A 35-year-old patient with Gram-negative sepsis is treated with meropenem. Which pharmacokinetic/pharmacodynamic (PK/PD) parameter best predicts bactericidal efficacy of carbapenems?
- A Time above MIC (T > MIC) — percentage of dosing interval the drug concentration exceeds MIC ✓
- B Peak concentration to MIC ratio (Cmax/MIC) > 10
- C Area under the concentration-time curve to MIC ratio (AUC/MIC) > 125
- D Maximum concentration achieved at the infection site (tissue peak)
Correct answer: A. Time above MIC (T > MIC) — percentage of dosing interval the drug concentration exceeds MIC
Explanation
Beta-lactams including carbapenems exhibit time-dependent bactericidal activity: their killing depends on the duration that free drug concentration remains above the MIC (T>MIC), not on peak concentrations. An optimal T>MIC of 40–70% of the dosing interval is targeted. This is why carbapenems are often given as extended or continuous infusions for highly resistant organisms. Cmax/MIC predicts efficacy for concentration-dependent drugs (aminoglycosides, fluoroquinolones); AUC/MIC for vancomycin and fluoroquinolones.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
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Written and medically reviewed by the StethoPrep medical team.