Rifampicin, rifapentine and, to a lesser extent, rifabutin are among the most powerful enzyme inducers in clinical use, acting on CYP3A4, several other CYP enzymes, glucuronidation and P-glycoprotein.
The effect builds over about a week and takes up to two weeks to wear off after stopping, so a drug dose increased during treatment can become toxic afterwards. Common casualties include hormonal contraception, warfarin, direct oral anticoagulants, many antiretrovirals, calcineurin inhibitors, azoles, methadone and some antiepileptics.
Before starting any rifamycin, review the full medicine list, including over-the-counter and traditional remedies.
- Review every co-medication before starting a rifamycin
- Advise a non-hormonal or unaffected contraceptive method
- Expect induction to persist for up to two weeks after stopping
- Re-check doses of interacting drugs once the rifamycin ends
Why it matters
Rifamycin interactions cause treatment failure on the way in and toxicity on the way out.
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