Determinants of bleeding with warfarin

The risk of bleeding is highest during the first 3 months of warfarin therapy. While the risk decreases after 3 months, it persists above baseline for the duration of therapy.

The major determinants of bleeding during warfarin therapy are:

• the international normalised ratio (INR)
• the duration of therapy
• concurrent drug therapy
• other patient factors (see Patient-associated factors that increase bleeding risk with anticoagulant therapy).

Both the target INR and the achieved INR influence the risk of bleeding—the risk of bleeding increases significantly when the target INR is more than 3 and the achieved INR is more than 5. For patients with a high INR, in addition to reviewing the warfarin dose, seek precipitating factor(s) and modify them if possible. For patients with a persistently high or labile INR, reassess the suitability of ongoing warfarin therapy and consider an alternative anticoagulant.

Risk factors for major bleeding includeTran, 2013:

• a major bleed within the preceding 4 weeks
• surgery within the preceding 2 weeks
• a platelet count of less than 50 × 10⁹/L
• liver disease
• concurrent antiplatelet therapy.

Concurrent therapy with antiplatelet drugs (eg aspirin, clopidogrel, prasugrel, ticagrelor) increases the risk of bleeding during warfarin therapy but does not increase the INR. NSAIDs increase the risk of gastrointestinal bleeding during warfarin therapy.

For the management of patients who are bleeding, see Bleeding and overanticoagulation in patients taking warfarin therapeutically.