THE FEASIBILITY OF PATIENT SELF-MANAGEMENT OF WARFARIN THERAPY IN THE CANADIAN PRIMARY CARE SETTING

BACKGROUND Oral anticoagulants have seen large popularity due to their ease of administration and proven benefit in a variety of conditions. In an examination of patients in Manitoba, 7.2% of the elderly population was being treated with warfarin therapy, a proportion which is likely similar across Canada. For atrial fibrillation, the dose of warfarin is titrated using INR as a guide to a target of 2.0-3.0, a therapeutic range with significant evidence of decreased thromboembolic events while minimizing the risk of major hemorrhage2. Other indications for anticoagulation therapy include presence of a mechanical heart valves, a history of deep vein thromboses or pulmonary embolism(s), or other pro-thrombotic conditions.

Ever since the introduction of warfarin into routine clinical practice, maintenance of a therapeutic INR in patients has proven to be a difficult task, with patients only spending an average of 57-66% of the time within therapeutic range. As the majority of these patients in Canada are treated by primary care providers, busy family physicians must keep a watchful eye on INR values, which are constantly changing due to diets with varying amounts of Vitamin K, not to mention the effects of interacting drugs and other confounders.

In an attempt to find alternative strategies for anticoagulation treatment several randomized control trials have been undertaken in the last two decades examining the idea of "Patient Self-Management" (PSM) of anticoagulation. In a scheme similar to diabetics monitoring their blood glucose values and altering insulin dosages, patients in these trials have been taught to self-test their INR values using home electronic devices and then adjust their warfarin doses accordingly. Data has been published showing improved control in therapeutic range and decreased complication rates of thromboembolic events and major hemorrhages. There was no significant decrease in mortality in the above studies, although most were not powered to detect this as sample sizes were small (49-737 participants). In 2006 a systematic review and meta-analysis of 14 randomized control trials (RCT's) was published involving 3049 participants comparing "Patient Self-Monitoring" (ie. no adjustment of dose) and/or PSM to standard management Data from seven PSM studies was included which demonstrated a significant decrease in thromboembolic events, a non-significant decrease in major hemorrhagic events, and a significant decrease in mortality. Furthermore, it was shown that patients were more satisfied with PSM strategies. These data are reflected in the American College of Chest Physicians guideline entitled Pharmacology and Management of Vitamin K Antagonists, "In patients who are suitably selected and trained, PST [patient self-testing] or PSM is an effective alternative treatment model. We suggest that such therapeutic management be implemented where suitable".

In an attempt to compare the success of anticoagulation control in all arenas, Walraven and associates examined 67 studies involving 50 208 patients with 57 154 patient-years from anticoagulation clinics, clinical trials, and community practises. Study investigators examined many variables which may have influenced differences in therapeutic control and concluded that study setting was the greatest predictor. They quoted the following rates of anticoagulation success: PSM 72%, RCT's 66%, anticoagulation clinics 66%, and community primary care clinics 57%. It was also shown that PSM was associated with a significant improvement in anticoagulation control.

In considering the practise of family medicine in Canada, two facts regarding anticoagulation control are apparent: (a) family physicians shoulder the majority of the treatment responsibility; and (b) control is likely not optimal. PSM in RCT's have shown to improve therapeutic control in patients when compared to "usual care"5,7 and also to care from anticoagulation clinics in tertiary care hospitals. This improved control has shown to be associated with improved clinically relevant endpoints. Thus, it would be logical to suggest that implementing PSM strategies in Canadian primary care settings would have the greatest return. There are several problems with this logic though. Firstly, RCT's all involved extensive training sessions with nurse clinicians or specialized physicians at tertiary care centres to educate participants in the fundamentals of warfarin therapy and the adjustment regimes. These resources are simply not available for family physicians. Secondly, "point of care" electronic INR testing devices were provided to all patients, which would cost an average patient approximately $1000 with the added cost of testing strips.