Losartan and Rifampin: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Rifampin
Losartan
How we grade severity & evidence
Severity levels
- Contraindicated: These should generally not be used together.
- Major: Potentially serious — often needs a change or close monitoring.
- Moderate: Can be significant — usually manageable with monitoring.
- Minor: Usually limited clinical impact.
Evidence grades
- Established: Well documented — supported by controlled studies or strong clinical data.
- Probable: Good supporting evidence, though not definitively proven.
- Suspected: Some evidence suggests this interaction, but it is not well established.
- Possible: Limited or conflicting evidence; the interaction may occur.
- Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.
Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.
What happens
Reduced losartan exposure and reduced losartan active metabolite exposure
Interaction Deep Dive
Exert caution when rifAMPin is coadministered with drugs metabolized with cytochrome P450, such as losartan1. Coadministration of rifAMPin and losartan may reduce losartan and its active metabolite exposure 231. Losartan is an angiotensin II subtype 1 (AT1) receptor antagonist that is metabolized to E3174, which is a more potent inhibitor at AT1 receptors than losartan. E3174 is primarily responsible for the antihypertensive activity of losartan. Losartan is metabolized by cytochrome P450 2C9 and 3A4 enzymes to E3174. RifAMPin significantly induced the metabolism of losartan and E3174, resulting in a decrease in the area under the concentration-time curve (AUC) and half-life of both compounds 4.
Why it happens (mechanism)
Induction of CYP2C9-mediated metabolism of losartan
Literature reports
1 report — tap to read
a) Ten healthy volunteers received losartan 50 mg daily for seven days, losartan and erythromycin 500 mg four times daily for seven days, and losartan and rifAMPin 300 mg twice daily for seven days. Each period was separated by a 6-day washout phase. Coadministration of erythromycin with losartan did not significantly affect the AUC, half-life, or oral clearance of losartan and had no effect on the AUC or half-life of E3174. By contrast, rifAMPin decreased the AUC of losartan and E3174 by 35% (349 ng/hr/mL vs. 225 ng/hr/mL) and 40% (1336 ng/hr/mL vs. 792 ng/hr/mL), respectively. The half-life of both losartan (2 hours vs. 0.9 hours) and E3174 (5.1 hours vs. 2.5 hours) was also decreased by approximately 50% in the presence of rifAMPin. Erythromycin is a moderate inhibitor of cytochrome P450 3A4 (CYP3A4) enzymes, and rifAMPin is the most potent inducer of the cytochrome P450 system. Losartan is metabolized by CYP2C9 and CYP3A4 to E3174, and because of the lack of a significant effect caused by erythromycin, it appears that CYP2C9 plays a more prominent role than CYP3A4 in the metabolism of losartan to E3174 4.
Common questions
Can I take Losartan and Rifampin together?
Reduced losartan exposure and reduced losartan active metabolite exposure Always confirm with your pharmacist or prescriber before making any change.
How serious is the Losartan and Rifampin interaction?
It is rated major. Potentially serious — often needs a change or close monitoring.
How quickly could this interaction happen?
The documented onset is "delayed". Effects tend to build up gradually over days to weeks.
How strong is the evidence for this interaction?
The evidence is graded "probable". Good supporting evidence, though not definitively proven.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
Questions for your pharmacist
- Does my dose of Losartan or Rifampin need adjusting while I take them together?
- What symptoms should prompt me to call you or my prescriber right away?
- Does the timing of my doses matter for this combination?
- Is there a safer alternative to one of these medications for me?
References (4)
- Product Information: RIFATER(R) oral tablets, rifampin, isoniazid, pyrazinamide oral tablets. sanofi-aventis US LLC (per FDA), Bridgewater, NJ, 2023. DailyMed
- Product Information: RIFADIN(R) IV intravenous injection, rifampin intravenous injection. sanofi-aventis US LLC (per FDA), Bridgewater, NJ, 2023. DailyMed
- Product Information: RIFADIN(R) oral capsules, rifampin oral capsules. sanofi-aventis US LLC (per FDA), Bridgewater, NJ, 2023. DailyMed
- Williamson KM, Patterson HP, McQueen RH, et al: Effects of erythromycin or rifampin on losartan pharmacokinetics in healthy volunteers. Clin Pharmacol Ther 1998; 63:316-323.
Keep reading about Rifampin
Keep reading about Losartan
These medications also interact with supplements
Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:
major · moderate · minor — check everything you take with our drug–supplement interaction checker.
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