Medicines can help prevent repeated episodes of pulmonary embolism by preventing new blood clots from forming or preventing existing clots from getting larger.

Medication Choices

Anticoagulants are prescribed when pulmonary embolism is diagnosed or strongly suspected. Normally, when an injury that causes bleeding occurs, the body sends out signals that cause the blood to clot at the wound. The clot naturally breaks down as the wound heals. A person who is prone to abnormal clotting has an imbalance between clot formation and clot breakdown. Anticoagulants prevent the production of certain proteins that are necessary for blood to clot. Although anticoagulants can prevent new clots from forming and prevent existing clots from getting larger, they do not break up or dissolve existing blood clots.

Heparin and warfarin are the two main types of anticoagulants used to treat pulmonary embolism.

Heparin

Heparin is an anticoagulant given by injection. It immediately affects the clotting system in your body. Oral anticoagulant medicine (warfarin) takes longer to start working.

• Initial treatment with a low-molecular-weight heparin (LMWH) usually is preferred because it can be given as an injection once or twice per day, and it may be given at home, allowing you to leave the hospital earlier.⁹ Blood tests are not usually needed to monitor LMWH's clotting effect.
• Unfractionated heparin is another form that can be used. It is given in the hospital. Unfractionated heparin is usually given continuously through your vein (intravenously, or IV), but can also be given as an injection under the skin. Frequent blood tests (usually every 6 hours) are required to monitor the clotting effects of this medicine.¹

Early studies show that LMWH may be equally as effective as unfractionated heparin in most people with pulmonary embolism.¹² However, it is still unclear whether LMWH is a good choice in treating a large pulmonary embolism. Some doctors may still prefer to use unfractionated heparin in these severe cases.

Both forms of heparin can cause severe bleeding in some people. The risk that either type will cause bleeding appears to be about the same.⁹ However, if bleeding occurs, unfractionated heparin can be stopped quickly, whereas LMWH has to wear off.

Warfarin (such as Coumadin)

Warfarin is an anticoagulant that is taken in pill form. It is usually started while a person is still being treated with heparin because it takes several days for warfarin to build up to a level that's effective. When the warfarin is at a proper level, heparin is discontinued and treatment with warfarin continues. Studies show that warfarin reduces the risk of another blood clot.¹³

Typically, full-dose warfarin is given for at least 3 to 6 months or longer after pulmonary embolism to reduce the risk of having another blood clot. Treatment with anticoagulants may continue throughout your life if the risk of having another pulmonary embolism remains high. Talk with your doctor about whether continuing low-dose warfarin after your first treatment might be right for you.