONGED RELEASE SUSTAINED RELEASE EXTENDED RELEASE [ER] CONTROLLED RELEASE [CR] DELAYED RELEASE

3) Drug Classification – Group of therapeutic agents that are similar because of their • chemical composition or • Pharmacological indication.

– A single drug may be a member of many drug classes. – Example : Aspirin • Chemical class is salicylate • Pharmacological class is analgesic, or antiinflammatory, or antipyretic, or anti-agregant 35

1.5 NEW DRUG DEVELOPMENT PROCESS The process is accomplished in four steps Chemical study

Animal testing

Biological products

Chemical synthesis Compounds

Clinical testing

Marketing

Post market

Trade name

Generics

available

NDA (Patent )

(Patent Expiration)

Phase-I → (is it safe?) in healthy volunteers

Action? Effects? Selectivity? Fate?

Phase-II → (does it work?) → of patients in small group Phase-III (does it work?) in → large group of patients

Phase-IV (is it safe in chronic use? Pharmacovigilance IND

NEW DRUG DEVELOPMENT PROCESS The process is accomplished in four steps 1. Chemical research

2. Animal testing

3. Clinical trial

4. Market approval

Natural source Synthetic source  Active compound

In vivo In vitro  -Action-Effects -Toxicity -Disposition

Phase-I : healthy subjects -Tolerance -Toxicity -Posology -Disposition Phase-II : patients -Efficacy -Tolerance Phase-III : patients -Use

Formulation Approval letter Patent valuable Trade name 

2 years

4 years IND

8 -9 years NDA

Patent expired Generic name

Phase-IV : in market - Pharmacovigilance 17 Years DCI

Animal testing: pharmacology and toxicology profile • Pharmacological action and effects • Acute toxicity • Subacute and chronic toxicity • Teratogenesis • Mutagenesis • Carcinogenesis

Clinical trials Phase-I: 20 to 30 normal volunteers (exception: anticancer therapies are tested in patients with cancer) Phase-II: 100 to 300 patients ( a placebo or positive control drug is included in a single-blind or doubleblind design) Phase-III: 1000 to 5000 patients or more in many centers (a placebo or positive control drug is included in a double-blind crossover design) Phase-IV: post-marketing surveillance phase of evaluation ( toxicities that occur very infrequently will be detected and reported early enough to prevent major therapeutic disasters). Phase-IV is not rigidly regulated as for the three first phases.

Key terms in clinical trials • Placebo: a « dummy » medication made up to resemble the active investigational formulation as much as possible. • Placebo effect: positive therapeutic response due to placebo (psychological response, but not pharmacological). • Single-blind study: a clinical trial in which the investigators, but not the subjects, know which subjects are receiving active medicine and which placebo. • Double-blind study: a clinical trial in which neither the subjects nor the investigators know which subjects are receiving placebo; the code is held by a third party.

Key terms in clinical trials • IND: Investigational New Drug Exemption; FDA approval to carry out new drug trials in humans; requires animal data. • NDA: New Drug Application; FDA approval to market a new drug for ordinary medical use. • Phases I, II, and III: three parts of a clinical trial that must be carried out before submitting an NDA to the FDA. 41

Key terms in clinical trials â&#x20AC;˘ Positive control: a known standard therapy, to be used along with placebo, to fully evaluate the safety and efficacy of a new drug in relation to the others available. â&#x20AC;˘ Orphan drug: drug developed for diseases in which the expected number of US patients is less than 200,000; bestows certain advantages on companies that develop drugs for unusual diseases 42

Chapter-2 PHARMACOKINETICS 2.0 WHAT IS PHARMACOKINETICS DEALING WITH? Study of the Action of the Body on the Drug SITE OF ADMISTRATION D ABSORPTION

BLOOD Qb

ELIMINATION SYSTEMS M E

DISTRIBUTION TISSUES Qt

DRUG ELIMINATION

Study of the processes of Absorption, Distribution, Metabolism and Excretion

2.1. ABSORPTION PROCESS Site of administration Drug release, dissolution, membrane crossing

Re-absorption Enterohepatic cycle

RESORPTION

Elimination First pass effect

I.V.

Liver

YOU WILL LEARN

1. 2. 3. 4. 5. 6. 7.

The routes of administration The release of drugs Dissolution of drugs Membranes crossing through First pass effect Enterohepatic cycle Bioavailability

Blood stream 44

2.1.1 ROUTES OF DRUG ADMINISTRATION Site of administration ENTERAL ROUTES Oral Sublingual** Rectal

Liver

EXCRETION First pass effect

3 LOCAL ROUTES Intranasal Inhalation Transdermal SPECIAL ROUTES Intrathecal Intraventricular

Blood stream PARENTERAL ROUTES Intravascular Intramuscular Subcutaneous

ENTERAL ROUTES ORAL Stomach 窶的ntestine SUBLINGUAL

First pass effect

Liver

RECTAL

Blood stream

Peroral route ADVANTAGES • The most commonly suitable and accepted route

DRAWBACKS • Drugs absorbed from the gastrointestinal tract enter the portal circulation and encounter the liver before they reach the general circulation. • First pass metabolism by the intestine or liver limits the efficacy of many drugs when taken orally. 47

Sublingual route ADVANTAGES â&#x20AC;˘ Placement under the tongue allows the drug to diffuse into the capillary network and therefore to enter the systemic circulation directly. Administration of an agent by this route has the advantage that the drug bypasses the stomach, the intestine and the liver and is not inactivated by the low pH in stomach or by metabolism.

DRAWBACKS â&#x20AC;˘ No valid for chronic administration of great amounts of the drug

Rectal route ADVANTAGES

DRAWBACKS

• Fifty percent of the drainage of the rectal region bypasses the portal circulation; thus the biotransformation of drugs by the liver is minimized. This way also prevents the destruction of the drug by intestinal enzymes or by low pH in the stomach. • The rectal route is also useful if the drug induces vomiting when given orally or if the patient is already vomiting. • The rectal route also is commonly used in young children and also to administer antiemetic agents.

• The rectal bottom part is drained by the lower and middle hemorrhoid veins of which the blood fluxes join the external iliac veins and therefore avoid the passage through the liver and the eventual first pass effect. It is not the case for the fraction of medicine absorbed at the upper site of the rectum. Therefore the absorption by this way is somewhat irregular. • It is not well accepted by some patients.

Parenteral routes ADVANTAGES

DRAWBACKS

• For drugs that are not absorbed orally, there is often no other choice. • The intravenous injection is the most common parenteral route. • The drug avoids the GI tract and, therefore, first-pass metabolism by the liver. • This route permits a rapid effect and a maximal degree of control over the circulating levels of the drug.

•

However, unlike drugs present in the GI tract, those that are injected cannot be recalled by strategies such as emesis or binding to activated charcoal. IV injection of some drugs may introduce bacteria through contamination, induce hemolysis, or cause other adverse reactions by the too rapid delivery of high concentrations of drug to the plasma and tissues. Therefore, the rate of infusion must be carefully controlled. Similar concerns apply to intra-arterially injected drugs. 50

Parenteral routes INTRAMUSCULAR/SUBCUTANEOUS

INTRATHECAL/INTRAVENTRICULAR

• Drugs administered intramuscularly can be solutions or specialized depot preparations – often a suspension of drug in a non-aqueous vehicle, such as ethylene glycol or peanut oil. An example is sustained-release haloperidol decanoate, whose slow diffusion from the muscle produces an extended neuroleptic effect. • Subcutaneous injection minimizes the risks associated with intravascular injection.

• It is sometimes necessary to introduce drugs directly into the cerebrospinal fluid (CSF), such as methotrexate in acute lymphocytic leukemia. • Intraventricular injection can be necessary in emergency cardiac arrest.

Local routes INHALATION

INTRANASAL ROUTE

•

• Intranasal route is used for the administration of some hormones, like desmopressin in the treatment of diabetes insipidus, salmon calcitonin in the treatment of osteoporosis. • The abused drug cocaine is generally taken by sniffing.

• •

Inhalation provides the rapid delivery of a drug across the large surface area of the mucous membranes of the respiratory tract and pulmonary epithelium, producing an effect almost as rapidly as by intravenous injection. This route of administration is used for drugs that are gases, or those that can be dispersed in an aerosol. The route is particularly effective and convenient for patients with respiratory complaints (asthma, COPD) as drug is delivered directly to the site of action and systemic side effects are minimized.

Local routes TOPICAL • Topical application is used when a local effect of the drug is desired. For example, clotrimazole is applied as a cream directly to the skin in the treatment of dermatophytes and atropine is instilled directly into the eye to the pupil and permit measurement of refractive errors.

TRANSDERMAL • This route of administration achieves systemic effects by application of drugs to the skin, usually via transdermal patch. • The rate of absorption can vary markedly depending upon the physical characteristics of the skin at the site of application. • This route is most often used for the sustained delivery systems of drugs such as the antianginal drug, nitroglycerin.

2.1.2 ABSORPTION STEPS 1.Drug release

4. Hepatic first pass

2.Drug dissolution .

.. . .. . . .

Liver

Blood stream 5. Passage into the general circulation

3. Crossing membrane (If any)

1.Factors influencing drug release • PHARMACEUTICAL FACTORS – Drug design form – Excipients



CHEMICAL FACTORS  

Crystalline state Molecular stability

PHYSIOLOGICAL FACTORS  



pH Viscosity Alimentation

Pharmaceutical Factors COATED TABLET UNCOATED TABLET Dissolution of shell

Nucleus

GRANULES

Disintegration Aggregate or Granules Hard CAPSULE

Splitting of flexible shell SOFT CAPSULE

Fusion of shell

Disaggregation POWDER

Wetting and dispersion Suspension Dissolution

SOLUTION 56

Example: Effect of coating â&#x20AC;˘ Enteric coating of a drug protects it from the acidic environment and may prevent gastric irritation. Depending on the formulation, the release of the drug may be prolonged, producing a sustained-release preparation.

Example of Impact of food on drug release Absorption not modified

Extent reduced

Rate lowered

Absorption enhanced

Digoxin :sol Metronidazole : tab Indomethacin : cap Diazepam : tab

Penicillin : cap Ampicillin :cap Tetracycline : cap Erythromycin :tab

Paracetamol :tab Aspirin :efferv. tab Furosemide : tab KCl : tab

Griseofulvin : tab Nitrofurantoin : cap Riboflavin : sol Lithium : tab

Furthermore, the presence of food in the stomach can influence absorption. The presence of food in the stomach delays gastric emptying time so that drugs that are destroyed by acid, for example, penicillin, become unavailable for absorption.

