What is the principal adverse effect of long-term isoniazid therapy?

Correct answer: C. Hepatitis (hepatotoxicity)

• A. Ototoxicity, both vestibular and cochlear, belongs to STREPTOMYCIN.
• B. Nephrotoxicity is not characteristic of isoniazid. Among the antituberculars, the aminoglycoside streptomycin is the nephrotoxic agent.
• C. CORRECT. HEPATOTOXICITY is the major concern with isoniazid. Transient asymptomatic transaminase elevation occurs in 10 to 20% of patients, and clinically significant hepatitis in roughly 0.5 to 1%, with risk rising sharply with age and with concurrent alcohol use. Liver function is monitored throughout therapy, and the drug is stopped if transaminases climb.
• D. Optic neuritis with loss of red-green colour discrimination is the signature toxicity of ETHAMBUTOL.

Note: The RIPE regimen and its toxicities: Rifampin causes orange discolouration of body fluids and is a potent CYP450 INDUCER that will reduce the effect of many co-prescribed drugs. Isoniazid causes hepatitis and peripheral neuropathy, the latter prevented by co-prescribing pyridoxine (B6). Pyrazinamide causes hyperuricaemia and gout. Ethambutol causes optic neuritis.