Which drug is associated with optic neuritis as a potential adverse effect?

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

Answer: (A)

Optic neuritis is a well-known adverse effect of ethambutol. This drug can affect the optic nerve, leading to reduced visual acuity and color vision abnormalities, most notably difficulties with red-green discrimination. The risk increases with higher daily doses and longer duration of therapy, but it can be reversible if the medication is stopped early and vision is monitored.

Because of this potential toxicity, baseline and periodic ophthalmologic assessment are advised, and any new visual symptoms should prompt evaluation and possible dose adjustment or discontinuation. In contrast, the other anti-tubercular drugs have different main toxicities: rifampin is commonly linked to hepatotoxicity and harmless orange discoloration of body fluids; isoniazid to neuropathy (often due to vitamin B6 deficiency) and hepatotoxicity; pyrazinamide to hyperuricemia and hepatotoxicity.