Self-management of warfarin by the patient is an attractive strategy particularly if it improves anticoagulation control and can be done safely under minimal physician supervision. We conducted a randomized study at a single Canadian center to compare self-management (SM) with conventional physician-managed (PM) anticoagulation. Patients 18 years or older were eligible if they had received warfarin for at least 1 month prior and had planned anticoagulation for at least 1 year to a target international normalized ratio (INR) of 2.0 to 3.0 or 2.5 to 3.5. Exclusion criteria were known hypercoaguable disorder, mental incompetence, language barrier or inability to attend training sessions. Patients randomized to the SM group received extensive training to self-test their INR using a point-of-care device (ProTime) and adjust their warfarin doses using an individualized dosing nomogram. Patients randomized to the PM arm received usual care from their general practitioner. The primary outcome was a comparison of the proportion of INR values and time in target range between the groups. One hundred and forty patients were randomized (70 per group) and followed for 8 months. Seventeen patients did not complete the SM arm, 8 due to inability to self-manage, and 3 patients did not complete the PM arm. Based on an intention-to-treat analysis, there was no difference in proportion of INR values in range (SM 64.8% vs PM 58.7%, p=0.46) and time in target range (SM 71.8% vs PM 63.2%, p=0.28). Per-protocol analysis showed that SM patients spent significantly less time below the therapeutic range (12.0% vs 27.3%, p=0.025). Patients in the SM group performed nearly twice as many INR determinations than physicians (mean 27.9 vs 16.5 per patient over 8 months, p<0.0001). There were 3 major complications of thrombosis or major bleeding, all in the PM arm. Patients managing their own therapy made 40/1615 (2.5%) incorrect warfarin dosage adjustment decisions but none resulted in adverse consequences. All patients who completed the SM arm indicated a preference to continue managing their own therapy. Our study shows that self-management of warfarin is feasible and safe in a carefully selected, well-trained population.

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