A fluoroquinolone is prescribed for a patient. Which pharmacodynamic index best predicts its bactericidal efficacy?
- A Time above MIC (T > MIC)
- B Trough concentration to MIC ratio (Ctrough/MIC)
- C Peak concentration to MIC ratio (Cmax/MIC) and AUC/MIC ratio ✓
- D Half-life relative to MIC (t½/MIC)
Correct answer: C. Peak concentration to MIC ratio (Cmax/MIC) and AUC/MIC ratio
Explanation
Fluoroquinolones show concentration-dependent killing; their bactericidal activity correlates best with peak/MIC (Cmax/MIC ≥ 10) and AUC/MIC (AUC24/MIC ≥ 125 for gram-negatives). Time-dependent killing (T>MIC) governs beta-lactams and vancomycin. Trough levels correlate with efficacy for aminoglycosides in some models, and half-life alone is not a PD index.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
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