Drug Release in GI Physiology of GI tract Digestive tract :

Segment Mouth

Stomach

Length 0

Duodenum 0.2-0.3 m Jejunum Ileum Colon

Transit duration 0

pH 6.4

Secretion Saliva

1-6 h

1-3.5

HCl, pepsin

1-2 h

6.5

Bile, enzymes

1.5-2.5 m

7.6

2-3 m 12h-4 days

Bacteria flora

2. Mechanisms through which drugs cross cell membrane barriers

4 3

2 1

Mechanisms of Membrane Crossing

Passive Diffusion (liposoluble, unionized molecules)

Facilitated Transport

Filtration (small ions) No saturation process

Active Transport

Saturation process 61

Passive diffusion and Channel filtration 

PASSIVE DIFFUSION Fick’s equation

– q = D.A.(Ce –Ci)/h • D = { Liposolubility, polarity, MW}= diffusion coefficient • A= Membrane surface area • h= Width of the membrane • Ce-Ci= concentration gradient coefficient 

CHANNEL FILTRATION Stokes’ equation

– q= n.r2.A.(Ce –Ci)/h. • n= pores population • r= radius •  =medium viscosity

• The driving force for passive diffusion is the concentration gradient across a membrane separating two body compartments. • No involvement of a carrier, thus, not saturable. • Lipid-soluble drugs readily move through, • Small water-soluble or ionized drugs penetrate the cell membranes through aqueous channels. 62

Active transport and facilitated diffusion • ACTIVE TRANSPORT – Carriers – Against concentration gradient – Energy

• FACILITATED DIFFUSION – Carriers – Concentration gradient dependent

• These processes show saturation kinetics.

• Carrier proteins are specific proteins that span the membrane. • A few drugs that closely resemble the structure of naturally occurring metabolites are transported across cell membranes using these specific proteins. • Active transport is energydependent (ATP) and is capable of moving drugs against a concentration gradient, from a region of low drug concentration to one of higher drug concentration. 63

The effect of pH on the polarity or ionization [ unprotonated form] pH=pKa + log ————————— [protonated form] [ A- ] pH=pKa + log —— [AH]

[ B] pH=pKa + log ——— [BH+ ]

pH= pKa + log(UP/P) UP/P %P %UP pH pKa 10^(pH-pKa) 100*1/(1+UP/P) 100-P 3 3 3 3 6 6 6

3 4 6 8 2 6 9

1 0.1 0.001 0.00001 10000 1 0.001

50.000 90.909 99.900 99.999 0.010 50.000 99.900

50.000 9.091 0.100 0.001 99.990 50.000 0.100

The effect of pH on gastrointestinal absorption

The drug has been assigned a pKa of 6.5

The effect of pH-partition on the passive diffusion in GI tract • A drug passes through membranes more readily if it is uncharged. • For a weak base, the uncharged form, B, is predominant in intestine. For a weak acid, the uncharged form, HA, predominates in stomach. However, weak acids are also absorbed in intestine because it offers large surface area for absorption compared to stomach. • For strong acids or bases, the charged form in predominant both in stomach and intestine. Therefore, they are not absorbed at any site, or are less absorbed. • For very weak acids or bases, the uncharged form predominates both in stomach and intestine; therefore, they are absorbed at any site.

The Hepatic First Pass Effect • Oral (totally ); Rectal (partially) • Sublingual (negligible) • Small molecule, Lipid soluble, unionized • Prolongation of action; Prolongation of toxicity • During the first pass the liver can extract some amount that is excreted in the bile and this does not reach the general circulation. The clearance may be very important for some drugs restraining them from being given per oral route. 67

WHAT IS BIOAVAILABILITY? • MEASUREMENT OF THE RATE AND THE EXTENT OF ABSORPTION • F= Q/D • Factor of bioavailability= The fraction of the dose administrated that actually reaches the blood stream; that is available to site of action.

DOSE=D

STOMACH

INTESTINE

Loss-1

Loss-2

LIVER

Loss-3

QUANTITY AVAILABLE=Q

BLOOD

Q=D-L1-L2-L3 68

QUANTITATIVELY YOU WILL LEARN ABOUT THE BIOAVAILABILITY 1. The rate: How fast the drug enters the systemic circulation? 2. The extent: What fraction of the administered drug amount actually reaches the systemic circulation? 3. Bioequivalence: When two medicines have comparable bioavailability?

mg/L

30 Peak concentration

20 10 0

AUC

1 2 4 Peak time RATE

Area under the curve h.mg/L

Time

Area Under the Curve EXTENT

MEASUREMENT OF BIOAVAILABILITY mg/L

mg/L Peak concentration

h.mg/L

20 10

AUC

0 0

Peak time ABSORPTION RATE

Time

hrs Area Under the Curve ABSORPTION EXTENT

Take blood samples at different times after administration. Measure the concentration using an appropriate tool and method. Plot on X-Y scale. 70

MEASUREMENT OF BIOAVAILABILITY AUCoral x DOSEiv F=

mg/L 30

AUCiv

x DOSEoral

20 AUC iv

ORAL

SSC

10 hrs

Carry out experiment by IV administration; Repeat the experiment by oral administration; Compare the AUCs. F=1 means the total dose is absorbed; F=0 means nothing is absorbed ; 0<F<1 means partially absorbed.

AUC peroral SSC

2.2. DISTRIBUTION PROCESS • YOU WILL LEARN ABOUT – Importance of binding of drugs to plasma proteins – Importance of tissue blood flow and tropism – Importance of natural barriers – Volume of distribution as parameter for quantification

2.2.1 What is drug distribution? â&#x20AC;˘ Drug distribution is the process by which a drug reversibly moves between the blood stream and the tissue space. â&#x20AC;˘ The drug may be located in three compartments: intravascular, interstitial, and intracellular.

2.2.2 STEPS INVOLVED IN DRUG DISTRIBUTION • DILUTION IN THE PLASMA – When a medicine enters the blood circulation, it is first diluted in plasma;

• PROTEIN BINDING – A fraction can bind to the plasma proteins.

• DIFFUSION INTO THE TISSUES – The free fraction diffuses in the interstitial space toward different tissues, including the site where it will act. However, other tissues such as the brain appear to be protected against a massive entry of most chemical molecules.

• BINDING TO TISSUE COMPONENTS – In a given sector, the drug can bind to molecular sites named receptors where the liaison triggers an action, or acceptors sites if the liaison is inactive.

• ACCUMULATION INTO THE TISSUE – A tissue can present a tropism or a particular affinity with some drugs.

DETERMINANT FACTORS FOR DISTRIBUTION â&#x20AC;˘ The delivery of a drug from the plasma to the tissue primarily depends on: 1. the degree of binding of the drug to plasma proteins 2. the blood flow through the tissue 3. the capillary permeability 4. the relative hydrophobicity of the drug 5. the degree of binding of the drug to tissue components (tropism) 75

Importance of protein-binding • Drug molecules may bind to plasma proteins (usually albumin). • Only the free, unbound drug can leave the blood stream and enters the interstitium. • Thus, by binding to plasma proteins, drugs become « trapped » and, in effect, inactive. • [Note: hypoalbuminemia may alter the level of free drug] 76

Types of binding to plasma proteins Albumin • The albumin is the most abundant protein, it represents 50 to 60%. It is a single polypeptide chain with the mass approximating 69.000 and composed of 610 amino acids (alternation of 20 amino acids). The albumin offers a small number of binding sites to acidic drugs (basic groups : arginine, histidine, lysine), but the liaison bond is strong. The phenomena of saturation and competition between drugs are possible because of this small number of available sites. Globulins • Globulins are polypeptides of variable molar mass according to the class to which they belong (, ,  ). They play a big role in immunity and the regulation of the biologic activities. 1-Glycoprotein acid • It is the smallest of the plasma proteins ; its mass varies around 41.000. It is a very soluble and very steady protein, because 41% of the molecule are constituted of carbohydrates. The bases have a bigger affinity for the other proteins that for the albumin, in particular α1-glycoprotein acid. The number of binding sites (acidic groups) on the albumin is high, and therefore the phenomena of competition and saturation are rare.

Comparative binding strength High capacity Salicylic acid Dicoumarol Digitoxin Erythromycin Furosemide Indomethacin Phenylbutazone

% 98 99 91 93 99 97 99

Mid capacity Aspirin Chloramphenicol Penicillin G Phenobarbital Quinidine Streptomycin

% 61 70 52 50 75 35

Weak capacity Oxytetracycline Ampicillin Digoxin Gentamicin Paracetamol Isoniazid

% 31 13 29 10 4 0

Kinetics of drug binding to proteins • M = drug concentration • Ptotal = P +  MP • K= dissociation constant at equilibrium • r = fraction bound (%) • n = number of binding sites

Kinetics of binding of drug to proteins 1°) Double reciprocal transformation

2°) Woulf transformation

1/r = 1/n + (1/nK).(1/M )

M/r = 1/nK + 1/n.M

Importance of blood flow Organ Lungs Kidneys Liver Heart Brain Muscle Skin Fat

Flow (ml/min) 5000 1100 1350 200 700 750 300 200

Perfusion (ml/min/100 g) 1000 400 80 60 50 2.5 2.4 3 81

Importance of blood flow • The distribution essentially reflects the regional blood fluxes. • An initial phase of distribution will concern only organs richly vascular : heart, liver, kidneys, brain. • These organs receive the major part of the drug during the first minutes that follow the intravascular administration. 82

Importance of blood flow â&#x20AC;˘ A second phase of distribution can be distinguished; it also is limited by the blood flux and interests the large part of the total body mass : muscles, viscera, skin, and the fat. â&#x20AC;˘ For these tissues, the equilibration with blood can take several minutes or hours to complete.

Drug lipophilicity and tissue-tropism • The distribution to the intracellular compartment depends on the drug’s solubility in the lipids (except if the drug uses a physiological carrier). • The distribution in a given tissue not only depends on the blood flux and the speed with which the drug distributes in tissue, but also on the capacity of binding to the tissue’s constituents (selective affinity or tropism). 84

Drug targeting â&#x20AC;˘ It can be interesting to tempt to modify the normal distribution of a medicine in order to encourage its interaction with target tissue (drug targeting) and to avoid undesirable effects to the level of other tissues. â&#x20AC;˘ This objective is especially sought-after in anticancer therapy. One has very active drugs against the cancerous cells, but that can be very toxic for some normal tissues, notably the tissues that divide quickly. â&#x20AC;˘ The doxorubicin is a very toxic antitumor agent for the heart. One proposed to couple this drug to controlled monoclonal antibodies against some specific antigens present to the surface of the cancerous cells. One achieves a pro-drug thus without affinity for the normal cells, and that concentrates in the cancerous cells. Inside of these, the complex is damaged and free the active drug.

Blood-brain barrier • The passage of drugs out of the capillaries toward the cerebral interstitial liquid is limited by the Blood Brain Barrier (HEB); • The passage from the plexuses toward the CRL is limited by the hematoliquid barrier(HLB), and • The passage from the CRL toward the encephalon by the liquid-encephalon barrier (LEB).

