Which of the following medications are NOT recommended for MRSA infections?

• A. Clindamycin/Lincomycin
• B. Bactrim
• C. Clarithromycin
• D. Vancomycin

Answer: (C)

MRSA carries resistance mechanisms that make macrolide antibiotics unreliable for treating these infections. The resistance typically comes from methylation of the 23S rRNA target by erm genes, which blocks macrolide binding and can produce inducible resistance. Because of this, clarithromycin (a macrolide) is not a reliable choice for MRSA. Other options like Bactrim can be effective for many CA-MRSA skin infections, and vancomycin remains a mainstay for invasive MRSA. Clindamycin can be used in selected MRSA cases when the strain lacks inducible clindamycin resistance (negative D-test). The key idea is that MRSA commonly exhibits macrolide resistance, making clarithromycin inappropriate, while other agents have reliable activity against MRSA in appropriate contexts.