Marc Imhotep Cray, M.D.
Cough Cough—forceful release of air from lungs—is a sudden, often involuntary reflex and a major defense mechanism Airway irritation activates reflex, which forcefully removes irritants, by stimulating airways, which then activates afferent nerves going from respiratory passages through vagus nerve to medulla Activated cough receptors in medulla drive a reflex that initiates inspiration (2.5 L of air) increases contraction of diaphragmatic, abdominal, and intercostal (rib) muscles increases lung pressure and emits air and irritants (at 100 mph)
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Cough (2) Coughs triggered by drainage of mucus from nasal passages into airways are treated with cough suppressants (antitussives) Infection-related coughs (eg, in bronchitis) last for approximately 2 weeks Persistent, chronic coughs (eg, in smokers) must be evaluated Coughs occurring with blood, chest pain, shortness of breath, weight loss, or dyspnea may indicate serious disease Coughs in infants may indicate a serious lung disorder
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Etiology of Chronic Cough With a Normal Chest Radiograph Cause
Prevalence
Postnasal drip
28-41%
Asthma
24-33%
GERD
10-21%
Chronic bronchitis Postinfectious (often, viral URI) bronchial hyperresponsiveness
5-10% 10%
Bronchiectasis
4%
ACE inhibitors, tracheomalacia, eosinophilic bronchitis, psychogenic, etc
5%
Redrawn after Raffa RB. Netter's Illustrated Pharmacology, Updated Ed. Elsevier, 2014
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Causes of Chronic Cough With Abnormal Chest Radiograph
Marc Imhotep Cray, M.D.
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Cough Suppressants (Antitussive Agents) Cough suppressants are opioids that reduce sensitivity of central cough receptors to peripherally activated afferents Receptor desensitization disrupts reflex and minimizes coughing Opioids include opiates (morphine and drugs derived from opium poppy plant, such as hydromorphone, hydrocodone, and codeine) and synthetic drugs that mimic effects of morphine Opioids desensitize central cough receptors, reduce airway mucous secretion, and alter mucous composition
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Antitussive Agents (2) Opioids also produce many adverse effects, including analgesia addiction sedation euphoria respiratory depression nausea & vomiting and Constipation Doses of opioids needed to suppress cough are lower than doses that evoke most of undesirable effects, particularly analgesia and addiction Dextromethorphan, a morphine derivative and glutamate antagonist, suppresses cough center and has fewer adverse effects than other opioids, which accounts for its popularity in over-the counter preparations Marc Imhotep Cray, M.D.
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Other Cough Suppressants Benzonatate [Tessalon] Benzonatate is a glycerol derivative chemically similar to procaine Benzonatate reduces activity of peripheral cough receptors and also appears to reduce threshold of central cough center Diphenhydramine Diphenhydramine is an H1-receptor antagonist; however, antitussive activity is probably not mediated at this receptor Diphenhydramine acts centrally to decrease sensitivity of the cough center to afferents
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Further study: eLearning: Unit 7: Drugs Used In Disorders Of The Respiratory System. In: Digital Guidebook 2015 Integrated Scientific and Clinical Pharmacology IVMS MedPharm Cloud Folder Notes: Drugs Used In Disorders Of The Respiratory System Notes Autacoids, Ergots, Anti-inflammatory Agents, and Immunosuppressive Agents Notes o Histamine and its Antagonists o Eicosanoids
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