Blood-Brain Barrier â&#x20AC;˘ The brain is the most richly vascular organ. The blood flux is estimated there to 0.5 ml/g and per minute, whereas it is of 0.05 ml in the muscles at rest. â&#x20AC;˘ However, the accumulation of numerous chemical substances in the encephalon and in the cephalorachidian liquid is from afar lesser that in the other sectors of the organism. â&#x20AC;˘ The access to the nervous centers occurs, either by the cerebral capillaries, either while passing by the cephalorachidian liquid. 87

Blood-Brain Barrier • The cerebral capillaries are particular because their present endothelium doesn't has intercellular pores. • Besides, the capillaries are surrounded with glial cells (the astrocytes) so that the drug that must cross has double cellular layer before reaching the cerebral interstitial liquid. The glial cells reduce the interstitial space that is only of 1-2% instead of 20% in the other sectors. • From then one, the passage through the hematoencephalic layer is only possible for the very lipid-soluble substances like the pentothal. • Phenomena of active transportation that permit the passage toward the brain of essential substances such as the amino acids, exist however. Some substances, like dihydroxyphenylalanine (LDopa) that is used as antiparkinsonian drug, are actively transported. 88

Placental Barrier: drugs in pregnancy

Distribution of drugs in pregnancy • The placenta plays at the fetus, the devolved roles in the adult: – to the alveolar partition (breathing) – to the digestive mucous membrane (nutrition) – to the kidneys (elimination).

• The placenta also plays the protective role, and is capable to metabolize numerous substances.

Distribution of drugs to fetus • Blood is distributed in the fetus according to the particular needs of every organ : nonfunctional or little functional organs such as the lungs, are excluded practically. • The cardiac debit is of 0.25 l/kg per body weight, the frequency of 130 to 160/min. • About 50% of blood coming from the fetal heart go toward the placenta, the rest nourishes the body (35%) and the lungs (15%) of the fetus. The left heart and the right heart are plugged in parallel; an installation in series as in an adult is not necessary at this stage. 91

Equibrium between the mother and fetus â&#x20AC;˘ The balance between maternal blood and fetal tissues is only reached after at least 40 minutes (it explains that at the course of a caesarean, the extraction of an awake child is possible if it intervenes 10 to 15 minutes after the mother's anesthesia). â&#x20AC;˘ Some fetal tissues are sensibly vulnerable to the action of the drugs. â&#x20AC;˘ The fetal liver receives an important quantity of drug because of its irrigation, but the enzymatic immaturity doesn't allow him to assure, far from there, the totality of the biotransformations normally assured by the maternal organism and the placenta. 92

2.2.3 THE VOLUME OF DISTRIBUTION • Total body water is about 42 liters / 70 kg

2,8-4,2 L

•

6,2- 9,8 L 21 – 28 L

The obvious volume of distribution (Vd) of a drug is the virtual volume in which the totality of this drug would be distributed uniformly to give the concentration measured in plasma. The obvious volume of distribution is a mathematical ratio and corresponds only rarely to a physiological volume. The nortriptyline, for example, has a volume of about 1100 liters for a person of 70 kg, what overpasses the extensively total liquid volume of the organism (42 liters).

CALCUL OF THE VOLUME OF DISTRIBUTION • The volume of distribution measures the importance of diffusion of the drug in the tissue compartment: the larger is Vd, the extent is the amount that enters the tissues, and vice versa. – – – –

F= Bioavailability factor Dose= administered dose Cp= drug concentration in plasma F.Dose = Q= quantité présente dans le corps

After IV administration

After peroral administration

2.3 ELIMINATION PROCESS • YOU WILL LEARN ABOUT – RENAL ELIMINATION – HEPATIC ELIMINATION – OTHER ROUTES OF DRUG ELIMINATION – DRUG BIOTRANSFORMATION – CLEARANCE

2.3.1 WHAT IS ELIMINATION? • The elimination encompasses the processes of biotransformation and excretion that terminate the action of drug by removing it from the site of action. • Excretion is the process whereby materials are removed from the body to the external environment. • Biotransformation, or metabolism as it is frequently called, is the process by which chemical reactions carried out by the body convert a drug into a compound different from that originally administered.

2.3.2 ROUTES OF ELIMINATION

BLOOD

BILE & FECES EXPECTORATION

URINE

OTHERS

ROUTES OF ELIMINATION • The two major organs of elimination of drugs are the kidney and the liver. • The most important vehicle by far the excretion of nonvolatile, watersoluble drugs is the urine. There are many instances in which a drug or the product of its biotransformation or both are excreted almost entirely by this route. • The liver, through its secretion of bile into the small intestine, contributes the major portion of material excreted in this manner. • The lung is the major organ of excretion for gaseous substances. • Sweat , tears, saliva, nasal excretion and the milk of the lactating mother are all examples of other fluids in which drugs may be excreted. The amount excreted by any of these routes ordinarily represents only a minor fraction of the total amount of drug eliminated from the body.

2.3.3 Renal excretion Tubular Reabsorption Glomerular Filtration

Tubular Secretion

E= F + S - R

Urine Excretion

Quantitatve aspects of urine formation per 24 hours Substance

Filtered

Secreted

reabsorbed

Excreted

Percent reabsorbed

Sodium ion (mEq)

26,000

25,850

150

99.4

Chloride ion (mEq)

18,000

17,850

150

99,2

Bicarbonate ion (mEq)

4,900

100

Urea (mM)

870

460

410

Glucose (mM)

800

100

Water (ml)

180,000

179,000

1,000

99,4

Hydrogen ion Potassium (mEq)

Variable 900

100

Variable 900

100

Glomerular filtration • The rate of filtration through the glomeruli (GFR) is estimated to 125 ml/min. • The fraction of the drug filtered (mg/min) = GFR(ml/min) x free Concentration (mg/ml) • The quantity of the drug entering the tubular lumen depends on the rate of glomerular filtration and the capacity of the drug to bind to the plasmatic proteins. • Blood passing in the capillaries of the glomerular leash to filter, through the pores of the capillaries and the visceral leaflet of the capsule of Bowman, both ionized and non ionized molecules with the exception of those bound to the plasmatic proteins. The filtration provides a ultrafiltrate of plasma deprived of proteins. 101

Tubular secretion • Some organic cations and anions are actively secreted in the tubular lumen by cells of the proximal tubule. • Several organic acids (penicillin, indomethacin, phenylbutazone…) and some metabolites are transported into the tubular lumen by a certain specific systems that carry the uric acid notably. • Of the organic bases (quaternary ammonia, quinine, dihydromorphine…) are transported by the way that endogenous organic bases (choline, histamine) follow. 102

Tubular reabsorption • In the proximal and distal tubules, the lipid-soluble materials, including the non ionized of weak acids and bases, are passively reabsorbed. The gradient of concentration is created by the reabsorption of water that comes with the one of Na+ and other inorganic ions. • The difference of pH between plasma and the content of the tubules influence the reabsorption of acids and weak bases following the theory of ‘pH ' partition. • The content of the distal tubule is slightly acidic, that governs the reabsorption of the weak acids and the excretion of the weak bases. 103

Tubular reabsorption • In the treatment of some poisonings, one can accelerate the excretion of a toxic compound by playing on the urinary pH, that can vary from 5 to 8. One can, thus, treat a poisoning by an acid such as phenobarbital, in alkalinizing the urinates by means of an intravenous drip of sodium bicarbonate. • Inversely, alkalinizing the urinates will decrease the excretion of a weak base (e.g. amphetamine). • • • •

Urinates Acidifiers -vitamin C -ammonium chloride -arginine.HCl

Alcalinizers -bicarbonate de sodium -carbonate de calcium -carbonic anhydrase inhibitors 104

2.3.4 Hepatic elimination • The hepatic capillaries have the pores whose width can permit the passage of the proteins in blood. • In addition to its main role that is the metabolism, the liver excretes many compounds and their metabolites in the bile. • The secretion of the bile is controlled mainly by the humeral way (secretin, cholecystokinin), and incidentally by the nervous way. The food rich in proteins increases the secretion, and the food rich in lipids decreases it. • Normally, it forms per day about 0,5 to 1 l of bile composed of water and the biliary acids. In the duodenum, more than 90% of water and biliary salts are reabsorbed (enterohepatic cycle). 105

Biotransformation of drugs • Biotransformation is the process by which chemical reactions carried out by the body convert a drug into a compound different from that originally administered.

• The liver is the main organ where intervenes the biotransformation of xenobiotics. • However, the catabolism of numerous medicinal substances can occur at other places, namely: – – – – – –

the digestive tract, blood, the lungs, the gonads, the placenta, the site of action (synapse sift), etc. 106

Types of Reactions of Biotransformation Phase-1 Reactions Fictionalization

Phase-2 Reactions Synthesis

1° Ester function

1° Glucuronoconjugaison (glucuronidation) • glucuronyltransferase 2° Sulfoconjugaison (sulfation) • APS kinase 3° Conjugaison with Glycine • H2N-CH2-COOH +R-CO-S~CoA  R-CONH-CH2-COOH 4° Acetylation • R-NH2 + CoA-S-CO-CH3  R-NHCO-CH3 + CoA-SH 5° Methylation • R-XH+ S-adenosylmethionine  • R-X-CH3 + S-adenosylhomocysteine

R-CO-O-R’

+ H2O ↔ R-COOH + R’-OH

2° Amide function R-CO-NH-R’ + H2O ↔ R-COOH + R’-NH2

3° Aldehyde function • R-CHO ↔ R-CH2OH 4° Diazo • R-N=N-R’ ↔ R-NH2 + R’-NH2 5° Unsaturated bond • R-CH=CH-R’ ↔ R-CH2-CH2 6° Nitrite group • R-NO2  R-NO ↔ R-NOH  R-NH2 7° Carboxyl group • R-CH(COOH)-R’ ↔ R-CH2-R’ + CO2

107

Consequences of the biotransformation • The major aim of the biotransformation of the foreign substances (xenobiotics) in organism is the formation of the derivatives that are polar, inactive and non toxic, and which can be excreted easily in the bile or the urine. • The biotransformation is therefore an essential stage permitting the elimination of the lipid-soluble compounds. • However, the metabolism can have other consequences: – conversion of an inactive substance or atoxic in active or toxic derivative – formation of a more lipid-soluble metabolite than the drug

108

Enzyme Complex implied in the metabolism of drugs • The homogenate of the hepatic cells gives, after centrifugation, two fractions of which one is water-soluble and the other insoluble. • The soluble fraction contains various enzymes implied in the control of the cellular activity (GOT, GPT, LDH….) and the specific enzymes for the metabolism of the endogenous substances (alcohol dehydrogenase, xanthin oxydase, tyrosine hydroxylase, etc.) • In the fraction insoluble so-called " microsomial“, there are enzymes called ‘multi-functional ' (oxydoreductases, hydroxylases) operating via special proteins named P450 cytochromes. • The non specific enzymes are particular in that they are incapable to activate the metabolism of the specific highly stereo endogenous substances.

