Quality of warfarin management

I read with interest the excellent article on warfarin management in Canada in the June issue of Canadian Family Physician.¹ I was particularly pleased to see Liu and colleagues make the important point that “conservative” management of warfarin (underdosing in an effort to avoid hemorrhage) is a potentially dangerous practice and leads to a greater risk of stroke than hemorrhage,¹ which in general is more catastrophic (20% mortality, 59% disability).² This can be clearly seen in the classic graph by Hylek and Singer,² where the odds of ischemic stroke and intracranial hemorrhage are plotted against the patient’s international normalized ratio (INR).

Although this situation is sometimes deliberate on the part of the physician (worried about a major bleed), it is often due to poor adherence on the part of the patient. Elderly minds become forgetful, as we all know. In this situation, more frequent testing might be helpful (eg, every 2 weeks) and the use of a reminder mechanism (eg, an INR log app or a telephone call from a family member or caregiver) might also be helpful. The good news with poor adherence and warfarin is that its long half-life (72 hours) gives the patient a “second chance.” This is not the case with the direct oral anticoagulants, which have a shorter half-life (8 to 12 hours). For this reason, using a direct oral anticoagulant can put the forgetful patient at risk, as there is no routine blood test (like an INR or drug level) to tip us off.

Second, although Liu et al found that only 52.7% of INRs were within range in cases where atrial fibrillation, deep vein thrombosis, and pulmonary embolism were the indications for treatment, I am pleased that they recognized the potential for considerable improvement (eg, Sweden’s registry with 80.3% of INRs within therapeutic range).¹ The disparity between Canada and Sweden demonstrates the great need for Canada to “pull up its socks.” The same technologies (point-of-care testing, computer decision support software, trained operators, patient self-management programs) are available to us as well. And these types of services do make a difference (eg, time in therapeutic range of 74% with New Zealand’s Community Pharmacy Anticoagulation Management Service program³; time in therapeutic range of > 80% with Germany’s self-management program⁴). And they do need wide adoption in our country. The cost of missing the opportunity to emulate Sweden’s performance is huge in terms of all-cause mortality (60% reduction),⁵ stroke and systemic embolism (49% reduction),⁵ and major hemorrhage (59% reduction),⁵ and commensurate cost reductions to our health care system.

Thank you, Liu and colleagues, for the excellent article, and let’s work together in Canada to improve warfarin management and achieve some “Viking” results!