Simple Warfarin Dosing Algorithm Study

Warfarin reduces the risk of thromboembolism, but requires regular blood monitoring to keep the international normalized ration (INR) within a narrow therapeutic range to achieve maximum benefits. A low proportion of time spent within the therapeutic INR range, (TTR) is associated with reduced warfarin efficacy and potentially harmful results. To optimize TTR, international guidelines recommend the use of systematic evidence-based dosing methods (anticoagulation clinic, computerized systems, manual algorithm and patient self-management). A survey in the Hamilton area revealed that half of family physicians manage warfarin dosing without assistance from an evidence-based method. The simple manual dosing algorithm is a simple tool that helped increase the TTR at the Hamilton General Hospital's anticoagulant clinic to an excellent 73% among patients with target INR range 2-3. We will test whether the simple dosing algorithm can help to improve warfarin dosing of family physicians who are not assisted by evidence-based methods. We will randomize family practices to either use the simple dosing algorithm or to manage warfarin dosing as usual, to test whether the simple dosing algorithm achieves a superior TTR.

Inclusion criteria

• Family practices that:

• currently do not employ an evidence-based dosing method (anticoagulant clinic, computer system, manual algorithm or patient self-testing),
• manage warfarin maintenance dosing in at least 10 patients with target INR 2-3, and
• have at least one family physician providing written informed consent.
• Patients who:

• are on long-term warfarin treatment (> 6 weeks before study entry and expected to continue for at least 6 more months) with target INR 2-3, for whom warfarin is managed by a participating family physician,
• patient provides written informed consent.

Exclusion criteria

• Family practices that:

• are planning to start employing an evidence-based method for warfarin dosing within the next year,
• are not expected to enroll at least 10 patients on long-term warfarin treatment with target INR 2-3.
• Patients:

• with < 3 months warfarin management prior to the baseline observation,
• patients on warfarin with a target INR other than 2-3, and
• patients for whom warfarin is managed by a physician who is not participating in the trial.