Dabigatran × Warfarin

Warfarin blocks vitamin K-dependent clotting factor synthesis; dabigatran is a direct thrombin inhibitor. The two mechanisms are additive with bleeding risk.

Gum bleeding, epistaxis, bruising without trauma, blood in urine or stool, menorrhagia. Severe cases include gastrointestinal or intracranial haemorrhage, gross haematuria with renal colic, spontaneous retroperitoneal haematomas. Symptoms may appear within days of co-prescription.

The combination is not prescribed. Switching from warfarin to dabigatran: stop warfarin, wait for INR below 2.0, then start dabigatran. Reverse switch: start warfarin 3 days before stopping dabigatran if creatinine clearance is over 50 mL/min, 2 days if 30–50 mL/min, 1 day if below 30 mL/min.