109

Enzyme Complex implied in the metabolism of drugs • The smooth reticulum endoplasmic of the liver contains an important group of enzymes called monooxygenases or P450 cytochromes. • The P450 cytochrome is associated to another enzyme (containing a likely FAD cofactor), the cytochrome P450 reductase. • One knows currently in human species at least twelve families of genes coding for cytochromes slightly different (P450 isoforms). • However, some reactions essentially depend well on a particular isoform: if it is genetically abnormal or absent, the life span of the drug will be prolonged and some toxic phenomena can occur. 110

Examples of Biotransformation of drugs Formation of Inactive Metabolites Active Drug Inactive Metabolite Pethidine → Demethylpethidine Noradrenaline → Normetanephrine Sulfanilamide → Acetylsulfanilamide Chloramphenicol → Chloramphenicol glucuronide Formation Active Metabolites Active Drug Codein → Aspirin → Diazepam → Digitoxin → Inactive Drug Prontosil → Parathion →

Active Metabolite Morphine Salicylic acid Demethyldiazepam Digoxin Active Metabolite Sulfanilamide Paraoxon 111

Metabolism of Paracetamol â&#x20AC;˘ The primary metabolic pathway for paracetamol is glucuronidation. This yields a relatively non-toxic metabolite, which is excreted into bile and passed out of the body. A small amount of the drug is metabolized via the cytochrome P-450 pathway (to be specific, CYP1A2 and CYP2E1) into NAPQI, which is extremely toxic to liver tissue, as well as being a strong biochemical oxidizer.

112

Factors influencing biotransformation Age â&#x20AC;˘ The hepatic systems of biotransformation are not fully developed in the newborn, especially the premature (e.g. glucuronoconjugaison lack). â&#x20AC;˘ The natural compounds (bilirubin) and the drugs (e.g. chloramphenicol) that are deactivated mainly in this manner appear more toxic during the postnatal period. â&#x20AC;˘ In the oldest subjects, the hepatic mass cuts down and the enzymatic activities as well, in particular the P450 cytochromes, decrease. Thus, some drugs (e.g. benzodiazepine often taken chronically) will be metabolized more slowly. 113

Factors influencing biotransformation • Genetic heritage – The capacity of biotransformation can vary according to the genome, and it can entail some variations in the therapeutic and toxic effects of the drugs. – When several genes intervene in the biotransformation of a drug, the variability between individuals results in a unimodal distribution of the answer to the drug. – If only one gene is major, one observes bimodal or trimodal distribution types. One speaks of genetic polymorphism. 114

Polymorphism in drug metabolization • Polymorphism of acetylating : – inactivation of the isoniazid, one observes a bimodal distribution with regard to the speed of acetylation, distinguishing between fast acetylors and slow acetylors, that are in relatively equal proportion in various populations. – The slow acetylor is more sensitive to the toxic action of the isoniazid itself (polyneuritis), while the fast acetylor experiences liver toxicity due to a metabolite acetylisoniazid that is converted in a toxic metabolite for the liver.

• Polymorphism of oxidation : – In 5-10% of the individuals in human populations, an isoform of P450 is absent and that slows the oxidation of several drugs.

• Polymorphism of hydrolyze – The succinylcholine (suxamethonium) is normally quickly hydrolyzed by a plasmatic esterase (pseudocholinesterase). The length of action of this curare is generally brief, 1-2 minutes, but in some people (1/2500) it can be of 1 hour and more. This abnormality is due to the presence of an abnormal esterase, controlled by a recessive gene.

115

Factors influencing biotransformation â&#x20AC;˘ Pathological State â&#x20AC;&#x201C; The biotransformation of the medicines can be affected by several illnesses, in particular, in case of hepatic attack or cardiac insufficiency

116

Factors influencing biotransformation • Induction of the microsomal enzymes activity

– A certain number of drugs and substances present in the environment are capable of inducing the synthesis of hepatic enzymes (monooxygenases and glucuronyltransferases). Their common character is of being lipid-soluble at the physiological pH. – One distinguishes two groups of inducers, classically: • the group of the phenobarbital especially acting in the liver and the intestine and in a relatively slow manner (the induction only developing itself after several days) ; • the groups of polycyclic aromatic hydrocarbons (smoke of cigarette, meats cooked to the barbecue), that exercise their inductive effects on most tissues and have a faster action (hours). 117

Consequences of drug metabolism induction • The enzymatic induction has for consequence the acceleration of the biotransformation of the inductive and/or other substances on which can act the led enzymes. • A progressive reduction of the effect of the substances of which biotransformation is accelerated results from it. • If it is about the auto-induction, one observes the installation of a phenomenon of tolerance : to recover the same effect, it is necessary to increase the managed dose. 118

Examples of inducers of hepatic enzymes Auto-inducers of hepatic microsomal enzymes ď&#x20AC; Phenobarbital (barbiturates) Hetero-inducers -Griseofulvin -Phenylbutazone -Phenytoin -Rifampin

119

Examples of inhibitors of enzymes Inhibitors of hepatic microsomic enzymes  Cimetidine  Iproniazid  Ketoconazole  Imipramine Inhibitors of specific enzymes  monoamine oxydase inhibitors (IMAO)  Inhibitors of acetylcholinesterase Non specific competitive inhibitors  Aspirin inhibits the metabolism of chlorpromazine  Chloramphenicol inhibits the metabolism of hexobarbital  Disulfiram inhibits the metabolism of alcohol 120

2.3.4 What is clearance? • The Clearance – The clearance represents the volume of liquid of which a substance is completely purified by unit of time (ml/min). – It represents the ratio of the rate of elimination on the concentration of the substance in plasma: (∆Q/∆t)/Cp.

• Constant of elimination – The constant of elimination expresses the fraction of the drug eliminated by unit of time.

• Half-life of elimination – The biologic half-life indicates the time required to excrete half of the total absorbed amount of the drug. – The plasmatic half-life indicates the time required to halve the plasmatic concentration measured at a given time.

121

Calculation of Half-life Cp

Ln Cp

Ke Ka

T1/2

122

Body clearance • The total clearance of the organism is the sum of the clearances of every organ of elimination. • Thus, for a drug eliminated completely by the liver and the kidneys, the body clearance will be of about 3000 ml/min, that corresponds to the sum of the renal and hepatic blood flows (or the half of the cardiac output). • However, the clearance of most drugs is distinctly lower than this value. 123

Calculation of renal clearance

Clr =

Concentration urine x Volume urine/24h  Concentration plasma

Cu x Vu Clr (ml/min)= Cp x 1440 • The creatinine and the inulin are neither secreted, nor reabsorbed in the tubules ; their clearances represent the rate of glomerular filtration that is about 125 ml/min. The reduction of this value is a sign of a possible renal insufficiency. 124

Factors modifying clearance of drugs • Age : – The maturation of the renal function is progressive at the childhood, becoming complete from year -1 old . At the older age the renal capacity of excretion decreases.

• Sex : – The woman's clearance is slightly lesser than in man (80 to 85%).

• Pathologic state : – Cardiac insufficiency – Renal insufficiency

• Drug Interactions – The competition for the tubular secretion (Penicillin and probenecid) or the modification of the urinary pH can delay or can accelerate the speed of elimination.

125

Variation of the renal clearance with age Age

Inulin Clearance (ml/min/1,73 m2 )

1 to 10 days 1 month 6 months 12 months 1 - 70 years 70 – 80 years 80 – 90 years

15 – 45 30 – 60 50 – 100 80 – 120 120 70 – 100 45 – 85

normal value

126

Liver functioning test • The bromosulfophtalein (BSP) is used to measure the hepatic purification capacity. • One determines the concentration measured in plasma at 3 minutes and at 45 minutes after administration of 5 mg of BSP by intravenous way; then one calculates the ratio (R): Concentration at 45 min R=  Concentration at 3 min R R R R

0 - 5% = normal function 5 – 25% = minor damage 25 – 75 % = moderate hepatic damage  75 % = severe hepatic damage

127

Functional biomarkers Normal range creatinine male female child Uric acid male female child bilirubine total direct conjugated urea

7 - 13 mg/l 5 - 10 mg/l 1,75 à-4,4 mg/l

60 -115 µmol/l 45 -90 µmol/l 15 -40 µmol/l

35 - 70 mg/l 25 - 60 mg/l 20 - 40 mg/l

210 -420 µmol/l 150 -360 µmol/l 120 -240 µmol/l

3 - 10 mg/l 3 mg/ml 0.10 -0.60 g/l

5 - 17 µmol/l 5 µmol/l 1.66 - 10 mmol/l 128

Functional biomarkers ALAT = SGPT ASAT = SGOT LDH CPK Gamma GT Phosphatase alkalines Amylase

< 40 U/l < 40 U/l < 195 U/l < 60 U/l 21 -58 U/l 1 -34 U/100ml 60 -100 U/l

129

Chapter-3 PHARMACODYNAMICS • YOU WILL LEARN ABOUT • • • • • •

DEFINITION OF DRUG ACTION AND DRUG EFFECT RECEPTORS CHEMICAL MEDIATORS (PRIMARY MESSENGERS) SECONDARY MESSENGERS AGONISTS AND ANTAGONISTS AFFINITY , EFFICACY , POTENCY OF A DRUG

130

3.1 DEFINITIONS • WHAT IS PHARMACODYAMICS? – The pharmacodynamics deals with the action of the drug on the organism while pharmacokinetics deals with the action of the organism on the drug. – The pharmacodynamics describes the nature and the intensity of the biologic effects produced by various drugs in the living organisms. – The pharmacodynamics illuminates the mechanisms of action or molecular interactions upon which biological effects root. 131

DEFINITIONS • Biophase = is the site of action • Action = biochemical events occurring at the biophase (microscopic event): Ca++ increase • Effect = physiological event triggered by the action (macroscopic event): Contraction

• Action and Effect may occur at the same place or at different places • For examples: • Atropine produces its mydriase effect (pupil opening) by acting on the eye; while • Morphine produces its myosis effect (pupil closing) by acting centrally on CNS.

132

MECHANISMS OF ACTION • Most of drugs bind to special protein sites called receptors to initiate their action. • Only small number of drugs don’t bind to receptors and act through chemical or physical or mechanical interactions like – Neutralization of gastric acidity by antacid drugs is chemical reaction. – Adsorption of toxins in gastrointestinal tract by medical charcoal is a physical way. – Some purgative drugs act mechanical by irritating intestine.

MECHANISMS NOT EVOLVING RECEPTORS

MECHANISMS EVOLVING RECEPTORS

DIRECT ACTING PHYSICAL INTERACTION

INDIRECT ACTING

CHEMICAL INTERACTION

133

3.2 THE CONCEPT OF RECEPTOR Recognition Second Messenger Inactive

Binding Activation

Removal Inactivation

Second Messenger Inactive ACTION Second Messenger Activated

EFFECT

Second Messenger Inactive

END of EFFECT 134

THE CONCEPT OF RECEPTOR • The concept of receptor was first suspected by Ehrlich and Langley in the end of 19th century. • Working with curare, a hunting poisonous used by south American Indians, Langley observed that this substance blocks the contraction of muscle induced by nicotine, but was no effect on contraction induced electrically. Langley hypothesized that nicotine and curare interacted by binding to a common molecular structure in the body. • Later in early 20th century, Ehrlich wrote « corpora non acunt nisi fixata ».

