Compare and contrast bw ampicillin and amoxicillin Keep it simple and short For a 5 marker
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Ampicillin vs. Amoxicillin - Comparison (5 Marks)
Both are aminopenicillins (extended-spectrum penicillins) with a broad-spectrum bactericidal action against gram-positive and gram-negative organisms. Their similarities and differences:
Similarities
- Same mechanism: Inhibit bacterial cell wall synthesis by binding Penicillin-Binding Proteins (PBPs)
- Same spectrum: Streptococci, enterococci, H. influenzae (non-beta-lactamase producing), E. coli, Salmonella, Proteus
- Both are beta-lactamase sensitive (inactivated by beta-lactamases)
- Similar half-life (~80 min) and protein binding (~20%)
- Both require dose adjustment in renal failure
Key Differences
| Feature | Ampicillin | Amoxicillin |
|---|---|---|
| Oral absorption | ~40% (incomplete) | 75-90% (more complete) |
| Effect of food | Reduced by food | Not affected by food |
| Peak plasma conc. | Lower after oral dose | 2-2.5x higher than ampicillin (same dose) |
| Routes available | Oral, IV, IM | Oral (primarily) |
| Shigellosis | Effective | Less effective |
| Frequency of dosing | 4 times daily | 3 times daily (more convenient) |
| Diarrhea (side effect) | More common | Less common (due to better absorption) |
| Preferred use | Serious IV infections (meningitis, septicemia, enterococcal endocarditis) | Oral outpatient infections (otitis media, sinusitis, RTIs, UTIs, H. pylori) |
| Combination partner | + Sulbactam (IV) | + Clavulanate (oral - co-amoxiclav) |
Key Take-Home Point
Amoxicillin is preferred over ampicillin for oral use because of better bioavailability, food independence, lower diarrhea incidence, and less frequent dosing. Ampicillin is preferred intravenously for severe infections. The only exception where ampicillin is superior orally is shigellosis.
(Sources: Goodman & Gilman's Pharmacological Basis of Therapeutics; Katzung's Basic & Clinical Pharmacology, 16th Ed.)
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