This is an antagonistic situation because the antibiotic will less efficiently be absorbed in the presence of the antacid.
ANTIBACTERIAL THERAPY The goal of antibacterial therapy is to be selectively toxic. This means that the drug is toxic to the organism but not to the host. It generally also means that the drug will harm prokaryotes but not eukaryotes. Every antibacterial drug has a specific mode of action against the organism. It can attack the cell wall, the plasma membrane, the ribosomes, DNA synthesis, or the metabolic pathways of the organism. Examples of drugs that attack the cell wall synthesis include penicillins and bacitracin. Protein synthesis in the ribosomes is affected by aminoglycosides, macrolides, and lincosamides. Membranes are disrupted by polymyxin B and daptomycin. Nucleic acid synthesis is affected by fluoroquinolones and rifamycin. Folic acid synthesis is affected by trimethoprim and sulfonamides. There are also drugs that affect the synthesis of ATP and mycolic acid. The first antibiotic known in modern times was penicillin. It belongs to the beta-lactam class of antibiotics, which also includes monobactams, carbapenems, and cephalosporins. Beta-lactams affect the synthesis of the bacterial cell wall because it prevents cross-linking of the peptidoglycan layer. These tend to work better on grampositive organisms. Penicillin is a natural antibiotic. Amoxicillin and ampicillin are aminopenicillins synthesized from natural penicillin. Methicillin is also semi-synthetic. Cephalosporins are also beta-lactams with slightly different chemical properties. It is less resistant to the beta-lactamase enzymes that some organisms secrete. There are many generations of cephalosporins that differ in their spectrum of activity. First generation cephalosporins are the most broadly acting of these drugs, while a new fifth generation cephalosporin is only active against MRSA or methicillin-resistant Staphylococcus aureus. Aztreonam is the only monobactam and it is only active against gram-negative organisms.
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