135

3.2.1TYPES AND LOCATION OF RECEPTORS SUPER FAMILIES OF RECEPTORS Ligand gated channel receptor Protein kinase enzyme

E DNA

G-protein Enzyme

CELL LOCATION OF RECEPTORS

• There are three types of receptors located on the cell membrane: – Channel type receptors – Enzyme type receptors – Protein-G type receptors;

• and one type located into the cytoplasm. – Cytosol-DNA type receptors

G-protein Channel 136

Transmembrane signaling receptors â&#x20AC;˘ Most transmembrane signaling is accomplished by a small number of different molecular mechanisms. â&#x20AC;˘ Each type of mechanism has been adapted, through the evolution of distinctive protein families, to transduce many different signals. â&#x20AC;˘ These protein families include receptors on the cell surface and within the cell, as well as enzymes and other components that generate, amplify, coordinate, and terminate post-receptor signaling by chemical second messengers in the cytoplasm.

137

3.2.2 STRUCTURE OF MEMBRANE RECEPTORS R-C R

Na+

R-E Enzyme

Channel

Substrate inactive R-G-C R

G-Channel

Active Product

G-Enzyme

R-G-E

Substrate inactive

Active Product 138

CHANNEL RECEPTORS 



We distinguish two groups of channel receptors: activating channels 

Na+ and Ca ++ channels

 inhibiting channels – Cl- and K+ channels

A channel is constituted of several polypeptide sub-units harshly associated to each other. It’s a pentameric protein containing four subunits of 5 kDa () , 53.7 kDa (), 56.3 kDa () et 57.5 kDa () respectively, associated in stoechiometry 2. An electronic microscope view shows a transmembrane protein of 11 nm length (rosulate layer) and 7 nm diameter whose central sift forms the channel. 139

CHANNEL RECEPTORS • Voltage-gated channels (e.g. Na+ and K+ channels found at nerve axons and terminals). • Extracellular ligand-gated channels (e.g. nicotine acetylcholine receptor, GABA receptor and glycine receptor channels that are mostly regulatory neurotransmitters). • Intracellular ligand-gated ion channels (e.g CFTR or Cystic Fibrosis Transmembrane conductance Regulator belonging to ATP-Binding Cassette family known as ABC family; sense perception channels which are activated indirectly by GCPRs; calcium ions; cAMP and cGMP; as well as phosphadidyl inositol). • Mechanosensory and volume-regulated channels. • Miscellaneous channels (e.g. Gap junctions and peptide ion channels like gramicidin). 140

KINASE ENZYME RECEPTORS KINASE ENZYME RECEPTOR

G-PROTEIN RECEPTOR

Seven membrane G-protein receptor 141

G-PROTEIN RECEPTORS D

Inactive

GDP

GTP active

Depolarization Ca++ release

Second messenger Phosphorylation

Cellular Effect

Other

3.3 Second messengers coupled to G-Protein Sub-family G

Effector

Cell Message

Adenylylcyclase

- cAMP increase

-Adenylylcyclase -Phospholipase C -Phospholipase A2 -Phosphodiesterase -Channel- Ca++ -Channel- K+ Phospholipase C

Go (transducine)

Phosphodiesterase cGMP dependant (rhodopsin)

- cAMP reduced -IP3 and DAG reduced -arachidonic acid formation - cGMP reduced -fall in intracellular Ca++ -hyper polarization -IP3 and Ca++ increase -DAG and protein-kinase activation -mechanism of light photon absorption by retina

There are at least 20 different sub-unit ď Ą , but only four protein-G sub-families are important : Gs, Gi, Gq and Go. 143

SECOND MESSENGERS (cAMP and cGMP)

NH2

NH2 N

O -O

O H H

H H OH

N -O

O-

H OH

144

Phospholipase-C IP3/DAG /Ca++ pathway Phosphatydyl-inositols (PdIns) + ATP

PdIns-4,5-diphosphate (PdIns-4,5 Pi) Phospholipase-C Phosphatidic acid (PA) Inositol- 1,4,5-triphosphate (IP3)

Diacyclglycerol (DAG)

Inositol

DAG remains bound to membrane, but IP3 enter the cytoplasm where it triggers 145 calcium mobilization out of endoplasmic reticulum

Role of Ca++ as Second Messenger • At rest, the intracellular concentration of calcium is around10-7 M. At that level not all the proteins may interact with calcium , but very small. • During cell activation, Ca++ concentration may remain steady or regularly waive in peak-valley. • When the concentration reaches 10-6 to 10-5 M many calciproteins bind calcium and are activated. • The effect worked out (i.e. contraction, secretion) depends on the type of the target cell. 146

Calciproteins and their actions Calmodulin and analogs

Annexin and analogs

Calmodulin

Annexin-I Inhibition of PLA2 (lipocortin- I ) Annexin- II Exocytose process Annexin- V Blockage of factor VII to bind factor X ( no coagulation)

Troponin C Recoverin

Enzymes activation

Interaction myosin-actin Retinal guanylylcyclase activation to restore the polarity of discal membrane Paravalbumin, Buffers to cytosolic Ca++ calretinin and calbindine

Annexin-VII

Forms ion channels

147

Example of NO activation M R Ca++ + Calmodulin

Ca-Calmodulin

NO synthetase inactive

NO synthetase activated NO + Citruline Guanylylcyclase inactive

Guanylylcyclase activated

cGMP

GTP

Arginine

Effect

VASODILATION or MUSCULE RELAX

PDE GMP (inactive) NO (nitric oxide); GTP (guanosyl triphosphate) ; cGMP (cyclic guanyl monophosphate GMP (guanyl monophosphate ); PDE (phosphodiesterase )

148

Activation of cytosolic receptors Hydrocortisone D

Active Protein Lipocortin hsp90

Phospholipids PLA2 Arachidonic acid

D D Prostaglandins

Leukotrienes

Inflammation

Asthma 149

Activation of cytosolic receptors • Cytosolic receptors are mobile proteins , located inside the cytoplasm, and have a specific binding side for DNA genes, which is hidden by a special protein called « heat-shock protein » (hsp90). • Once an agonist binds to receptor, hsp90 is temporally removed and the complex Agonist-Receptor moves to nucleus where it binds to a specific gene and activates it. • The activated gene expresses itself by synthesizing a correspondent mRNA that will commends the synthesis of active protein, through ribosomal process, back in the cytoplasm. 150

Phospholipase A2-Arachidonic Acid pathway

151

3.4 MEDIATORS FOR NEUROTRANSMISSION Prime chemical mediators  Acetylcholine,  Norepinephrine,  Epinephrine ,  Dopamine,  Serotonin,  Histamine,  GABA,  Glycine,  Glutamate

Co-transmitters  Enkephalin  Endorphin,  ATP,  substance P,  neurotensin,  somatostatin,  neuropeptide Y,  vasoactive intestinal peptide (VIP).

PHARMACOLOGICAL CLASSIFICATION OF RECEPTORS Pharmacological family Acetylcholine receptors  Muscarinic M - M1 - M2 - M3  Nicotinic - N1 - N2 Adrenaline receptors  β1  β2  α1  α2

Molecular Super-family   -

Protein-G type receptors Gq Gi Gq Channel type receptors Channel -Na+ Channel-Na+

   

Gs Gi Gq Gi 153

PHARMACOLOGICAL CLASSIFICATION OF RECEPTORS Pharmacological family Glutamate, aspartate receptors  Metatropic  Ionotropic Serotonin receptors (5-HT)  5-HT1 and 5-HT2  5-HT3

Molecular Super-family  Protein-G type receptors  Channel type receptors  Protein-G type receptors  Channel type receptors

154

3.5 MECHANISMS OF INTERACTION DRUGRECEPTOR Ligand • The term ligand applies indistinctly to either the agonist or the antagonist , meaning only any molecule able to bind to the receptor. Mediators • There are natural chemical substances acting as neurotransmitters or hormones. Agonist effect • Agonist drug produces the same effect as does the natural mediator substance. Antagonist effect • Antagonist drug downturns the normal effect produced by a natural mediator substance or reverses the effect.

155

ACTION OF AGONISTS A direct agonist binds to receptor, and the formed complex is initiates the action

D + R  DR active

DIRECT AGONIST

D INDIRECT AGONIST

M+RMR active

Mediator

An agonist acting indirectly lacks affinity with the receptor, thus doesn’t form a complex DR. However, it only avail sufficient concentration of natural mediator that will bind to its receptors and then initiates the action. An indirect agonist is not active molecule per se. 156

ACTION OF ANTAGONISTS A direct antagonist drug binds the receptor and blocks the action; the complex is said inactive.

A + R  AR (inactive complex) DIRECT ANTAGONIST

INDIRECT ANTAGONIST

A M

An antagonist drug acting indirectly doesn’t bind the receptor. It reduces or clears the concentration of the mediator on the biophase. The receptor will remain unbound and thus no action is initiated. 157

NEUROTRANSMISSION Electric transmission Pre-synaptic membrane

M M

M M MM

Chemical transmission M Electrical transmission Post-synaptic membrane 158

Example of direct and indirect action in Sympathetic Nervous System

159

Indirect mechanisms of action

PHARMACOLOGICAL AGENT ACTING INDIRECTLY ON THE NERVE AGONIST

SYNTHESIS

STOCKAGE

ANTAGONIST

I I

LIBERATION

REUPTAKE

METABOLISM

S= stimulates event (Concentration of mediator increases in synaptic cleft) I= inhibits event (concentration of mediator is reduced in synaptic cleft)

160

Other illustration of direct and indirect action: cAMP and cGMP pathways

161

Other illustration of direct and indirect action: cAMP and cGMP pathways Nitric Oxide Receptor (NO)

Guanylylcyclase GTP

Sildenafil (Viagra) Theophilline Dobutamine

Phosphodiesterase GMP ReceptorÎ˛1

Adenylylcyclase ATP

Amrinone

cGMP

Muscle relaxation Vasodilation Bronchodilation Coronodilation

cAMP

Heart contraction

Phosphodiesterase AMP

162

3.6 DOSE- EFFECT RELATIONSHIP The relationship depends on both the drug and the living system screened

163

DOSE- EFFECT RELATIONSHIP Graded response curve

All-or-none response curve

Pressure mmHg

Mortality %

180

100%

50%

ED50 Gradual curve

Dose

LD50 Quantal curve

Log Dose

The effect may be either « gradual » or « quantal » type 164

Quantitative aspects of drug-receptor interaction â&#x20AC;˘ In a graded type of dose-effect relationship, it is assumed that the response of an individual biologic unit increases measurably with increasing concentration of drug. â&#x20AC;˘ In the quantal type, the assumption is made that the individual units of the system respond to their maximum capability or not at all. To explore the relationship dosequantal response we must use many individuals and obtain enumerative data of the number either responding or not responding to each given dose.

