warfarin and dabigatran

MajorAvoid this combination where possible.

Mechanism

Pharmacodynamic interaction. Warfarin inhibits vitamin K-dependent coagulation factors (II, VII, IX, X), while dabigatran is a direct thrombin inhibitor. Co-administration produces additive anticoagulant effects, markedly increasing bleeding risk.

What it means clinically

Patients are at high risk of serious and potentially fatal haemorrhage, including intracranial and gastrointestinal bleeding. This combination should generally be avoided, except in specific switching protocols under close medical supervision.

What to do

Avoid co-prescription. When switching from warfarin to dabigatran, stop warfarin and wait until the International Normalised Ratio (INR) is below 2.0 before starting dabigatran (for most indications). When switching from dabigatran to warfarin, start warfarin while continuing dabigatran for 2–3 days, then stop dabigatran and adjust warfarin dose based on INR. However, this is not routine practice and should follow local guidance.

Evidence

Well-established from pharmacology, clinical trials and post-marketing surveillance; contraindicated in most formularies.

The two drugs

warfarinVitamin K antagonistRead the monograph dabigatranDirect oral anticoagulantRead the monograph

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Other interactions involving warfarin or dabigatran

Educational reference for students and clinicians in training. It does not replace professional judgement, local protocols or current prescribing information.