A 60-year-old man with nosocomial pneumonia caused by Pseudomonas aeruginosa is started on once-daily extended-interval gentamicin. Which pharmacodynamic index best predicts the antibacterial efficacy of aminoglycosides?

• A Ratio of peak concentration to MIC (Cmax/MIC) ✓
• B Ratio of 24-hour area under the curve to MIC (AUC0-24/MIC)
• C Time that plasma concentration remains above the MIC (T > MIC)
• D Ratio of trough concentration to MIC (Cmin/MIC)

Explanation

Aminoglycosides show concentration-dependent bactericidal killing plus a post-antibiotic effect, so efficacy correlates best with the peak concentration to MIC ratio, with a target of roughly 8 to 12. This is the rationale for once-daily high-dose administration, which also reduces nephrotoxicity by limiting drug uptake into proximal tubular cells. Time above MIC governs beta-lactams, and AUC/MIC governs vancomycin and fluoroquinolones, making those indices wrong for this class.

Reference: Goodman and Gilman's The Pharmacological Basis of Therapeutics, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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