Which TB drug has monoamine oxidase-inhibitor-like properties and can interact with SSRIs?

• A. Linezolid
• B. Isoniazid
• C. Ethambutol
• D. Pyrazinamide

Answer: (A)

The main concept here is that one TB drug acts like a monoamine oxidase inhibitor and can interact with SSRIs, raising the risk of serotonin-related toxicity. Linezolid fits this because, beyond its antibacterial action, it reversibly inhibits monoamine oxidase A and B in human tissues. This inhibition slows the breakdown of serotonin, so when linezolid is used with serotonergic drugs such as SSRIs, serotonin levels can surge and provoke serotonin syndrome.

In TB care, linezolid is increasingly used for multidrug-resistant or extensively drug-resistant TB, which is why understanding this interaction matters. Clinically, you’d watch for signs like agitation, confusion, tremor, hyperreflexia, fever, and autonomic instability. If linezolid is needed alongside an SSRI, options include adjusting or temporarily stopping the SSRI, choosing an antidepressant with a lower risk of serotonergic interaction, or close multidisciplinary management to mitigate risk.

The other TB drugs listed do not have MAOI-like activity, so their interactions with SSRIs aren’t driven by monoamine oxidase inhibition. They have their own safety concerns (for example, isoniazid can cause neuropathy from vitamin B6 depletion, ethambutol can cause optic neuritis, and pyrazinamide can cause hyperuricemia and hepatotoxicity), which are separate issues from MAO inhibition.