Bismuth subcitrate, metronidazole, and tetracycline and Warfarin interaction
Bismuth subcitrate, metronidazole, and tetracycline and Warfarin: both prescribing labels describe an interaction that usually calls for monitoring, a dose change, or spacing the doses.
Usually manageable with monitoring or a dose change. Tell your pharmacist you take both.
What the FDA labels say
From the Bismuth subcitrate, metronidazole, and tetracycline (Bismuth Subcitrate Potassium, Metronidazole and Tetracycline Hydrochloride) label · effective 2026-04-13
Closely monitor prothrombin time, International Normalized Ratio (INR), or other suitable anticoagulation tests if bismuth subcitrate potassium, metronidazole and tetracycline hydrochloride is administered concomitantly with warfarin.
Prothrombin time, International Normalized Ratio (INR), or other suitable anticoagulation tests should be closely monitored if bismuth subcitrate potassium, metronidazole and tetracycline hydrochloride is administered concomitantly with warfarin.
Metronidazole has been reported to potentiate the anticoagulant effect of warfarin, and other oral coumarin anticoagulants, resulting in a prolongation of prothrombin time.
Anticoagulants: Potentiation of the anticoagulant effect; Prothrombin time, International Normalized Ratio (INR), or other suitable anticoagulation tests should be closely monitored.
Anticoagulants Bismuth subcitrate potassium, metronidazole and tetracycline hydrochloride may alter the anticoagulant effects of warfarin and other oral coumarin anticoagulants.
From the Warfarin (Warfarin Sodium) label · effective 2026-06-24
Table 2: Examples of CYP450 Interactions with Warfarin Enzyme Inhibitors Inducers CYP2C9 amiodarone, capecitabine, cotrimoxazole, etravirine, fluconazole, fluvastatin, fluvoxamine, metronidazole, miconazole, oxandrolone, sulfinpyrazone, tigecycline, voriconazole, zafirlukast aprepitant, bosentan, carbamazepine, phenobarbital, rifampin CYP1A2 acyclovir, allopurinol,…
Inhibitors of CYP2C9, 1A2, and/or 3A4 have the potential to increase the effect (increase INR) of warfarin by increasing the exposure of warfarin.
Taking more than these two? Interactions stack. Check your whole list at once; it stays in your browser.
Open in the checkerNot medical advice. Interaction Checker quotes FDA label text and NIH fact sheets. Whether an interaction matters for you depends on doses, timing, kidney and liver function, and other conditions. Confirm with a pharmacist or prescriber.