How heparin works
Heparin is an anticoagulant polysaccharide (carbohydrate) that is stored in the body in the so-called mast cells and basophilic granulocytes – both subgroups of white blood cells (leukocytes) and important immune cells. If indicated, it can also be administered artificially from outside the body.
Heparin is an important component in the control of blood clotting. In the event of injuries to blood vessels, for example, this ensures that excessive blood loss is prevented. At the same time, however, the blood in intact vessels must always have optimum flow properties and must not clot spontaneously.
The most important endogenous inhibitor of blood clotting is the protein antithrombin. It inactivates the key enzyme thrombin in the coagulation system cascade so that fibrinogen dissolved in the blood cannot clump together to form solid fibrin. The anticoagulant effect of heparin is that it increases the effectiveness of antithrombin by a factor of about a thousand.
Heparins used therapeutically are divided into unfractionated heparin (high molecular weight heparin) and fractionated heparin (low molecular weight heparin). The latter is produced from unfractionated heparin. It has the advantage of having a longer effect and being better absorbed by the body (higher bioavailability).
When is heparin used?
Areas of application for high-dose heparin preparations are, for example
- venous thromboses (blood clots in a vein)
- acute coronary syndrome (unstable angina pectoris or acute myocardial infarction)
- Prevention (prophylaxis) of thrombosis during extracorporeal circulation (heart-lung machine) or dialysis
Low doses of heparin, on the other hand, are used to prevent thrombosis before and after an operation, in the event of injuries (e.g. with immobilization of an extremity) and in the event of prolonged bed rest.
How heparin is used
Systemic (= effective throughout the entire body) application is carried out as a heparin injection or infusion, i.e. bypassing the digestive tract (parenteral): The heparin injection is given under the skin (subcutaneous) or, more rarely, directly into a vein (intravenous). The infusion is administered directly into a vein (intravenous).
Heparin tablets would not be effective because the active ingredient is poorly absorbed by the body via the intestine.
Heparin can also be applied locally to the skin (for example as a gel), e.g. for injuries such as bruises and haematomas (but not on open wounds!). This has a decongestant effect. This local application is usually carried out once or twice a day for around one to two weeks.
Dosage in I.U.
In medical emergencies such as a heart attack, parenteral heparin (2-3 times 7,500 I.U.) and acetylsalicylic acid (ASA) must be administered immediately. To prevent thromboembolism, 5,000 to 7,000 IU of unfractionated heparin is then administered subcutaneously every eight to twelve hours.
Solubility
Heparin is produced as a salt (heparin sodium or heparin calcium) and then dissolved so that it can dissolve well in the liquid of a syringe, for example, and does not clump together.
What side effects does heparin have?
The most common side effect of heparin is unwanted bleeding. If the bleeding is severe, the effect of heparin must be stopped. Protamine is used for this purpose, which neutralizes the heparin.
Allergic reactions, reversible hair loss and an increase in liver enzymes are also possible.
Another frequently described side effect is heparin-induced thrombocytopenia (HIT for short). In thrombocytopenia, the number of blood platelets (thrombocytes) is reduced. This may be due to increased activation or clumping of the platelets.
In HIT type II, on the other hand, antibodies are formed against heparin. This can lead to severe clot formation (such as venous and arterial thrombosis, pulmonary embolism) if the platelets clump together. To prevent HIT, the number of platelets in the blood is checked weekly.
The risk of type II HIT is greater with unfractionated (high-molecular-weight) heparin than with fractionated (low-molecular-weight) heparin.
What should be considered when using heparin?
Heparin is not administered or only administered in very low doses in the following cases
- severe liver and kidney disease
- Suspicion of an injured or severely stressed vascular system (e.g. during certain operations, deliveries, organ sampling, gastrointestinal ulcers, high blood pressure)
- chronic alcoholism
If glycerol nitrate (vasodilating agents), antihistamines (allergy medication), digitalis glycosides (heart medication) or tetracyclines (antibiotics) are administered at the same time, the effect of heparin is reduced. Its dosage must therefore be adjusted (increased) accordingly.
Pregnancy and breastfeeding
Heparin is not compatible with the placenta or breast milk and can therefore be used during pregnancy and breastfeeding.
How to obtain medication with heparin
Heparin syringes and ampoules for the preparation of an injection or infusion solution must be prescribed or administered by a doctor.
How long has heparin been known?
In 1916, heparin was discovered by Jay McLean at John Hopkins University – the physician had isolated it from the liver of dogs. Today, heparin is extracted from pig intestinal mucosa or bovine lung.
