Question
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- (a) Mention different groups of penicillins with examples. ( 5 mark(s)
- (b) Explain mechanism of action of penicillins ( 3 mark(s)
- (c) What are uses and adverse effects of Amoxicillin. 4 mark(s)
Answer
a) Groups of penicillins, with examples
| Group | Examples |
|---|---|
| Natural penicillins | Penicillin G (IV/IM), Penicillin V (oral) |
| Antistaphylococcal (beta-lactamase-resistant) | Methicillin, Cloxacillin, Dicloxacillin, Nafcillin |
| Aminopenicillins (extended-spectrum) | Ampicillin, Amoxicillin |
| Antipseudomonal (extended-spectrum) | Piperacillin, Ticarcillin |
b) Mechanism of action All penicillins structurally resemble the terminal D-alanyl-D-alanine of the peptidoglycan precursor, and bind covalently to penicillin-binding proteins (transpeptidase enzymes that normally cross-link peptidoglycan strands) — irreversibly inhibiting this cross-linking. The resulting cell wall is structurally weakened, and in a growing/dividing bacterium, osmotic lysis follows (bactericidal, most effective against actively dividing organisms). Selective toxicity is essentially absolute, since human cells have no cell wall/PBP target at all.
c) Amoxicillin — uses and adverse effects Uses: respiratory tract infections, urinary tract infections, H. pylori eradication (triple therapy), otitis media, often combined with clavulanic acid to restore activity against beta-lactamase-producing organisms.
Adverse effects: hypersensitivity reactions (including anaphylaxis), diarrhea/GI upset, and a characteristic non-allergic maculopapular rash when given in the presence of infectious mononucleosis (a distinctive, frequently examined point).