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Warfarin Therapy: Tips and Tools for Better Control

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Warfarin Therapy: Tips and Tools for Better Control David A. Garcia, MD; Michael J. Schwartz, MD Anticoagulation Clinic, Warfarin therapy: University of New Mexico Health Sciences Center, Albuquerque (Dr. Garcia); Tips and tools for better control Health Services at Columbia University, New York, NY (Dr. Schwartz, retired) Monitoring patients on warfarin therapy is challenging. [email protected] Th e tools highlighted here—from online forums and Dr. Garcia reported that he receives Web-based dosing calculators to patient education research support from, and serves as a consultant to, Bristol-Myers materials and self-monitors—can help. Squibb and serves as a consultant to Boehringer Ingelheim; Dr. Schwartz reported that he has no potential confl ict of interest relevant to this article. pproximately 4 million Americans are receiving long- PRACTICE term oral anticoagulation therapy to reduce the risk of RECOMMENDATIONS Aprimary and secondary thromboembolism.1,2 And, as › INR testing by an anti- the population ages, the number of patients on lifelong thera- coagulation management py with warfarin—the only oral anticoagulant available in the service or private clinician United States until dabigatran was approved by the US Food can be reduced to intervals of and Drug Administration late last year3—is expected to grow.4 as long as 4 weeks, but should Such patients present a challenge for family physicians. be more frequent when dos- Warfarin is notorious for having both a narrow therapeutic ing adjustments occur. B index and numerous drug and dietary interactions.5,6 To safe- › Weekly patient self-testing guard patients on warfarin therapy, frequent, and diligent, is associated with comparable monitoring is required. clinical outcomes to high- Engaging patients as participants in their own care can quality clinic-based antico- help you decrease the hazards. With that in mind, this article agulation management. A features warfarin treatment tips and tools for both physicians › Patients who self-test (and and patients, along with a review of some basic safeguards. report their results) weekly should test more frequently when a change in medication (including herbal remedies Warfarin therapy: Keeping it safe and dietary supplements) or Warfarin, a vitamin K antagonist, is used to prevent systemic diet or an illness occurs. C embolism in patients with prosthetic heart valves, atrial fi brilla- tion, or inherited/acquired thrombophilic disorders; as an ad- Strength of recommendation (SOR) junct in the prophylaxis of systemic embolism after myocardial A Good-quality patient-oriented evidence infarction (MI); and to reduce the risk of recurrent MI, as well 4,7 B Inconsistent or limited-quality as venous thromboembolism. Because there is a small but patient-oriented evidence defi nite risk (1%-2% per year)8 of severe bleeding associated C Consensus, usual practice, opinion, disease-oriented with warfarin, however, therapy should be initiated only when evidence, case series the potential benefi ts clearly outweigh the risks. A major contraindication for warfarin therapy is early preg- nancy. Th e anticoagulant is a teratogen, causing deformations of the face (depressed nasal bridge) and bones (stippled epiphy- ses), neonatal seizures, and spontaneous abortion. If a woman in the fi rst trimester of pregnancy requires anticoagulation, low- molecular-weight heparin should be substituted instead.9 70 THE JOURNAL OF FAMILY PRACTICE | FEBRUARY 2011 | VOL 60, NO 2 A recent study confi rmed that self-testing is feasible for most warfarin- treated patients and that weekly home monitoring is as safe and effective as high-quality clinic-based testing. In fact, warfarin is not recommended in the indicate a need for a lower dose.11 A number of second or third trimesters either, as the use of Web-based dosing calculators (TABLE) can help vitamin K antagonists increases the risk of mis- clinicians estimate the therapeutic dose in pa- carriages, structural defects, and other adverse tients who are new to warfarin. outcomes. Nor is warfarin recommended for Th yroid activity also aff ects warfarin dos- women who are planning to become pregnant. ing requirements.12 Hypothyroidism makes Warfarin is also contraindicated in pa- people less responsive to warfarin,13 while tients for whom the risk of major bleed- hyperthyroidism boosts the anticoagulant ing outweighs the benefi ts. Risk factors for eff ect.14 Several mechanisms have been pro- warfarin-associated bleeding include renal in- posed for this eff ect, including changes in the suffi ciency and concomitant antiplatelet ther- rate of breakdown of clotting factors and in apy, and physicians can use published clinical the metabolism of warfarin.15,16 prediction rules to estimate bleeding risk.10 ❚ Frequency of monitoring. Regardless of the initiation dose, INR values of outpatients Dosing considerations should be monitored at least 2 to 3 times a When you start a patient on warfarin therapy, it week for the fi rst 7 to 10 