Which first-line TB drug is associated with orange-red discoloration of bodily fluids but is otherwise harmless?

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

Answer: (C)

Rifampin is the drug that can turn bodily fluids orange-red, a harmless dye effect you’ll often see in patients taking this first-line TB medication. The pigment in rifampin colors urine, sweat, tears, and even contact lenses, but this color change doesn’t indicate toxicity; it’s simply the drug’s dye being excreted. Mechanistically, rifampin works by inhibiting bacterial DNA-dependent RNA polymerase, effectively stopping RNA synthesis and killing Mycobacterium tuberculosis. That’s why it’s a staple in the RIPE regimen. Besides the harmless discoloration, rifampin can cause hepatotoxicity and flu-like symptoms, and it’s a potent inducer of hepatic enzymes, which can reduce the effectiveness of other drugs (such as oral contraceptives). The other first-line drugs have different side-effect profiles—ethambutol can cause optic neuritis, isoniazid can cause neuropathy and hepatotoxicity, and pyrazinamide can cause hyperuricemia—so the orange-red fluid discoloration specifically points to rifampin.