What adverse effect is most commonly associated with ethambutol requiring routine visual testing?

• A. Peripheral neuropathy.
• B. Hepatotoxicity.
• C. Nephrotoxicity.
• D. Optic neuritis with decreased visual acuity and color vision.

Answer: (D)

Ethambutol has a distinctive toxicity: its major adverse effect is optic neuritis, which presents as reduced visual acuity and impaired color vision (especially red-green). This toxicity is dose- and duration-related, and early detection is key because stopping the drug can often reverse the changes before permanent damage occurs. That’s why routine visual testing is recommended—baseline eye examination followed by regular monitoring of vision and color perception (often with simple color vision tests).

Other adverse effects listed—peripheral neuropathy, hepatotoxicity, and nephrotoxicity—are not the hallmark toxicity that requires eye monitoring for ethambutol, though they can occur with various TB drugs. The emphasis here is on the optic nerve toxicity that necessitates regular eye checks.