Doctors commonly give blood thinners (anticoagulants) to patients who are at risk for the formation of blood clots that can result from many medical conditions. Warfarin, a pill that is taken by mouth, is commonly used for its anticoagulant effect. Warfarin is both effective and convenient to take, but it requires a few days to achieve adequate anticoagulation after the first dose and its effect on blood clotting lasts for 3 to 5 days after patients have stopped taking it. When a patient taking warfarin must undergo surgery, doctors have to stop warfarin treatment about 5 days before the procedure because anticoagulation can cause excessive bleeding, especially when tissues are cut. On the other hand, when the patient is not protected by anticoagulation, the risk for a dangerous blood clot increases. Doctors often handle this dilemma by stopping warfarin treatment several days before surgery and substituting a drug from a class of anticoagulants known as low-molecular-weight heparin. One member of this class is enoxaparin, a medication that must be given by injection, either once or twice daily. Enoxaparin treatment also must be stopped shortly before surgery, but because its effect does not last as long as that of warfarin, it can be stopped a shorter time before surgery. Common practice is to give the last dose of twice-daily enoxaparin the evening before surgery. Once surgery is finished, enoxaparin treatment is restarted until warfarin therapy is resumed adequately. Using enoxaparin this way is known as “bridging” therapy.