Warfarin could reduce risk for pulmonary embolisms, deep-vein thrombosis
When 39-year-old David Bloom, an NBC news correspondent in Iraq, suddenly died of a pulmonary embolism this spring, the life-threatening condition made headlines. Pulmonary embolisms are most often related to deep-vein thrombosis (DVT), essentially a blood clot in a leg vein. Sometimes, all or part of the clot will break away from the vein wall and lodge in an artery in the lungs. This is a pulmonary embolism. While traveling with the Army in Iraq, Bloom reported sleeping with his knees propped up. Staying immobile like this can cause circulation to slow. Sluggish blood flow is one cause of clots. DVT can also be caused by blood that has a greater-than-normal tendency to clot.
Although in Bloom's case the condition was not detected in time, pulmonary embolisms and DVT are treatable. Patients are often initially prescribed heparin and then switched over to warfarin for 3 to 12 months. Both of these drugs are anticoagulants; they help thin the blood by preventing it from clotting. But a little clotting is necessary; to prevent uncontrollable bleeding we need our blood to clot. Frequent blood tests help doctors determine the amount of medication necessary for a safe balance of clotting and thinning.
The balance becomes tricky once the typical treatment of heparin and warfarin is complete. If anticoagulation therapy is stopped, the risk of recurring DVT returns. But previous studies have shown extended use of warfarin at full-dose leads to a risk of serious hemorrhaging.
To help solve this Catch-22, researchers started a trial of long-term, low-intensity warfarin treatment in comparison to treatment with a placebo. Over 500 patients were enrolled in the study; roughly half receiving low-intensity warfarin and the other half receiving a placebo. Data from this study, published in the New England Journal of Medicine, show low-intensity warfarin treatment is superior to a placebo. The risk of recurring DVT was 64% less in those patients who received warfarin, compared to those who received the placebo. Even participants with an inherited tendency to form blood clots experienced comparable reductions in risk. The number of major bleeding episodes was similar between the two treatment groups. These results were so positive that the study was halted early.
Preliminary results from a different study, however, somewhat contradict these findings. Data from this study show treatment with low-intensity warfarin is less effective than treatment with standard-intensity warfarin for long-term prevention of recurring DVT.
To reconcile the differences between these two studies, a three-way comparison of warfarin at full-dose, low-intensity, and no treatment is needed. Until then, talk to your doctor about which treatment, if any, is right for you.
July 2003 Update