Warfarin Therapy: Evolving Strategies in Anticoagulation

JON D. HORTON, PHARM.D., and BRUCE M. BUSHWICK, M.D.

York Hospital

York, Pennsylvania

Warfarin is the oral anticoagulant most frequently used to control and prevent thromboembolic disorders. Prescribing the dose that both avoids hemorrhagic complications and achieves sufficient suppression of thrombosis requires a thorough understanding of the drug’s unique pharmacology. Warfarin has a complex dose-response relationship that makes safe and effective use a challenge. For most indications, the dose is adjusted to maintain the patient’s International Normalized Ratio (INR) at 2 to 3. Because of the delay in factor II (prothrombin) suppression, heparin is administered concurrently for four to five days to prevent thrombus propagation. Loading doses of warfarin are not warranted and may result in bleeding complications. Interactions with other drugs must be considered, and therapy in elderly patients requires careful management. Current dosing recommendations are reviewed, and practical guidelines for the optimal use of warfarin are provided.

Warfarin (Coumadin) is the most frequently prescribed oral anticoagulant, the fourth most prescribed cardiovascular agent and the overall eleventh most prescribed drug in the United States,¹ with annual sales of approximately $500 million.²Nonetheless, in 1995 the Agency for Healthcare Policy and Research (AHCPR)³reported that warfarin is greatly underutilized for stroke prevention. The AHCPR noted that physicians are reluctant to prescribe warfarin, in part because they are not familiar with techniques for administering the drug safely and fear that the drug will cause bleeding. Patients treated with warfarin do require close monitoring to avoid bleeding, but it has been shown that the drug prevents 20 strokes for every bleeding episode that it causes.³  Read Full Article