Heparin is a naturally-occurring anticoagulant produced by basophils and mast cells. Heparin is also is widely used as an injectable anticoagulant.
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
Function; Why it is Recommended
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:
- Acute coronary syndrome, e.g., myocardial infarction
- Atrial fibrillation
- Deep-vein thrombosis and pulmonary embolism
- Cardiopulmonary bypass for heart surgery.
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:
- Adult respiratory distress syndrome (Reduces cell activation and accumulation in airways, neutralizes mediators and cytotoxic cell products, and improves lung function in animal models)
- Allergic encephalomyelitis
- Allergic rhinitis (Effects as for adult respiratory distress syndrome, although no specific nasal model has been tested)
- Arthritis (Inhibits cell accumulation, collagen destruction and angiogenesis)
- Asthma (As for adult respiratory distress syndrome, however it has also been shown to improve lung function in experimental models)
- Cancer (Inhibits tumour growth, metastasis and angiogenesis, and increases survival time in animal models)
- Delayed type hypersensitivity reactions
- Inflammatory bowel disease (Inhibits inflammatory cell transport in general)
- Interstitial cystitis (Effective in a human experimental model of interstitial cystitis)
- Transplant rejection (Prolongs allograph survival in animal models.)
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.
Side-Effects; Counter-Indicators and Warnings
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.
Rarer side-effects include alopecia
with chronic use.
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.