Patient Care Hematology & Oncology - October 2007 - (Page 8)

I Bridge anticoagulation Drugs mentioned in this article Argatroban (Novastan) Bivalirudin (Angiomax) Dalteparin (Fragmin) Desirudin (Iprivask) Enoxaparin (Lovenox) Fondaparinux (Arixtra) Heparin Insulin Lepirudin (Refludan) Tinzaparin (Innohep) Warfarin (Coumadin) • Start unfractionated heparin (UFH) in its place • Discontinue UFH on the day of the procedure • Resume UFH immediately postprocedure • Resume OAC postprocedure • Discontinue UFH when OAC reaches therapeutic levels. Notable problems with this approach include • Lack of consensus on the appropriate perioperative management of the patient who requires chronic OAC • The requirement of hospitalization and the cumbersome, time-consuming, and costly aspects of the protocol. Though UFH remains the standard of care for periprocedural bridge anticoagulation therapy, lowmolecular-weight heparin (LMWH) shows great promise to replace it. The problems with UFH in bridge therapy are largely resolved with LMWH. Bridging with LMWH is simple, requires little or no monitoring, and can be performed in an ambulatory care setting. Studies using LMWH in bridge therapy are promising, but randomized controlled trials are lacking. The clinician is left with little evidence to guide therapy in the periprocedural period. We propose to review the evidence for bridge anticoagulation therapy with UFH and LMWH, including the following related issues: • Indications—to bridge or not to bridge • Options—UFH versus LMWH • Protocols for UFH and LMWH bridge therapy • LMWH-specific issues in bridge therapy • Cost analysis associated with bridge therapy. Warfarin and warfarin therapy An understanding of warfarin’s mechanism of action and pharmacokinetics is required to design a rational strategy for bridge anticoagulation therapy. Warfarin exerts its anticoagulant effects by inhibiting the coagulation factors dependent on vitamin K (factors II, VII, IX, and X), as shown in Figure 1 (page 9). The half-life of warfarin is based on the half-life of the coagulation factors it affects. Accordingly, it takes 4 to 5 days after warfarin institution for therapeutic levels to be achieved, and its effects persist 4 to 5 days after its discontinuation. Measurement of prothrombin time (PT) prolongation is expressed by the international normalized ratio (INR), in which the subject’s PT is the numerator and a standardized normal PT is the denominator. Determination of the optimal warfarin dosage is hindered by its narrow therapeutic index and variable dose-response relationship from patient to patient. For these reasons, blood levels need to be monitored routinely to assure effective and safe dosing in both the initiation and the maintenance periods. For most of the indications for chronic OAC, a target INR between 2 and 3 is effective in preventing the formation of a clot while safe enough to prevent major bleeding.1,2 The perioperative period poses special risks for the patient requiring OAC. The risk of VTE must be weighed against the risk of serious bleeding. Not all conditions for which OAC is indicated carry the same risk for VTE. In addition, not all surgical procedures carry the same risk of bleeding in anticoagulated patients. To bridge or not to bridge Not all surgical procedures require interruption of OAC. The menu of options for the periprocedural management of anticoagulation includes • No interruption of OAC, keeping INR in therapeutic range • Discontinuation of warfarin therapy approximate- 8 PATIENT CARE HEMATOLOGY & ONCOLOGY www.patientcareonline.com http://www.patientcareonline.com

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Patient Care - Hematology & Oncology - October 2007 Research Digest Contents Information for Authors Medicine in the News Strategies for Bridge Anticoagulation Therapy How to Integrate the New Cervical Cancer Guidelines into Practice Dermatology Case Challenge Clinical Clips Classified Advertising

Patient Care Hematology & Oncology - October 2007

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