Heparin, discovered in 1916, is one of the oldest drugs still in widespread clinical use. Prior to 1933, heparin was available, but in small amounts, and was extremely expensive, toxic, and, as a consequence, of no medical value.
Pharmaceutical grade heparin is derived from mucosal tissues of slaughtered meat animals such as porcine (pig) intestine or bovine lung.
Heparin acts as an anticoagulant, preventing the formation of clots and extension of existing clots within the blood. While heparin does not break down clots that have already formed, it allows the body's natural clot lysis mechanisms to work normally to break down clots that have already formed.
Heparin is used for anticoagulation for the following conditions:
There is a great deal of potential for the development of heparin-like structures as drugs to treat a wide range of diseases, in addition to their current use as anticoagulants. Some conditions that appear to be sensitive to heparin include:
Heparin is given parenterally, as it is degraded when taken by mouth. It can be injected intravenously or subcutaneously. Intramuscular injections are avoided because of the potential for forming hematomas.
Because of its short biologic half-life of approximately one hour, heparin must be given frequently or as a continuous infusion. However, the use of low molecular weight heparin (LMWH) has allowed once daily dosing, thus not requiring a continuous infusion of the drug. If long-term anticoagulation is required, heparin is often used only to commence anticoagulation therapy until the oral anticoagulant Warfarin takes effect.
A serious side-effect of heparin is heparin-induced thrombocytopenia (HIT syndrome). HITS is caused by an immunological reaction that makes platelets a target of immunological response, resulting in the degradation of platelets. This is what causes thrombocytopenia. This condition is usually reversed on discontinuation, and can generally be avoided with the use of synthetic heparins. There is also a benign form of thrombocytopenia associated with early heparin use, which resolves without stopping heparin.
As with many drugs, overdoses of heparin can be fatal.
At the time of writing (2008), Heparin is under investigation by the FDA because of its apparent role in 21 deaths. The cause has not been identified but officials are looking to China for possible sources of contaminated raw materials.
Aspirin followed by heparin may be used if a clotting abnormality is present.