A 45-year-old woman is being treated for suspected TB and has noticed that her urine has turned a deep red colour. Which medication is most likely responsible for this adverse drug reaction?

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

Answer: (A)

Rifampicin can color body fluids orange‑red, including urine, tears, and sweat. This staining is a harmless, drug-related pigment excreted in the urine and is a well-known side effect of rifampicin. It can look alarming but does not indicate harm or toxicity; it’s simply a characteristic feature of the medication.

The other TB drugs have different adverse effect profiles: isoniazid is mainly associated with liver toxicity and neuropathy; pyrazinamide with hepatotoxicity and urate elevation; ethambutol with optic neuritis and possible visual changes. So the deep red urine point most strongly to rifampicin as the cause. If seen, it’s usually reassuring, though liver function should still be monitored and any other symptoms assessed.