A patient on anti-TB therapy (RHEZ regimen) develops orange discoloration of urine and tears. Which drug is responsible, and why is this finding clinically important to counsel the patient about?

• A Ethambutol; it indicates early ocular toxicity
• B Rifampicin; it is a harmless side effect but can permanently stain soft contact lenses ✓
• C Isoniazid; it indicates hepatotoxic metabolite accumulation
• D Pyrazinamide; it indicates hyperuricemia causing tubular secretion of colored metabolites

Explanation

Rifampicin (rifampin) is an orange-red compound that imparts its color to bodily secretions including urine, tears, saliva, sweat, sputum, and cerebrospinal fluid. This is a harmless and expected pharmacological property related to the drug's chromophore. Patient counseling is essential so they do not become alarmed and discontinue therapy. The major practical clinical implication is that soft contact lenses can be permanently stained orange-red; patients should be advised to wear glasses or use disposable lenses during therapy. Rifampicin is also a potent CYP inducer, meaning enzyme induction effects on co-administered drugs are clinically far more significant than the cosmetic discoloration.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.