Which pharmacodynamic parameter best predicts the bactericidal efficacy of fluoroquinolones and is therefore used to optimize their dosing?

• A AUC/MIC ratio (AUIC) ✓
• B Time above MIC (T>MIC)
• C Peak concentration/MIC ratio (Cmax/MIC)
• D Trough concentration/MIC ratio

Explanation

Fluoroquinolones exhibit concentration-dependent killing with a significant post-antibiotic effect; their bactericidal efficacy correlates best with the AUC/MIC ratio (also called AUIC — area under the inhibitory curve). An AUC24/MIC ≥125 for gram-negative organisms is the target for efficacy and resistance suppression. This is distinct from beta-lactams (T>MIC predicts efficacy) and aminoglycosides (Cmax/MIC predicts efficacy). Optimization using AUC/MIC guides once-daily fluoroquinolone dosing strategies.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

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