A 45-year-old man on standard anti-tuberculosis therapy (2HRZE/4HR) complains of difficulty distinguishing red and green colors after 3 months of treatment. Which drug is most likely responsible for this adverse effect?
- A Ethambutol ✓
- B Isoniazid
- C Rifampicin
- D Pyrazinamide
Correct answer: A. Ethambutol
Explanation
Ethambutol causes dose-dependent optic neuritis, which characteristically presents as red-green color blindness and decreased visual acuity. The mechanism involves chelation of copper, leading to mitochondrial dysfunction and axonal degeneration in the optic nerve. Rifampicin causes orange discoloration of body fluids and hepatotoxicity, not visual disturbances. Isoniazid causes peripheral neuropathy and hepatotoxicity. Pyrazinamide causes hyperuricemia and hepatotoxicity.
Reference: Katzung Basic & Clinical Pharmacology, 15th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.