165

Quantitative aspects of drug-receptor interaction

• We should consider three variables – Affinity: the product of this reaction becomes the stimulus for the events leading to the effects. – Efficacy: the stimulus is of low or high intensity. – Potency: the lesser the amount of drug required to produce an effect, the greater the potency of the drug.

166

Affinity calculation: application of the law of Mass Action • • • • • •

[L] = concentration of free Drug [RL] = concentration of bound Drug [R] = concentration of free receptors Rt = total concentration of receptors Kd = Dissociation constant Kd represents the concentration at which 50% of receptors are occupied. The inverse (1/Kd) represents the magnitude of the affinity between drug and receptor.

167

Efficacy and Potency calculations Efficacy ranges from zero to 100 % of the maximal biological effect of the system Potency represents the dose needed to obtain 50 per cent maximal response (ED50)

ED50=Kd ; The potency coefficient value pD is the negative log of ED50

168

Spare-receptors concept •

•

The sensitivity of a biologic system to drug depends on the density in receptor binding sites. In patient with hyperthyroidia, the density of -adrenergic receptors is likely increased in the heart and that leads to increasing heart sensitivity to adrenaline and other catecholamines. In the graph, 100% of maximum response is obtained with 70% receptors occupancy. The non occupied fraction of receptors is termed as sparereceptors. 169

Chapter-4 BASIC TOXICOLOGY • Overall, any drug is a poison; the difference with a potent poison lays on the magnitude of active dose and the intensity of the action triggered . (Claude Bernard : experimental pathology,1872). • Each drug elicits characteristic toxicological pattern, and accordingly it may be classified as ‘toxic’, ‘dangerous’ or ‘safe’, depending on its therapeutic index. • The toxic effect is the deleterious effect provoked by a substance and that threatens life. The toxic effects of drugs are foreseeable on the basis of the experimentation done priori during the phases of drug evaluation; they are therefore avoidable insofar as the conditions of advisable use are respected. 170

4.1 TOXICOLOGIC TERMS & DEFINITIONS • TOXICITY, HAZARD, & RISK – Toxicity is the ability of a chemical agent to cause injury. – Hazard is the likelihood that injury will occur in a given situation or setting: the conditions of use and exposure are primary considerations. Humans can safely use potentially toxic substances when the necessary conditions minimizing absorption are established and respected. – Risk is defined as the expected frequency of the occurrence of an undesirable effect arising from exposure to a chemical or physical agent. Estimation of risk makes use of dose-response data and extrapolation from the observed relationship to the expected responses at doses occurring in actual exposure situations.

171

Types of toxicity â&#x20AC;˘ Some toxic effects are unforeseeable and therefore unavoidable. â&#x20AC;˘ The toxic effects can appear of straightaway (acute toxicity) or after one time of more or less long exhibition following the accumulation of small doses repeated for a long time (sub acute or chronic toxicity) . Acute toxicity onset

24 hours

dosage

Single dose

Subacute toxicity

Chronic toxicity

1/10 life expectancy

Long term all life

Fractioned doses

Small repeated doses

172

4.2 Therapeutic Drug Index â&#x20AC;˘ The therapeutic index of a drug is the ratio of the dose that produces toxicity (TD)to the dose that produces a clinically desired or effective response (ED)in a population of individuals.

173

4.3 Adverse Drug Reactions (ADRs) â&#x20AC;˘ ADRs are harmful reactions that appear fortuitously and are unwanted in a therapeutic course time. â&#x20AC;˘ Most drugs produce many effects, and all drugs produce at least two effects. And it is also a truism that no chemical agent can be considered entirely safe. The therapeutic effect is the one that is desired while the other effects unwanted are side-effects. 174

Classification of adverse drug reactions Type-A reactions â&#x20AC;˘ Type-A adverse reactions are those associated to the pharmacological action of the drug. They are foreseeable but unavoidable. Their intensity is proportional to the dose introduced in the body. They are of two classes: categorical reactions and lateral reactions.

Type-B reactions â&#x20AC;˘ The type-B side effects are not associated to the pharmacological effects of the molecule. These are unforeseeable reactions attributable to the individual subject. One also distinguishes two classes for the B-type reactions: allergic reactions and idiosyncratic reactions.

175

Type-A Categorical Side Effects â&#x20AC;˘ Categorical reactions are the reactions that are lined in the extension of the pharmacological action but they are unwanted. They are therefore linked with the major effect of the drug that constitutes the therapeutic indication of the molecule. â&#x20AC;˘ Example: the anticancer effect is gotten by inhibition of cancerous cells division or multiplication. This antimitotic effect is not limited selectively to the only cancerous cells , it also affects the normal cells having an intense mitotic turnover, i.e. the gonad germ-cells and the follicular cells. Cancerous patients will develop loss of hair (alopecia) and secondary azoospermia as categorical side effects. 176

Type-A Lateral side-effects • The absence of specificity in action is here responsible of the lateral side effects that are foreseeable but unavoidable. • Example: when atropine is absorbed , many effects of its inhibitory activity at the acetylcholine receptor become evident. In the stomach the effect of atropine is to decrease the hydrochloric acid secreted ; in the oral mucosa, the action leads to the production of dry mouth; in the eye the atropine increases the diameter of the pupil; • Thus, in case of treatment of the diarrhea by the atropine, the dilation of pupil, the dry-mouth or the possible tachycardia are undesirable lateral effects. On the other hand, at the time of an eye exam in ophthalmology, the mydriatic effect becomes the desired effect while the others are considered side effects.

177

Type-B Allergic Drug reactions â&#x20AC;˘ The allergic reactions don't have any link with the pharmacological activity and are of variable severity. â&#x20AC;˘ The allergic reactions are immunological reactions developing in subjects whose blood contains antibodies as consequence of previous exposure to the chemical concerned or to certain substances structurally related to the immunogenic drug.

178

Type-B Idiosyncratic drug reactions • The idiosyncratic reactions are the unforeseeable undesirable effects, particular to the individuals, as consequence of their hypersensitivity that can be, the most often but not always, bound to the genetic heritage. • The hypersensitivity to the primaquine is the example related to Glucose- 6-phosphate dehydrogenase deficiency. • Polymorphism in drug metabolism. 179

4.4 DRUG ABUSE AND DEPENDENCE • The term drug abuse refers to the excessive and consistent use, usually by self-administration, of any drug without due regard for accepted medical practice. • The vast majority of drugs of abuse are agents that act on the central nervous system to produce profound effects on mood, feeling and behaviour. • The term drug dependence has two distinct and independent components: psychologic dependence and physical dependence. 180

Drug dependence PSYCHOLOGIC DEPENDENCE

PHYSICAL DEPENDENCE

• Psychologic dependence is a condition characterized by an emotional or mental drive to continue taking a drug whose effects the user feels are necessary to maintain his sense of optimal well-being. • The behavior is termed drugseeking behavior or compulsive drug use.

•

Physical dependence is an altered or adaptive physiologic state produced in an individual by the repeated administration of a drug. Physical dependence manifests itself as intense physiologic disturbances called the withdrawal or abstinence syndrome. Physical dependence occurring together with psychologic dependence is a powerful factor in reinforcing the compulsion to continue taking the drug

181

Drug tolerance • The term drug tolerance is a cellular adaptation phenomenon of living systems vis-à-vis of certain drugs, dragging a reduction of the biologic answer when the same doses are absorbed. The tolerance obliges to increase the dose progressively to get the level of previous efficiency ; the organism becomes capable to support more and more amounts of the substance. • Tolerance to a drug can occur very quickly (tachyphylaxis) as in the case of ephedrine), or it gets settled slowly after several repeated doses like that is the case with morphine. • The mechanisms of tolerance can raise from disruptions of the pharmacokinetic parameters (self-induction of the hepatic metabolism) or from the modification of the sensitivity of the receptors. • Tolerance led by a substance can spread to related chemical molecules (crossing tolerance). 182

Chapter-5 BASIC PHARMACOTHERAPY • PRESCRIBING GUIDELINES • DOSING PRINCIPLES • DRUG DRUG INTERACTIONS

183

5.1 PRESCRIBING GUIDELINES •

•

When you will approach the clinical phase of your formation, you will perceive that you hardly know how to prescribe a medicine to your patients nor where to be going to look for the corresponding information. It is in general due to the fact that the courses of pharmacology that you followed or that you will follow are more theoretical than convenient, and that their content is above all about the mechanisms of action, the indications and the side effects of the various products. In pharmacology we go from medicine to the disease. However, in clinic, the prescription follows precisely an inverse stepwise, since one leaves from the diagnosis to arrive to the medicine. Besides, to the considerations of age, sex, the stoutness and the sociocultural features, that are as many elements to take in account in the choice of the treatment. The patients are all different ; not to mention that they personally make themselves an idea of that should be a suitable treatment.

184

PRESCRIBING GUIDELINES â&#x20AC;˘ The prescription is part of a logical deductive process calling on complete and objective data. It is not a "recipe for pancakes", not more is it a matter of an automatic device or a commercial pressure. â&#x20AC;˘ The bad habits of prescription or dispensation are the reason of inefficient or dangerous treatments, an exacerbation or the overtime of the illness, distress and suffering for the patient and elevated cost. 185

VARIABILITY IN RESPONSE ATTRIBUTABLE TO THE PATIENT • BODY WEIGHT AND SIZE • The magnitude of drug response is a function of the concentration of drug attained at a site of action, and this concentration is related to the volume of distribution. For a given drug, the greater the volume of distribution, the lower the concentration of the drug reached in the various fluid compartments of the body mass. – Dose required= (average dose)x(weight of individual kg/ 70 kg)

186

VARIABILITY IN RESPONSE ATTRIBUTABLE TO THE PATIENT • AGE • Some effects of age on the quantitative aspects of drug activity are inseparable from those attributable to size, since the two variables are directly related during the early part of the life. However, age, not size, is the more dominant factor in the variability of drug action in the infant and young child. And the elderly also frequently respond to drugs in a manner that cannot be imputed merely to differences in body weight. • These individuals at the extremes of the life-span are often unusually sensitive to drugs; their responses occur at the far left of the normal distribution and quantal dose-response curves. The apparent increase in sensitivity is associated with changes in rates of absorption, distribution, biotransformation or excretion.

187

VARIABILITY IN RESPONSE ATTRIBUTABLE TO THE PATIENT

188

5.2 Prescribing in infant and young child • A lot of authors warn that the child is not an adult in miniature ; he/she has his/her own features and physiological realities that it is necessary to take in consideration. • The problem of posology to the infantile age is as old as the pediatrics itself. • Some empiric or scientific rules have been established to permit adapting the adult's posology to the child. • The adaptation is based the most often on the weight, age and more lately the body surface area. Posology is the science of determining and understanding drug dosages

189

Prescribing rules in infant and young child â&#x20AC;˘ The rules based on age or the weight don't take in consideration the phenomenon of development of the child. For a same age, the children can greatly differ in size and in weight. Example :

Age Height Weight 10 ans 132.8 cm 27.71 kg 10 ans 147.5 cm 40.78 kg â&#x20AC;˘ Based on age measures out it will be identical for the two children whereas on basis of the weight or the bodi surface the doses are different for the two children. â&#x20AC;˘ On a therapeutic level, it seems that the weight and age don't constitute a satisfactory basis for the individualization of the dose. The calculation based on the body surface appears more valid during the whole life, as much for the adult as for the child.

