MAJOR — Use With Caution
🔴 AVOID — FDA-documented interaction. Clarithromycin increases warfarin levels via CYP3A4 inhibition. INR monitoring essential. Consider azithromycin as a safer macrolide alternative.
Evidence level: STRONG
Clarithromycin (Biaxin) can significantly increase warfarin blood-thinning effect. This antibiotic blocks the enzymes that clear warfarin from your body, raising your risk of dangerous bleeding.
Clarithromycin is a strong CYP3A4 inhibitor and moderate CYP1A2 inhibitor. Increases warfarin R-enantiomer levels. FDA warfarin label lists macrolide antibiotics as increasing anticoagulant effect.
If prescribed clarithromycin while on warfarin, get your INR checked within a few days. Ask your doctor if azithromycin could be used instead, as it has less interaction with warfarin.
Monitor closely. Many antibiotics amplify anticoagulant effects by disrupting gut flora that produce vitamin K. Warfarin levels may spike during antibiotic courses. If on warfarin, request more frequent INR monitoring. Take each at their normal prescribed times.
Higher risk for: elderly patients, those with liver disease, history of GI bleeding, concurrent use of multiple blood thinners, recent surgery, vitamin K intake changes, alcohol use, or low body weight.
Easy bruising, blood in urine or stool, nosebleeds, excessive bleeding from minor injuries
Ask about azithromycin as an alternative (weaker enzyme inhibition). Request INR monitoring during and after the antibiotic course.
This medication combination requires careful medical oversight. Your doctor or anticoagulation clinic can adjust doses or select alternatives with fewer bleeding risks. Frequent INR monitoring is essential.
Clarithromycin (Biaxin) can significantly increase warfarin blood-thinning effect. This antibiotic blocks the enzymes that clear warfarin from your body, raising your risk of dangerous bleeding.
Monitor closely. Many antibiotics amplify anticoagulant effects by disrupting gut flora that produce vitamin K. Warfarin levels may spike during antibiotic courses. If on warfarin, request more frequent INR monitoring. Take each at their normal prescribed times.
Easy bruising, blood in urine or stool, nosebleeds, excessive bleeding from minor injuries
This medication combination requires careful medical oversight. Your doctor or anticoagulation clinic can adjust doses or select alternatives with fewer bleeding risks. Frequent INR monitoring is essential.
Ask about azithromycin as an alternative (weaker enzyme inhibition). Request INR monitoring during and after the antibiotic course.
Or browse the full interaction database (121,000+ pairs).