American Board of Internal Medicine (ABIM) Certification Practice Exam

What is the minimum inhibitory concentration (MIC) of vancomycin that indicates daptomycin as a better option for treating MRSA?

1. 1 µg/mL

2. 2 µg/mL

3. 3 µg/mL

4. 4 µg/mL

The correct answer is: 2 µg/mL

The minimum inhibitory concentration (MIC) of vancomycin is crucial in determining the appropriate treatment for infections caused by methicillin-resistant Staphylococcus aureus (MRSA). When the MIC for vancomycin is at or above a specific threshold, it may indicate that the standard treatment with vancomycin is less effective, and alternative agents such as daptomycin should be considered. An MIC of 2 µg/mL is significant because it marks a point where vancomycin may no longer be optimal for treating MRSA infections. At this level, there is a higher risk of treatment failure, and therefore, daptomycin, which can be more effective in clearing MRSA at higher MICs, becomes a better therapeutic choice. If the MIC were lower than this threshold, vancomycin could still be an effective treatment option. Conversely, higher levels such as 3 µg/mL or 4 µg/mL further emphasize the diminishing efficacy of vancomycin, reinforcing the role of daptomycin as an advantageous alternative, but the critical transition point is at 2 µg/mL. This understanding helps guide clinicians in making informed decisions about antibiotic therapy for serious MRSA infections