Heparin

Heparin is a widely used injectable blood thinner. It is used to treat and prevent deep vein thrombosis and pulmonary embolism (collectively known as venous thromboembolism) and is also used as part of the treatment of myocardial infarction and unstable angina. Heparin is used on the inside surfaces of various devices such as test tubes and kidney dialysis machines.

Common side effects include bleeding, pain at the injection site, and low blood platelets. Serious side effects include heparin induced thrombocytopenia. Greater care is needed in those with poor kidney function. Heparin appears to be safe for use during pregnancy and breastfeeding. It is a naturally occurring glycosaminoglycan.

Heparin's normal role in the body is unclear. Heparin is usually stored within the secretory granules of mast cells and released only into the vasculature at sites of tissue injury. It has been proposed that, rather than anticoagulation, the main purpose of heparin is defense at such sites against invading bacteria and other foreign materials. In addition, it is observed across a number of widely different species, including some invertebrates that do not have a similar blood coagulation system. It is a highly sulfated glycosaminoglycan. It has the highest negative charge density of any known biological molecule. In nature, heparin is a polymer of varying chain size. Unfractionated heparin (UFH) as a pharmaceutical is heparin that has not been fractionated to sequester the fraction of molecules with low molecular weight. In contrast, low-molecular-weight heparin (LMWH) has undergone fractionation for the purpose of making its pharmacodynamics more predictable. Often either UFH or LMWH can be used; in some situations one or the other is preferable.