190

Methods for calculating child doses Formula for adaptation n= age (years at last birthday) ; n*= age in months Correction factor (CF) Author Age span Dose infant= Dose adult x FC CLARK SAGEL

YOUNG COWLING DILLING FRIED

> 2 years old 0-20 weeks 20-52 weeks 1-10 years 10-19 years 2-12 years 2-12 years 2-12 years 0-2 years

Weight of child (kg) / 70 kg (13n+5)/100 (8n+7)/100 (3n+12)/100 (3n-16)/100 n/(n+12) (n+1)/24 (n+1)/20 n*/(150) 191

Posology based on body surface area • Height Surface Weight (cm) (m2) (kg) • • • • 120 cm 1,10 m2 40 kg • • • • 50 cm 0,35 m2 5 kg • • • 25 cm 0,074 m2 1 kg

Dose infant = Dose(adult)x (surface infant /1,8 m2).

• Calculation of BSA 1° Formula of DuBois-DuBois S(m2) = P0.425 x H0.725 x 71,80.10-4 2° Nomogram (Abaque) • Join the weight to the size and read in the middle the corresponding surface

192

MODEL OF PRESCRIPTION FORM • Prescriber particulars • Patient particulars • Medicine particulars – R/ Drug name, strength, form – DT/ Total drug amount – S/ Posology & remarks

• Date and prescriber signature

• Some guidelines impose for controlled substances, strength and quantity must be written in letters and not figures • They cannot be refilled 193

5.3 THERAPEUTIC REGIMEN • The posology should indicate the units of measure to take in ounce, the number of units to manage in 24 hours, the intervals between administration and the total therapeutic dose. • The rational posology must permit to get the therapeutic effect wanted with minimum of risk for treatment failure by under-dosage and poisoning by overdosing. • Some medicines have very narrow margins of safety and need a closer monitoring of blood concentrations. 194

DRUG REGIMEN â&#x20AC;˘ When a drug is repeatedly administered, the concentration in the blood increases until the time where the amount absorbed and the amount eliminated between two administrations is balanced. At the equilibrium time, the concentration regularly oscillates between a minimum and a maximum if the maintenance doses are identical and equally spaced. The level of accumulation depends on the dose, the dosing interval and of the half-life of the drug. 195

DRUG DOSING REGIMENS â&#x20AC;˘

â&#x20AC;˘

The necessary time to reach the steady-state level is independent of the dose; it only depends on the halflife of the drug. In general principle the equilibrium is reached after a time equal to 6 times the half-life of the drug. The therapeutic concentration can be achieved before the 6 times the halflife if the maintenance doses are preceded by a loading dose.

196

Dosage calculation

Dm=Da.(1-e-keĎ&#x201E;)

T1/2= 0.693.Vd/CL

Da= loading dose (mg) Dm= maintenance dose (mg) Ď&#x201E;= interval of administration (hours) F= bioavailability Cl= clearance (ml/min) Vd= volume of distribution (ml/kg) SrCrss= serum creatinine at steady state ( mg/dL

197

THE SIX RIGHTS AND DRUG ADMINISTRATION • Patient well diagnosed • Drug labeled and efficacious for the disease • Therapeutic and individualized dose • Regular time of administration • Correct information given about how to take, side effects, precautions, contra-indications, pregnancy category

1. 2. 3. 4. 5. 6.

Right patient Right drug Right dose Right route Right time Right documentation

198

Complementary/Alternative Medicine (CAM) • Herbal therapy is part of a group of nontraditional therapies commonly known as complementary/alternative medicine • Complementary therapies are therapies such as relaxation techniques, massage, dietary supplements, healing touch, and herbal therapy that can be used to “complement” traditional health care. • Alternative therapies, on the other hand, are therapies used in place of or instead of conventional or Western medicine. 199

5.4 DRUG- DRUG INTERACTIONS • It has been estimated that the average hospitalized patient may receive as many as six to ten different drugs during his confinement. In chronic disease states such as epilepsy, diabetes and heart disease, when the patient contracts another illness, the conjoint therapeutic administration of several drugs may be mandatory. • Whatever the rationale for administering several drugs concurrently, the question arises of how these drugs may affect each other’s actions. 200

Drug Interactions: Definition • “The pharmacologic or clinical response to the administration of a drug combination different from that anticipated from the known effects of the two agents when given alone” • Tatro DS (Ed.) Drug Interaction Facts. J.B. Lippincott Co. St. Louis 1992

201

Types of Drug Interactions • Pharmacokinetic • -What the body does with the drug • -One drug alters the concentration of another by altering its absorption, distribution, metabolism, or excretion Usually (but not always) mediated by cytochrome P450 • (CYP) • Pharmacodynamic • -Related to the drug’s effects in the body -One drug modulates the pharmacologic effect of another: additive, synergistic, or antagonistic

202

Pharmacodynamic Drug Interactions • • • • • • • • • • •

Synergistic combinations -Pharmacologic effect > than the summation of the 2 drugs -Beneficial: aminoglycoside + penicillin -Harmful: barbiturates + alcohol Antagonism -Pharmacologic effect < than the summation of the 2 drugs -Beneficial: naloxone in opiate overdose -Harmful: zidovudine + stavudine Additivity -Pharmacologic effect = the summation of the 2 drugs -Beneficial: aspirin + acetaminophen -Harmful: neutropenia with zidovudine + ganciclovir 203

Pharmacodynamic Drug Interactions • Idiosyncratic (Type B drug interactions) • Occur rarely and unpredictably • The reaction is not a simple extension of the drug’s • pharmacologic activity; usually immune mediated • -Example: meperidine + MAO inhibitor – Concurrent use of meperidine and MAO inhibitors may result in hypertensive crisis, hyperpyrexia and cardiovascular system collapse, and may be fatal. 204

Synergism and Antagonism • Synergism or Antagonism refer to different situations in which the combined effect of two (or more) drugs acting simultaneously is greater or less than the effect of each agent given alone. • Let us consider two drugs D1 et D2 acting at the same receptor. 1.Emax 2.Emax ED1D2 = ———— + ————— 1 + Kd1/D1 1 + Kd2/D2 ED1D2 1.D1.Kd2 + 2.D2.Kd1 ——— = ——————————— Emax Kd1.Kd2 + D1.Kd2 + D2.Kd1

205

Synergism or Antagonism • The term additive effect is usually used in those cases in which the combined effect of two drugs acting by the same mechanism is equal to that expected by simple addition. (of course the magnitude of the combined effect must be within the capacity of the system to respond.) • In synergism, the joint effect of two drugs is greater than the algebraic sum of their individual effects. In synergism the intensity of the effect may be potentiated or the duration of action prolonged. • The term Potentiating is usually reserved for cases in which two drugs act at different sites and one drug, the synergist, increases the effect of the second drug by altering its biotransformation, distribution or excretion.

• Any time the conjoint effect of two drugs is less than the sum of the effects of the drugs acting separately, the phenomenon is called drug antagonism. 206

Synergism • • • •

1.1. Additive Effect 1.2. Competitive Synergy 1.3. Competitive Dualism 1.4. Potentiating

207

Competitive synergism • Efficacy 1 is comparable to 2 and the two drugs act at the same receptor. • The dose-effect curve of the combined effect moves to the left of each drug given alone.

208

Competitive dualism •

•

If 1 significantly greater than 2 (case of D2 is partial agonist), and the two drugs act at the same receptor, the combined effect is either greater or lesser than the effect of D1 given alone. For some concentrations the combination exhibits synergism, but at some concentrations the antagonism occurs. There is one concentration or dose of D1 for which the combined effect is equal to the effect of D1 given alone. This standpoint is called the dualism point. To the left of the dualism point, synergism is exhibited, while to the right side the antagonism is elicited.

209

Potentiating • If the two drugs act at different sites and one drug, the synergist, increases the effect of the second drug by altering its biotransformation, distribution or excretion, the intensity of the effect may be potentiated or the duration of action prolonged. Example-1: • Eserine potentiates the effects of acetylcholine in inhibiting the enzyme acetylcholinesterase. The potentiating is said direct because the same system is concerned (parasympathetic system).

• •

Example-2: Atropine is a parasymatholytic agent and noradrenaline is a sympathomimetic agent. The hypertensive effect of noradrenaline is potentiated by atropine in abolishing the vagal reflex bradycardia in the heart. The potentiation is said indirect since the two drugs act on different systems. Example-3 Chlorpromazine is the prototype of substances capable of potentiating many drugs by unknown mechanisms. 210

ANTAGONISM â&#x20AC;˘ There are four mechanisms by which one drug may oppose the action of another, and different terminology is used to distinguish among them. â&#x20AC;˘ The four types are: 1.1 pharmacological or competitive antagonism, 1.2 physiological or noncompetitive antagonism, 1.3 biochemical antagonism 1.4 chemical antagonism. 211

Pharmacological antagonism â&#x20AC;˘ When an antagonist A reduces the effect of an agonist D by preventing it from combining with its receptor, the interaction of the two drugs is known as pharmacological antagonism or competitive antagonism. Examples: â&#x20AC;˘ Diphenylhydramine and histamine (H1 receptor) â&#x20AC;˘ Atropine and acetylcholine (M receptor)

The potency is reduced but the efficacy may be restored. The opposition is reversible.

212

Physiological antagonism â&#x20AC;˘ Physiological or functional antagonism is observed when two agonists, acting at different sites, counterbalance each other by producing opposite effects on the same physiologic function. Examples: â&#x20AC;˘ The effects of histamine of blood pressure (vasodilatation) and on bronchus (bronchoconstriction) can be offset by adrenaline.

Both the potency and the efficacy are reduced. The opposition not reversible, but the effects are balanced.

213

Biochemical antagonism •

Biochemical antagonism can be thought of as the opposite of synergism. This type of antagonism occurs whenever one drug indirectly decreases the amount of a second drug that would otherwise be available to its site of action in the absence of the antagonist. Thus a drug which increases the rate of biotransformation or excretion of an agonist, or competes with the agonist’s transport to its site of action is termed a biochemical antagonist.

Examples: • Inducers of microsomal enzymes such as phenobarbital.

214

Chemical antagonism • Chemical antagonism is simply the reaction between an agonist and an antagonist to form an inactive product . • The agonist is inactivated in direct proportion to the extent of chemical interaction with the antagonist.

Examples: • The anticoagulant effect of the strong, negatively charged macromolecule heparin is antagonized when the drug combines with strongly basic dyes (toluidine blue) or basic proteins (protamine). • Neutralization of excess gastric acid by the antacid drugs such as aluminum hydroxide or sodium bicarbonate.

