Critical
Apixaban × Warfarin
Direct oral anticoagulants (factor Xa inhibitors)×Vitamin K antagonist anticoagulants
Mechanism
Warfarin blocks vitamin K-dependent clotting factor synthesis (II, VII, IX, X); apixaban directly inhibits factor Xa. The two different mechanisms add up.
Symptoms
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.
Management
The combination is not prescribed. Switching from warfarin to apixaban: stop warfarin, wait for INR below 2.0, then start apixaban. Switching from apixaban to warfarin: overlap with INR monitoring, stop apixaban once INR exceeds 2.0.