A blood culture from a septic patient grows MRSA. The isolate is tested and shows a vancomycin MIC of 4 mcg/mL (hVISA phenotype). The MOST clinically relevant implication is:
- A This MIC indicates full sensitivity and standard dosing of vancomycin is sufficient
- B The isolate is resistant to daptomycin but sensitive to linezolid
- C Vancomycin will likely fail therapy due to the 'MIC creep' phenomenon and AUC/MIC target attainment failure ✓
- D Beta-lactam antibiotics remain the preferred treatment for hVISA
Correct answer: C. Vancomycin will likely fail therapy due to the 'MIC creep' phenomenon and AUC/MIC target attainment failure
Explanation
Heteroresistant VISA (hVISA) with vancomycin MIC of 4 mcg/mL places the isolate in the intermediate category. The current IDSA/ASHP guidelines recommend therapeutic drug monitoring using AUC/MIC targeting (AUC 400-600 mg·h/L) rather than trough-only monitoring. When MIC is ≥2, achieving adequate AUC/MIC ratios requires very high doses that risk nephrotoxicity, making vancomycin clinically unreliable. Alternative agents such as daptomycin (for non-pulmonary infections) or linezolid should be considered. Beta-lactams cannot cover MRSA (except ceftaroline).
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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