days of therapy, or un- is important to ensure that therapeutic concen- til a stable value is achieved. (In an inpatient trations are achieved in a timely manner—and setting, INR monitoring is usually performed that the risk of supra- and subtherapeutic inter- daily until the therapeutic range has been national normalized ratio (INR) values—≥4.0 maintained for ≥2 days.) Th e target INR level and <2.0, respectively—is minimized.6 varies from case to case depending on the clin- IMAGE © JOE GORMAN Factors to consider in determining the ical indicators, but tends to be between 2 and starting dose include patient-specifi c measures 3 for most patients and between 2.5 and 3.5 for such as age, height, and weight; concomitant those with mechanical heart valves.17 medications; and comorbidities. Increasing After stabilization, testing can be reduced age, female sex, and a low body mass index all to intervals of as long as 4 weeks, although JFPONLINE.COM VOL 60, NO 2 | FEBRUARY 2011 | THE JOURNAL OF FAMILY PRACTICE 71 evidence suggests that more frequent testing who are independent and self-supporting leads to greater time-in-therapeutic range are, in principle, capable of self-management (TTR).18,19 When dosing adjustments are re- of oral anticoagulation, regardless of educa- quired, the cycle of more frequent monitor- tion or social status.23,,24 Th e only intellectual ing should be repeated until a stable dose requirement is that the patient (or caregiver) response can again be achieved. grasp the concept of anticoagulant therapy and understand the potential risks. (For more help in determining whether your patient is Benefi ts of patient involvement eligible for self-management, see “Self-moni- Patients on warfarin may be managed in one or toring—for which patients?” on page 74.) more of the following 3 methods: (1) with usual Th e patient must also be willing to ac- care, provided by the patient’s personal physi- tively participate in his or her own care and cian; (2) by anticoagulation management ser- have suffi cient manual dexterity and visual vices (AMSs), specialized programs overseen acuity. No previous experience in self-testing by physicians, pharmacists, and/or nurses; or or monitoring is necessary.7 (3) by self-testing/self-management, with the help of point-of-care devices that allow pa- tients to monitor their own INR levels and ad- INR monitors for patients just their anticoagulation dose, within certain and physicians Medicare covers limits, in consultation with a clinician.4 Since the late 1980s, point-of-care devices the cost of INR Many nonrandomized retrospective stu- that measure INR values have made it pos- monitors and dies have reported better outcomes in patients sible for an increasing number of patients to testing materials whose anticoagulant therapy is managed by an monitor the anticoagulant eff ects of warfarin for patients on AMS vs management by a primary care physi- without repeat visits to a health care facil- anticoagulation cian or specialist alone.7 Compared with usual ity. Of the 4 million US residents on warfa- therapy care, AMS programs have been shown to greatly rin, approximately 60,000 (1.6%) engage in associated with improve patients’ TTR, thereby reducing hem- self-testing, according to the International mechanical heart orrhage or thrombosis as a consequence of ex- Self-Monitoring Association of Oral Antico- valves, chronic cessive or subtherapeutic anticoagulation.4,20,21 agulated Patients (www.ismaap.org). atrial fi brillation, Self-testing/self-management—which One reason may be the cost. Portable or VTE. depends on adequate patient training—has monitors are available for approximately similar benefi ts: Self-care facilitates more $2495, according to Alere Inc., a health man- frequent monitoring and empowers patients, agement company—a price that may include and may be a major factor in patient compli- supplies and training. Th e expense may not ance.4 Individuals using their own portable be covered by private insurers. However, INR monitors and managing their own care in 2008, Medicare began covering the cost have been found to have improved TTRs and of INR monitors (and the testing materials a lower frequency of major hemorrhage or required for their use) for seniors receiv- thrombosis compared with patients receiv- ing anticoagulation therapy associated with ing usual care.7,18 Th e recent THINRS trial mechanical heart valves, chronic atrial fi - randomized 2922 patients to perform weekly brillation, or venous thromboembolism.25 self-testing or receive monthly clinic-based Portable monitoring devices include the testing at an institution with a system for following: providing anticoagulant care. Th e study con- ❚ CoaguChek (http://www.coaguchek. fi rmed that patient self-testing is feasible for com). Th e CoaguChek brand, now in its third most warfarin-treated individuals and that g eneration, features both a monitor (Coagu- weekly home monitoring is as safe and eff ec- Chek XS) for patient use and a system (Coa- tive as high-quality clinic-based testing.22 guChek XS Plus) for health care professionals.
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