What is a major safety concern with linezolid, and what drug interaction must be monitored?

• A. Nephrotoxicity; interaction with NSAIDs
• B. Thrombocytopenia; interaction with serotonergic agents
• C. Hepatotoxicity; interaction with statins
• D. QT prolongation; interaction with antiarrhythmics

Answer: (B)

Linezolid has two important safety considerations, and the most clinically relevant one is its effect on the bone marrow, which can lead to thrombocytopenia. This means platelets can drop during treatment, increasing the risk of bleeding, and the risk rises with longer courses of therapy or in patients with preexisting hematologic issues. Because of this, clinicians monitor blood counts regularly during linezolid treatment, especially if it’s going to extend beyond a week or two.

Another critical point is linezolid’s reversible monoamine oxidase inhibition, which can raise serotonin levels in the body. When combined with other serotonergic medications—such as SSRIs, SNRIs, TCAs, MAO inhibitors, or certain pain medications and cough suppressants that affect serotonin—there’s a risk of serotonin syndrome. This can present with agitation or restlessness, confusion, rapid heart rate, high blood pressure, dilated pupils, loss of muscle coordination, muscle rigidity, tremor, sweating, shivering, and diarrhea. Because of this, it’s essential to review a patient’s meds and monitor for signs of serotonin syndrome, adjusting therapy as needed.

Other potential interactions mentioned in some references, like nephrotoxicity with NSAIDs or QT prolongation with antiarrhythmics, are not the primary safety concerns for linezolid.