Anticoagulants are often called 'blood thinners, however they do not acutally thin the blood. The drug alters certain chemicals in the blood to stop clots forming so easily. Anticoagulation treatment stops a clot in the lung from getting larger and prevents any new clots forming. It does not dissolve the clot

Heparin is usually the first medication given if a pulmonary embolism is suspected or diagnosed.  It will stop further clots forming. It may be given by an intravenous drip or low molecular weight heparin (LMWH) may be given by injection.

If your doctor thinks you have a life-threatening pulmonary embolism, you may be given an injection of a thrombolytic medicine which helps dissolve fresh blood clots.

Oral anticoagulants may be given after a course of LMWH  Both of these will be continued until blood tests show that the level of anticoagulant has reached the desired level. Once your blood tests show that the right levels have been reached then the heparin is stopped and the anticoagulant is continued as directed by the clinician. Some people may be assessed at being at a higher risk of another cloting event and may need long term treatment.

Not all anticoagulants require you to have LMWH first.

New treatments

Rivaroxaban is a new oral anticoagulant treatment and works by preventing your blood from clotting in a different way to Warfarin. It does this by blocking a substance in the blood which is involved in the development of blood clots, called factor Xa.

Rivaroxaban (Xalelto, Bayer) is now indicated as an option for the treatment of acute pulmonary embolism without symptomatic deep vein thrombosis and the prevention of Venous Thromboembolism (VTE) (NICE guidance TA 261)

It is also recommended as an option for treating deep vein thrombosis and preventing recurrent deep vein thrombosis and pulmonary embolism after a diagnosis of acute deep vein thrombosis in adults (NICE guidance TA 287) 

Dabigatran etexilate  (Pradaxa, Boehringer Ingleheim) is also recommended as an option for treating and preventing recurrent deep vein thrombosis and pulmonary embolism in adults. (NICE guidance TA  327)

Links to NICE guidelines can be found under the Guidance and Regulation section above