Abstract and Introduction
Systematic management models such as anticoagulation clinics have emerged in order to optimize warfarin effectiveness and to minimize related complications. Most of these models are structured so that patients come to a clinic for in-person testing and evaluation, thus making this model of care difficult to access and time consuming for many patients. The emergence of portable instruments for measuring anticoagulant effect in capillary whole blood made it possible for patients receiving warfarin to self-monitor the effect of their anticoagulant therapy. Self-monitoring empowers patients, offers the advantage of more frequent monitoring, and increases patient convenience by allowing testing at home and avoiding the need for frequent laboratory and clinic visits. Self-monitoring can entail patient self-testing (PST) and/or patient self-management (PSM). Several studies have evaluated and shown the benefit of both PST and PSM models of care when compared with either routine medical care or anticoagulation clinic management of anticoagulation therapy. Self-monitoring (PSM and/or PST) of anticoagulation results in lower thromboembolic events, lower mortality, and no increase in major bleeding when compared with standard care. Despite favorable results and enhanced patient convenience, the adoption of self-monitoring into clinical practice in the United States has been limited, especially in higher risk, disadvantaged populations. Although the emergence of a multitude of novel oral anticoagulants will permit clinicians to better individualize anticoagulant therapy options by choosing the optimum regimen based on individual patient characteristics, it is also expected that traditional agents will continue to play a role in a significant subset of patients. For those patients treated with traditional anticoagulants such as warfarin, future models of care will entail patient-centered management such as PST and PSM. The incorporation of technology (i.e., Web-based expert systems) is expected to further improve the outcomes realized by PST and PSM. Further studies are needed to explore factors that influence the adoption of self-monitoring in the United States and to evaluate the feasibility and implementation in real-life clinical settings.
Warfarin is the most commonly prescribed oral anticoagulant therapy in the United States and is effective for prevention and treatment of venous thromboembolism (VTE) and thromboembolism in the setting of prosthetic heart valves, atrial fibrillation, and myocardial infarction. With the increase in the aging U.S. population, the number of patients treated with warfarin has continued to increase. In 2004 alone, the number of dispensed outpatient prescriptions for warfarin was nearly 31 million. Approximately 4 million outpatients in the United States and almost 7 million worldwide are receiving long-term oral anticoagulant therapy, primarily warfarin or other coumarin derivatives.[2,3] Warfarin is an effective anticoagulant when dosed appropriately; however, its use requires systematic monitoring and close patient follow-up because of its narrow therapeutic index and several clinical and genetic factors that influence its dose response. The aim of treatment is to prolong clotting time to a level to prevent thrombosis but not above a level to cause bleeding. Monitoring is performed by using either venous or capillary blood samples, and results are reported as the international normalized ratio (INR). The goal INR, which is determined based on the clinical indication for warfarin, is 2.5 (range 2.0–3.0) for most indications, but a higher goal of 3.0 (range 2.5–3.5) is indicated in patients with mechanical heart valves guided by the type and position of the valve.
For decades, warfarin has been the cornerstone of anticoagulation, with few alternatives and no other oral options. However, as clinical use of warfarin is complex, clinicians and patients have longed for an oral alternative with similar effectiveness and safety, fewer monitoring requirements, and a cleaner drug-interaction profile. Novel oral anticoagulants have been developed to address many of the shortcomings of warfarin therapy, and several of these agents have been recently approved or are in clinical development. These include the direct thrombin inhibitor dabigatran and the direct factor Xa inhibitors rivaroxaban, edoxaban, and apixaban.[4–6] Rivaroxaban and dabigatran are approved in Europe and Canada for prevention of VTE in patients undergoing hip or knee replacement surgery,[7,8] and dabigatran was approved in October 2010 in the United States and Canada for prevention of stroke in patients with atrial fibrillation, and it is now also approved in Europe for this indication. Rivaroxaban was approved for prevention of VTE in patients undergoing hip or knee replacement surgery in the United States in July 2011. These novel agents have the potential to make anticoagulant treatment and prophylaxis more convenient, as they are available for oral administration in fixed doses, and they have short half-lives, rapid onset of action, and a more limited list of drug interactions. Since they produce a predictable anticoagulant response, there is no requirement for routine monitoring.[4–8]
Despite their potential advantages, there is cautious optimism as to the degree of acceptance into clinical practice of these novel agents. Although they deliver on the promise of convenience, many questions remain surrounding their safe and appropriate incorporation into clinical practice. As stated above, their administration requires no routine coagulation monitoring; however, there are certain clinical scenarios in which knowledge of the degree of anticoagulant effect is needed for effective and safe patient care (e.g., prior to an invasive procedure, occurrence of a hemorrhagic or thrombotic event, or assessment of compliance), but currently there is no single standard test to evaluate their effect in these scenarios. Their acquisition cost is high, approximately $7–9/day, which can prohibit access for many patients, especially the uninsured and underserved. It is also important to note that no reversal agent has been determined for any of the new agents, and little data are available on the use of blood products or dialysis for the management of bleeding. Limited data are available on their use in patients with renal dysfunction, obese patients, the pediatric population, and pregnant women, and guidelines are lacking for transitioning between these agents and other oral and parenteral anticoagulants, their use in neuraxial anesthesia, and their use in populations in which anticoagulants are routinely used, such as patients with stroke or acute coronary syndromes, or those requiring cardioversion or ablation therapy.
It is thus expected that, until these issues are resolved and until we accumulate a more mature real-life safety database with these new agents, warfarin will remain a major part of the oral anticoagulant drug armamentarium. Over the years, various models of management have evolved with the intent of high-quality oral anticoagulation delivery. In this review, we give an overview of these models with a special emphasis on the role and place in the U.S. practice of patient self-monitoring.
Pharmacotherapy. 2011;31(12):1161-1174. © 2011 Pharmacotherapy Publications