tPA and the Anticoagulants Heparin and Warfarin

Anticoagulants are used for the treatment of deep venous thromboses (DVTs). Anticoagulants "thin" the blood, impairing coagulation and making it more difficult for blood clots to form. Anticoagulants also help to dissolve existing blood clots. Depending on the cause of DVT, anticoagulants may be used both as short-term treatment and long-term prevention.

Of all the anticoagulants, heparin is often the first choice for DVT treatment. Heparin works quickly, but must be administered intravenously. Because heparin's effect on the anticoagulation factors in the blood can vary widely, heparin treatment requires careful monitoring. Traditionally, heparin treatment has required hospitalization.

Researchers have succeeded in developing a new formulation of heparin called low molecular weight heparin, or LMWH. Low molecular weight heparin has a more predictable effect on anticoagulation and can be injected subcutaneously every twelve hours. These advances make it less necessary for low molecular weight heparin treatment to require hospitalization. Some patients can even self-administer LMWH at home.

While heparin treatment works quickly, warfarin is an oral anticoagulant that takes days to begin to thin the blood. Warfarin, therefore, must be taken for four to five days before treatment reaches its maximum effectiveness. This slow action makes warfarin less appropriate than heparin for emergency DVT treatment.

Warfarin, however, is one of the anticoagulants that can be taken over long periods of time. After initial DVT treatment with heparin, oral warfarin may be prescribed for up to six months. After two or more cases of DVT, life-long warfarin treatment may be recommended to prevent further blood clots.

Warfarin causes birth defects, so it cannot be used while pregnant. Pregnant women who require anticoagulants are prescribed heparin (LMWH) instead.

Thrombolytic medication is sometimes combined with anticoagulants for DVT treatment. Thrombolytic drugs use tissue plasminogen activator (tPA), or urokinase, to dissolve blood clots. tPA treatment is delivered directly into the bloodstream through an IV.

Because tPA is such a strong treatment, it can only be used under certain circumstances. For example, a patient must not have any existing bleeding disorders since a side effect of tPA is a much greater risk of excessive bleeding than with either heparin or warfarin. In addition, a definite diagnosis of DVT must be made by a venography before tPA treatment will be considered, and the DVT must usually have been present for less than three days. The limitations of tPA treatment make thrombolytic medications less favorable than heparin or warfarin, so tPA is usually only used as a DVT treatment in specific circumstances.

 

 

Tovey, C. & Wyatt, S. (2003). Diagnosis, investigation, and management of deep vein thrombosis. British Medical Journal, 326, 1180-1185.

 

National Library of Medicine. (updated 2004). Venous insufficiency. Retrieved January 16, 2004, from
www.nlm.nih.gov/medlineplus/ency/article/000203.htm.

 

Beers, M. H. & Berkow, R. (ed). Venous thrombosis [electronic version]. The Merck Manual of Diagnosis and Therapy, 17th Edition. Merck Research Laboratories, NJ, 1999.
www.merck.com/mrkshared/mmanual/section16/chapter212/
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