Which MRSA-active antibiotic requires CBC monitoring for thrombocytopenia and has potential SSRI interactions?

• A. Vancomycin — trough monitoring; nephrotoxicity
• B. Linezolid — CBC monitoring for thrombocytopenia; SSRI interactions
• C. Daptomycin — myopathy; not for pneumonia due to surfactant
• D. Ceftaroline — MRSA activity; assess beta-lactam allergy

Answer: (B)

Linezolid stands out because it covers MRSA and has two distinctive safety concerns: it can cause bone marrow suppression, leading to thrombocytopenia that requires CBC monitoring, and it has MAOI-like activity that can interact with SSRIs to produce serotonin syndrome. Prolonged use increases the risk of platelet count drop, so observing CBCs during therapy helps catch this early. The serotonergic interaction means patients on SSRIs or other serotonergic drugs are at risk if linezolid is used concurrently, so coordination or alternative therapies are often needed.

Vancomycin also treats MRSA but is checked by trough levels to monitor for nephrotoxicity, not for thrombocytopenia or SSRI interactions. Daptomycin can cause myopathy and isn’t appropriate for pneumonia due to surfactant interference. Ceftaroline has MRSA activity as a beta-lactam but does not carry the specific CBC or serotonergic interaction concerns associated with linezolid.