A 24-year-old man on an XDR-TB regimen containing linezolid for six months presents with progressive numbness of the feet and blurring of vision. Fundus examination shows optic pallor. Full blood count was normal until recently. The best next step is:

• A Continue linezolid and add pyridoxine alone
• B Stop linezolid immediately and reassess the regimen ✓
• C Switch linezolid to amikacin
• D Reassure, since these symptoms resolve spontaneously without stopping the drug

Explanation

Linezolid causes cumulative mitochondrial toxicity with prolonged use: peripheral neuropathy, optic neuritis that can progress to irreversible blindness, and myelosuppression (especially thrombocytopenia). Neuropathy and optic neuritis are indications to stop the drug, since they may not reverse fully. Pyridoxine may reduce risk but does not permit continuation once optic involvement appears. Amikacin would substitute one neurotoxic agent for another.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.