Aminoglycosides such as gentamicin are increasingly given as a single high daily dose rather than divided doses. Which pharmacodynamic property best justifies this strategy?

• A They produce a significant post-antibiotic effect, allowing bactericidal activity to persist after serum levels have fallen ✓
• B They exhibit time-dependent killing, so prolonged low levels are optimal
• C Their nephrotoxicity correlates directly with peak serum concentration rather than total exposure
• D They require a trough level above the MIC throughout the dosing interval

Explanation

Aminoglycosides show concentration-dependent killing with a prolonged post-antibiotic effect, meaning bacterial growth remains suppressed for hours even after serum levels drop below the MIC. B high peak therefore permits a long drug-free interval without loss of efficacy. Nephrotoxicity arises from saturable cortical tubular uptake, so giving one large dose avoids the repeated accumulation seen with divided dosing, which contradicts option C. Their killing is not time-dependent, and trough suppression of toxicity argues against maintaining troughs above MIC.

Reference: Katzung Basic and Clinical Pharmacology, 15th ed.

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