RSS Feeds
Managing Excessive Warfarin Anticoagulation
Warfarin is very effective in preventing thromboembolic events, but it is probably one of the most dangerous drugs that is used on a long-term basis. Warfarin reduces the risk for stroke in atrial fibrillation by approximately 85%, but almost one half of eligible patients do not receive such therapy (1, 2). Apparently, many clinicians do not use warfarin for fear of bleeding complications.
In this issue, Hylek and colleagues (3) provide valuable new information that should improve the ability to manage excessive warfarin anticoagulation and reduce risk for bleeding. Their review of 633 patients with excessive elevation of the international normalized ratio (INR) found that lower maintenance doses of warfarin, advanced age, decompensated heart failure, and active cancer were associated with a gradual decrease in high INRs. Since Rosendaal and associates (4) developed a method of calculating the time spent in different INR ranges, several studies have reported a strong correlation between bleeding complications and time spent at high INRs. As the INR increases above 5.0, the risk for major hemorrhage increases exponentially in many patients (5-7). This increase in risk starts at INRs above 3.0 in older patients with a previous cerebrovascular event (8, 9). The strong association between INR and risk for bleeding led to the recommendation that “time in target INR range” be used as a surrogate end point for rates of warfarin complications (10).
Several issues should be considered before applying Hylek and colleagues' findings. First, the study was retrospective, and the researchers therefore did not confirm the index INR with repeated measurements, did not account for factors that may yield erroneous INRs, and incompletely evaluated the role of interacting medications. Clearly, the findings of a retrospective study …
