Meta-Analysis: Vancomycin Treatment Failures for MRSA Bacteremia Based on MIC Determined by E-test

Area of Science:

• Infectious Diseases
• Pharmacology
• Clinical Microbiology

Background:

• Vancomycin is a critical antibiotic for treating serious infections caused by methicillin-resistant Staphylococcus aureus (MRSA).
• The clinical significance of MRSA isolates with vancomycin minimum inhibitory concentrations (MICs) between 1.5 and 2 µg/mL remains uncertain regarding treatment success.

Purpose of the Study:

• To evaluate vancomycin failure rates in patients with MRSA bacteremia based on different vancomycin MIC thresholds.
• Specifically compare failure rates for MICs <1.5 versus ≥1.5 µg/mL and ≤1 versus ≥2 µg/mL.

Main Methods:

• A systematic literature search was performed using relevant Medical Subject Headings (MeSH) terms.
• Included human studies published in English that reported vancomycin failure rates (defined as mortality) in patients with MRSA bacteremia and associated vancomycin MICs determined by E-test.
• Data from 13 studies involving 2955 patients were extracted and analyzed using a random-effects model due to high heterogeneity.

Main Results:

• Analysis of 12 studies (2861 patients) using an MIC cutoff of 1.5 µg/mL showed failure rates of 34.8% for MIC <1.5 µg/mL and 31.7% for MIC ≥1.5 µg/mL (OR=0.72, P=0.08).
• Analysis of 6 studies (728 patients) using cutoffs of ≤1 and ≥2 µg/mL revealed failure rates of 87/384 (22.7%) and 102/344 (29.7%), respectively (OR=0.61, P=0.10).
• No statistically significant difference in vancomycin treatment failure was observed between the compared MIC groups.

Conclusions:

• Vancomycin minimum inhibitory concentration (MIC) alone may not be a reliable sole predictor of vancomycin treatment failure in MRSA bacteremia.
• Further research may be needed to identify optimal therapeutic strategies for MRSA infections with elevated vancomycin MICs.