Which first-line TB drug is associated with optic neuritis and color vision changes?

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

Answer: (A)

Optic neuritis with color vision changes is a classic adverse effect of ethambutol, a first-line anti-TB drug. Ethambutol can damage the optic nerves in a dose- and duration-dependent way, especially in people with reduced kidney function. Patients may notice decreased visual acuity and difficulty distinguishing colors, most notably along the red–green axis. This vision change can appear weeks to months after starting therapy and is often reversible if the drug is stopped promptly, though sometimes it can be permanent if exposure is prolonged or severe.

In practice, clinicians monitor vision when ethambutol is used and adjust or discontinue the drug if visual symptoms develop. Other first-line TB meds like isoniazid, rifampin, or pyrazinamide do not typically cause optic neuritis or color vision defects; they have other toxicity profiles (for example, neuropathy with isoniazid due to B6 deficiency, hepatotoxicity and metabolic effects with rifampin and pyrazinamide). The drug responsible for the described eye effects is ethambutol.