Blood clots that form in the legs are known medically as deep venous thrombosis (DVT). Risk factors for developing a DVT include immobility (prolonged travel or hospitalization, for example), major surgery (especially hip or knee replacements), cancer, advanced age, pregnancy and estrogen therapy. DVTs warrant prompt medical treatment because they can lead to a pumonary emboli (PE), which can be rapidly fatal. This happens when the blood clot breaks loose from the leg vein and travels through the blood vessels to the lungs, where it becomes lodged. If symptoms of a DVT are experienced, such as pain, swelling, or warmth in the leg, seek medical care so that a diagnosis can be made. If a DVT is found or suspected, anticoagulants--drugs that prevent blood from clotting--are the primary therapy.
LMWH and Warfarin
Most patients with a DVT can be treated at home. The patient or a caregiver can be taught how to administer a low molecular weight heparin (LMWH), such as dalteparin (Fragmin®), enoxaparin (Lovenox®), or tinzaparin (Innohep®) by subcutaneous injection once or twice daily. Warfarin (Coumadin®), an anticoagulant taken by mouth, is started at the same time as the LMWH. Because it takes several days for warfarin to start working, the LMWH is used for at least the first 5 days of therapy and then may be discontinued in most patients. Patients with cancer should continue only the LMWH for at least 3 months, according to the 8th edition of the American College of Chest Physicians Evidence-Based Clinical Practice Guidelines published in "Chest" in 2008. Other patients can expect to remain on warfarin alone for at least 3 months.
Fondaparinux and Warfarin
Fondaparinux (Arixtra®) is an alternative to a LMWH in the regimen described above. Fondaparinux works slightly differently than the LMWHs but is also given by subcutaneous injection, once daily. It also is overlapped for at least 5 days with warfarin.
Heparin and Warfarin
Patients unable or unwilling to learn to self-inject with a LMWH or fondaparinux require treatment in the hospital with heparin for the first 5 days. Like the other regimens, warfarin is overlapped with the heparin initially, after which warfarin alone is used for at least 3 months. Heparin is generally given by intravenous infusion and requires monitoring with blood tests. While the actual drug costs are lower with this approach, the overall cost of treatment is much higher due to the need for hospitalization.
On the Horizon
Though not yet on the U.S. market, several new anticoagulants may gain FDA approval fairly soon and may simplify treating DVTs. Currently, the only available oral anticoagulant is warfarin, which is slow to start working, requires careful blood monitoring and interacts with many drugs and foods. Oral anticoagulants in advanced stages of clinical trials that do not possess these limitations include dabigatran, rivaroxaban, and apixaban. If and when these drugs are approved for the treatment of DVT, it may be possible to avoid injectable therapy entirely.
References
- "Chest"; Antithrombotic Therapy for Venous Thromboembolic Disease; Clive Kearon, MB, PhD, Susan R. Kahn, MD, Giancarlo Agnelli, MD, et al. June 2008
- "America's Pharmacist"; Oral, Direct Factor Xa Inhibitors and Thromboembolic Disorders; Karissa Kim, Bradley Hein, Patricia Wigle. February 2009
- "Pharmacotherapy: A Pathophysiologic Approach"; DiPiro JT, Talbert RL, Yee, GC, et al, editors, 2005. Chapter 19 "Venous Thromboembolism", Haines ST, Zeolla M, Witt DM.
- "AHFS Drug Information"; McEvoy GK, editor; 2009.