215

SECTION 2-PHARMACOLOGY OF THE PERIPHERAL NERVOUS SYSTEM PERIPHERAL NERVOUS SYSTEM

216

2.1 INTRODUCTION The Neuron, constitutive unit of the Nervous System

Dendrite; Soma; Nucleus; Myelin sheath; Schwann cell; Axon; Node of Ranvier; Axon Terminal 217

The Innervations Map

218

Peripheral nervous system

219

Peripheral Neurotransmitters & Receptors

220

Peripheral Neurotransmitters & Receptors

221

Sympathetic and Parasympathetic Effects of the autonomous system SYMPATHETC MYDRIASIS

Eye Iris

Radial Muscle 1 Circular Muscle CiliaryMuscle 2

Mydriasis relaxation

PARASYMPATIC MIOSIS

M3 M3

Miosis Accommodation 222

Sympathetic and Parasympathetic Effects of the autonomous system

Heart Sinoatrial node Pacemaker cell Myocardium

1 1 1

Rapid rate (tachycardia) Stimulation Contraction (+ inotrope)

M2 M2

Slow rate (bradycardia) Atrial relax (- inotrope)

223

Sympathetic and Parasympathetic Effects of the autonomous system

Blood vessels Viscera, skin vessels Splanchnic vessels Skeletal muscles

1 2 D1 2

Vasoconstriction Vasodilation Vasodilation Tremor

M3 ?

Vasodilation

224

Sympathetic and Parasympathetic Effects of the autonomous system

Bronchi Smooth Muscle Secretory gland

ď ˘2 -

Bronchodilation -

M3 M3

Bronchoconstriction Increase of mucus production

225

Sympathetic and Parasympathetic Effects of the autonomous system

Genital system Uterus gravid

Penis

2 

Relaxation (tocolytic effect) Contraction (labor stimulation)

Contraction



Ejaculation

Erection

226

Sympathetic and Parasympathetic Effects of the autonomous system

Gastro-intestinal tract Smooth Musculature Sphincter musculature Acid Secretion

,2 1 -

{block of defecation} Relaxation Closing -

M3 M3 M3

{Defecation, diarrhea} Contraction Opening Stimulation of HCl

Salivary Glands



Non rich saliva (dry mouth)

Saliva production viscous 227

Sympathetic and Parasympathetic Effects of the autonomous system

Urinary tract Bladder Detrusor muscle Sphincter muscle

{Urine retention}

{Urination}

2 1

Relaxation Closing

M3 M3

Contraction Opening

Juxtaglomerular apparatus

1

Secretion of renin

228

Sympathetic and Parasympathetic Effects of the autonomous system

Liver

 2

Gluconeogenesis (hypoglycemia) Glycogenolysis (hyperglycemia)

Pancreas

2 2

Insulin secretion inhibited Insulin secretion enhanced

229

2.3 Drugs acting through PNS • AUTONOMIC DRUGS – ADRENERGICS: SYMPATHETIC ACTING • Sympathomimetic agents (agonists) • Sympatholytic agents (antagonists)

– CHOLINERGICS : PARASYMATHETIC ACTING • Parasympathomimetic agents (agonists) • Parasympatholytic agents (antagonists)

– CHOLINERGICS : GANGLIA ACTING • Gangliostimulant agents (agonists) • Ganglioplegic agents (antagonists)

• SOMATIC DRUGS – CHOLINERGICS : MUSCLOSKELETAL ACTING • Antimyasthenia agents (depolarizing agonists) • Muscle relaxant agents (depolarizing and non depolarizing antagonists)

230

Selectivity of Adrenergic Drugs Alpha- Beta Acting

Alpha- Acting

αβ

α1 α2 β1 β2 β3

α1 α2 β1

α1 α2

Beta-Acting

α1

α2

β1 β2

DIRECT AGONISTS OR ANTAGONISTS Non Selective or Selective

β1

β2

231

Selectivity of Cholinergic Drugs MIXED ACTION

MUSCARINIC ACTION

M=N

NICOTINIC ACTION

M>N

M1 M2 M3

DIRECT AGONISTS OR ANTAGONISTS Non Selective or Selective 232

2.3.1 Drugs of the Sympathetic System Tyrosine AXON

SYNTHESIS

Tyrosine Tyrosine hydroxylase

DOPA

DOPA-decarboxylase

Dopamine

STOCKADE

-hydroxylase

2

Noradrenaline Noradrenaline

PRESYNAPTIC INDIRECT ACTION REUPTAKE METABOLISM

POSTSYNAPTIC DIRECT ACTION

RELEASE

NA ACTION

1 1, 2

233

Direct Sympathomimetics & Sympatholytics Prototype * =with indirect action ; a=anesthetic ; p=partial agonist 1 2 1 2

1 2 1

1 2

1

2

Agonists

Epinephrine Ephedrine*

Norepinephrine

Etilephrine* Mephentermine* Phenylephrine* Metaraminol Metoxamine

Naphazoline Oxymetazoline Tramazoline Xylometazoline

Clonidine

INDICATION agonists

Hypotension Asthma Nasal decongestion

Hypotension Heart failure

Hypotension

Nasal Decongestion Rhinitis

Hypertension

Antagonists

Carvedilol Labetalol (ap)

Dibenamine Dihydroergotamine Phentolamine Phenoxybenzamine

Doxazosine Prazosine Alfuzosine

Yohimbine Piperoxone

INDICATION antagonists

Hypertension

Hypertension Pheochromocitome

Hypertension Benin prostate hyperplasia

Aphrodisiac

234

Direct Sympathomimetics & Sympatholytics Prototype * =with indirect action ; a=anesthetic ; p=partial agonist 1 2

1

2

Agonists

Isoprenaline (isoproterenol)

Dobutamine Prenalterol

Fenoterol Ritodrine Salbutamol Salmeterol Terbutaline

INDICATION agonists

Heart failure Asthma

Heart failure

Asthma Tocolytic effect

Antagonists

Propranolol (a) Sotalol (p) Pindolol (p) Nadolol Timolol

Acebutolol Atenolol Betaxolol Esmolol Metoprolol

Butoxamine

INDICATION antagonists

Hypertension

No indication

235

Indirect Acting Sympathetic Neuroblockers Neuroblockers

Mode of inhibition

L-tyrosine Metyrosine DOPA

Inhibition of Synthesis Metyrosine -Methyl-dopa Disulfiram Inhibition of Stockade Reserpine Inhibition of Release Bethanidine Bretylium Debrisoquine Guanadrel Guanetidine

Disulfiram Dopamine Reserpine

Guanetidine

-blocker

-blocker

Direct Antagonists 236

2.4 Drugs of the Parasympathetic System Choline AXON

SYNTHESIS

Choline ACh-CoA

Enzyme

STOCKADE

Acetylcholine PRESYNAPTIC INDIRECT ACTION

Acetylcholine

RELEASE METABOLISM

ACh ACTION

POSTSYNAPTIC DIRECT ACTION

M1, M2, M3 237

Direct cholinergic agents *

Activity M>N

Toxic, no clinical use

M1M2M3NN NM M1M2M3

Agonists

Acetylcholine Carbachol Bethanechol* Methacholine* Pilocarpine*

Muscarine* Aceclidine Oxtremorine

INDICATION agonists

Myasthenia Glaucoma Ileus paralyticus

Dry mouth

Antagonists

Atropine Ipratropium Scopolamine Metscopolamine Tropicamide Mepenzoate Oxyphencyclimine

Pirenzepine Telenzepine

Tripitramine

Darifenacin

INDICATION antagonists

Diarrhea Asthma Vomiting Peptic ulcer

Peptic ulcer

Bradycardia

Diarrhea Asthma Vomiting Peptic ulcer 238

Muscarinic â&#x20AC;&#x201C;vs- Atropinic Effects System

Muscarinc effects

Atropinic Effects

Bradycardia

Tachycardia

Miosis

Mydriasis and cycloplegia

Pulmonary system

Bronchoconstriction Stimulation of secretions

Bronchodilation Inhibition of secretions

Salivary gland

Stimulation of secretion

Dry mouth

Purgation Stimulation of HCl

Constipation Inhibition of acid secretion

Atropinic fever

Contraction

Relaxation (tocolytic effect)

Muscle rigidity Tremors Memory

Sedation Stimulation of respiration Suppression of rigidity Motionless Senescence

Cardiovascular Eye

Gastrointestinal system Metabolism Uterus CNS

239

Direct cholinergic agents NN NM

Agonists Depolarizing

Nicotine

Succinylcholine (suxamethonium)

Lobeline

INDICATION agonists

Smoking

Anesthesia (muscle relaxant)

Smoking withdrawal

Antagonists Non depolarizing

Tubocurarine Pancuronium Metocurine Gallamine Alcuronium Atracurium Vecuronium

Trimethaphan (Arfonad速) Hexamethonium (Inversine速) Decamethonium Mecamylamine Pempidine Pentamethonium

INDICATION antagonists

Anesthesia (muscle relaxant)

240

Direct Ganglionic Acting Drugs Spectrum Ganglia Activity NN

Depolarizing agents (Agonists) Nicotine Lobeline

Non Depolarizing agents (Antagonists) Trimethaphan (Arfonad速) Hexamethonium (Inversine速) Decamethonium Mecamylamine Pempidine Pentamethonium

241

2.5 Drugs of the Somatic System Spectrum Depolarizing agents Skeletal muscle Succinylcholine (suxamethonium) Activity NM

Non Depolarizing agents Tubocurarine Pancuronium Metocurine Gallamine Alcuronium Atracurium Vecuronium Hexafluornium

242

2.6 Indirect Acting Cholinergic Drugs 1) Neuroblockers Choline Acetylcholine

Hemicholiniu m

Vesamicol

Ach Saxitoxin

Botilinum Toxin AchE metabolism

M-receptors

Ach

2) ANTICHOLINESTERASES Aminoalcohols -Ambenonium -Edrophonium -Neostigmine -Physostigmine -Pyridostigmine Organophosphates -Echothiophate -Isofluorophate -Malathion 3) CHOLINESTERASE ACTIVATORS -Pralidoxime

N-receptors 243

MUSCLE RELAXANTS Depolarizing relaxants

Non depolarizing relaxants

Muscolotrope relaxants

Succinylcholine (suxamethonium)

Tubocurarine Dantrolene Pancuronium Metocurine Gallamine Alcuronium Atracurium Vecuronium Hexafluornium Botox: is a drug made from a toxin produced by the bacterium Clostridium botulinum. Itâ&#x20AC;&#x2122;s the same toxin that causes a life-threatening type of food poisoning called botulism. Small doses are used to treat health problems, including: cervical dystonia, blepharospasm (uncontrollable blinking,), strabismus (misaligned eyes), severe underarm sweating, temporary removal of facial wrinkles. Botox injections work by weakening or paralyzing certain muscles or by blocking certain nerves. The effects last about three to four months. 244