American Board of Internal Medicine (ABIM) Certification Practice Exam

In patients with MRSA bacteremia, when is vancomycin not recommended?

1. If the MIC is less than 2 µg/mL

2. If the MIC is between 1 and 3 µg/mL

3. If the MIC to vancomycin is greater than 2 µg/mL

4. If the MIC is exactly 2 µg/mL

The correct answer is: If the MIC to vancomycin is greater than 2 µg/mL

In patients with MRSA (Methicillin-resistant Staphylococcus aureus) bacteremia, the susceptibility of the organism to vancomycin is critical for determining the appropriate treatment. Vancomycin is generally the go-to antibiotic for treating MRSA infections, but its effectiveness is influenced by the minimum inhibitory concentration (MIC). When interpreting the MIC values, it is essential to remember that an MIC greater than 2 µg/mL indicates reduced susceptibility to vancomycin. Specifically, if the MIC is greater than 2 µg/mL, this suggests that higher doses of vancomycin may be necessary to achieve therapeutic levels, and there may be a significant risk that the drug will not effectively control the infection. This is particularly concerning in serious infections such as bacteremia, where appropriate coverage is essential to avoid treatment failure. The importance of this MIC threshold reflects the challenges associated with treating MRSA, especially in severe infections where high vancomycin levels are needed to penetrate tissues effectively and eliminate the pathogen. Therefore, when the MIC is greater than 2 µg/mL, vancomycin is not recommended as the primary treatment option due to concerns about resistance and potential treatment failure. In such cases, alternative agents, such