Warfarin Drug Side Effects

Warfarin (Coumadin) is an anticoagulant medication used for the prevention and treatment of blood clots. It is currently the only anticoagulant that can be taken by mouth rather than by injection in the U.S, making it a commonly used medication. As with any anticoagulant, bleeding is the primary side effect. Patients taking warfarin must have blood tests done regularly to assure that the dose is high enough to prevent blood clots but low enough to lessen the risk of bleeding. The blood test monitors the INR---for most patients, the goal is to maintain the INR between 2.0 and 3.0. If kept within this range, warfarin can generally be taken safely. Aside from bleeding, other side effects are rare.

Bleeding

Warfarin does not actually cause bleeding per se but increases its likelihood if an area already exists that is prone to bleeding such as a sore or a weakened blood vessel. Bleeding unleashed by warfarin can occur at any body site and range in severity anywhere from very minor to life-threatening. The gastrointestinal tract is the most common site for bleeding, whereas bleeding into the brain (i.e., intracranial hemorrhage) is the most serious. Major bleeding, generally defined as bleeding requiring hospitalization or a blood transfusion, is rare if the INR does not exceed 3.0. According to the 2008 Clinical Practice Guidelines on Antithrombotic Therapy, the incidence of major bleeding in patients not taking warfarin is about 1 percent per year, compared to about 1.3 percent per year in those taking warfarin whose INRs are maintained within the targeted range of 2.0 to 3.0. Higher INRs proportionately increase the risk of bleeding. Other factors may also increase the risk of bleeding and include advanced age, concurrent use of certain other drugs that interfere with platelet activity or increase the INR, kidney failure, past episodes of gastrointestinal bleeding, recent surgery or trauma, and cancer. Patients taking warfarin should notify all of their health-care providers, including other physians, pharmacists, and dentists, to lessen the risk of bleeding from medical procedures and drug interactions.

Skin Necrosis

Less than 0.1 percent of patients taking warfarin develop a serious skin condition called warfarin-induced skin necrosis. This condition is more prevalent in women, particularly those who are middle-aged, usually occurs within 10 days of starting warfarin, and initially produces a painful rash in areas of high fat content such as the breasts, buttocks, abdomen, and thighs. This rash rapidly progresses to dark, bleeding, seeping areas that may require surgery.

Purple Toe Syndrome

Purple toe syndrome is an extremely rare side effect of warfarin in which the toes actually have a purple or mottled discoloration. This effect usually occurs after 1 to 3 months or more of warfarin therapy and is thought to be due to microembolization of cholesterol. Though usually reversible, warfarin should be discontinued if it develops.