A 58-year-old man with enterococcal endocarditis is started on intravenous ampicillin plus gentamicin. The pharmacological basis for adding gentamicin to ampicillin is:
- A Gentamicin prevents emergence of beta-lactamase producing mutants
- B The combination prevents binding of penicillin-binding proteins
- C Cell wall damage by ampicillin enhances aminoglycoside entry into the bacterium ✓
- D Gentamicin extends the serum half-life of ampicillin
Correct answer: C. Cell wall damage by ampicillin enhances aminoglycoside entry into the bacterium
Explanation
Aminoglycosides enter bacteria by oxygen-dependent active transport that is enhanced when the cell wall is disrupted. Ampicillin damages the peptidoglycan wall, allowing greater gentamicin influx, producing true synergistic killing. This combination is standard for enterococcal endocarditis. The distractor in option D is killed by the fact that gentamicin has no effect on ampicillin pharmacokinetics; the benefit is purely bacteriological synergy at the bacterial surface.
Reference: Katzung Basic and Clinical Pharmacology, 16th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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