Vitamin K antagonist (oral anticoagulant)
Warfarin with antibiotics: interactions and safety
Antibiotic courses are common, short-term and often combined with chronic medications such as Warfarin (Warfarin). Most antibiotics do not interfere meaningfully with Warfarin at 1mg, 2mg, 2.5mg, 3mg, 4mg, 5mg, but a few classes do, and a small number of combinations are best avoided.
Common antibiotic interactions
Macrolides (clarithromycin, erythromycin) and certain antifungals can inhibit hepatic metabolism (CYP3A4) and raise plasma levels of many medications including some Vitamin K antagonist (oral anticoagulant) agents. Rifampicin has the opposite effect, accelerating metabolism. Most penicillins, cephalosporins, fluoroquinolones and tetracyclines have no clinically meaningful interaction with Warfarin at 1mg, 2mg, 2.5mg, 3mg, 4mg, 5mg.
Practical guidance
According to the prescribing information for Warfarin, an antibiotic course should be reviewed by the prescriber or pharmacist for known interactions before Warfarin is co-administered. Adjusted 1mg, 2mg, 2.5mg, 3mg, 4mg, 5mg dosing or temporary substitution is sometimes preferred for the duration of the antibiotic course.
Frequently asked questions
Can I take Warfarin during an antibiotic course? ▾
For most common antibiotics, yes. A few classes — notably macrolides and azole antifungals — alter how Warfarin is metabolised and may need a temporary 1mg, 2mg, 2.5mg, 3mg, 4mg, 5mg adjustment. The prescribing pharmacist should review any new antibiotic against the existing Warfarin regimen.
Will antibiotics make Warfarin stop working? ▾
Most antibiotics do not affect Warfarin efficacy. Rifampicin and a few others can lower Warfarin levels and reduce effect; in those cases the prescriber may adjust the dose during and shortly after the antibiotic course.
Products containing Warfarin
More on Warfarin
- With alcoholWarfarin and alcohol — is it safe to drink?
- With foodShould Warfarin be taken with food?
- Side effectsWarfarin side effects: common, rare and warning signs
- Dosage guideWarfarin dosage guide: how much to take and when
- OnsetHow fast does Warfarin start working?
- DurationHow long does Warfarin last?
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