What is the effect of rifampin on cytochrome P450 enzymes and what are the clinical implications?

• A. Potent inhibitor of CYP enzymes; reduces levels of many drugs
• B. Moderate inhibitor of CYP enzymes; increases levels of some drugs
• C. Potent inducer of CYP enzymes; reduces levels of many drugs; orange-red bodily fluids
• D. No significant effect on CYP enzymes

Answer: (C)

Rifampin acts as a powerful inducer of hepatic cytochrome P450 enzymes, especially CYP3A4. By activating these enzymes, it increases their production and activity, which speeds up the metabolism and clearance of many drugs that are substrates of these enzymes. Clinically, this means lower drug levels in the blood and a higher risk that other therapies will be less effective unless doses are adjusted or alternative treatments are used. An easy-to-notice clue is that rifampin can cause orange-red discoloration of bodily fluids—urine, sweat, tears, and even contact lenses. This induction effect takes days to weeks to develop and can persist for a while after stopping rifampin, so monitoring for drug interactions is important during and after its use.