A 32-year-old man from rural Maharashtra presents with a 3-month history of productive cough, fever, and weight loss. Chest X-ray shows bilateral apical infiltrates. Sputum smear microscopy is positive for acid-fast bacilli. He is started on standard first-line antitubercular therapy (RIPE: rifampicin, isoniazid, pyrazinamide, ethambutol). After 2 weeks of therapy, he develops acute onset red discoloration of urine and tears. His liver function tests remain normal. What is the most likely cause of these symptoms?

Explanation

## Rifampicin-Induced Orange-Red Discoloration ### Clinical Presentation The patient's acute onset of red/orange discoloration of urine, tears, and other body fluids is a classic and benign side effect of **rifampicin**, not a sign of organ toxicity. ### Mechanism **Key Point:** Rifampicin is a lipophilic drug that undergoes hepatic metabolism and is excreted in bile and urine, imparting an orange-red color to body secretions. **High-Yield:** This discoloration affects: - Urine (orange-red) - Tears (orange-red — may stain contact lenses) - Saliva - Sweat - Breast milk ### Why This Is NOT Pathological **Clinical Pearl:** This is a **cosmetic side effect**, not a sign of toxicity. It occurs in 100% of patients on rifampicin and requires reassurance, not drug discontinuation. ### Differential Considerations | Feature | Rifampicin Discoloration | Hepatotoxicity | Nephrotoxicity | |---------|--------------------------|----------------|----------------| | Onset | Days 1–2 | Weeks 2–8 | Weeks 3–6 | | LFTs | Normal | Elevated AST/ALT | Normal | | Urine color | Orange-red | Normal | Normal or dark | | Reversibility | Immediate on cessation | Slow, may be permanent | Variable | | Clinical consequence | None | Serious | Serious | ### Management **Tip:** Counsel the patient that: - This is expected and harmless - Discoloration will resolve within days of stopping the drug - Contact lens wearers should use glasses during treatment - No dose adjustment or drug change is needed ### Antitubercular Drug Toxicity Profile **Key Point:** Common serious toxicities to monitor: - **Isoniazid**: Peripheral neuropathy (prevent with pyridoxine), hepatotoxicity, drug-induced lupus - **Rifampicin**: Hepatotoxicity (rare), drug interactions (induces CYP450) - **Pyrazinamide**: Hyperuricemia, hepatotoxicity, arthralgias - **Ethambutol**: Optic neuritis (red-green color blindness), peripheral neuropathy [cite:KD Tripathi 8e Ch 49]