Heparin belongs to the group of anticoagulants (Anticoagulants). It is a molecule produced in the human and animal organism and is used, among other things, for prevention (prevention) of thrombosis (Formation of blood clots with obstruction of blood vessels and subsequent reduced blood flow to organs) used.

Blood clotting

Greek.: Haemostasis = blood and stasis = stilling):
The Blood clotting is always important when a Injury to tissue has taken place. It makes the blood less fluid, so to speak, so that the injured area can be sealed and the bleeding stops as quickly as possible. A distinction is made between one primary hemostasis, where primarily the Platelets (Platelets) play a role and one secondary hemostasis, in which the so-called coagulation factors are the main actors. They will with numbered in roman numerals (I-XIII), mainly in the liver and ensure, in a cascade of activations connected in series, that fibrin molecules accumulate and form an insoluble network that - together with the platelets from primary hemostasis - closes the wound as best as possible.
Like almost every process, the Blood clotting strictly controlled become. Because if it runs out excessively, for example after Wound closure Not adequately stopped can lead to the formation of a Blood clot (thrombus) lead, which may be life-threatening embolism (Blockage of a blood vessel with subsequent reduced blood flow to the affected organ) can cause. The best known and feared example of this is probably pulmonary embolism.
In order to keep blood clotting within limits and to switch it off again at the right moment, there are various molecules, including this Antithrombin III. It binds to various coagulation factors (especially factors II and X) and thus inactivates them. Secondary hemostasis can no longer proceed adequately and coagulation is disturbed. Heparin binds to this antithrombin III and strengthens its activity, i.e. its anticoagulant effect.

Read more about this topic here: Blood clotting


Heparin is made up of many sugar molecules chained together Glycosaminoglycan. One distinguishes between unfractionated and low molecular weight (so fractionated) Heparin. The unfractionated heparin is longer (consists of more sugar molecules, namely between 40 and 50 sugar units) than the low molecular weight one, which consists of less than 18 sugar units.

Medical application

Heparin is produced in the human and animal organism. In humans it becomes of the so-called Mast cells synthesized and released. After discovering its great therapeutic benefits (it was discovered in 1916 and first used in humans in 1935) began to be extracted from beef lungs or pig intestines.
It is one of the most commonly used anticoagulant drugs (The coumarins also serve the same purpose, e.g. Marcumar, but they work through a different mechanism).
Heparin binds to the Coagulation inhibitor antithrombin III and strengthens its anticoagulant effect. Depending on the length of the chain, it works differently and sometimes has other properties.

Unfractionated heparin

Unfractionated heparin is long-chain and, with its binding to antithrombin III, ensures a Inhibition of coagulation factors II and X. During treatment with this heparin, the blood level of the drug must be monitored regularly as the Risk of overdose consists. Consequence would be increased tendency to bleed (by “liquefying” the blood, so to speak).
Ingestion: One intake as a tablet (peroral) is not possible in principle because heparin is in the gastrointestinal tract not absorbed becomes. So either it will intravenous (so with a syringe into a venous blood vessel) or subcutaneous (So with a syringe into the subcutaneous fatty tissue) applied. Unfractionated heparin has the best availability for intravenous use.

Low molecular weight heparin

Low molecular weight heparin is short-chain and inhibits with its bond Antithrombin III especially the Coagulation factor X. In the case of treatment with low molecular weight heparin, no close monitoring of the blood level is necessary.
Ingestion: It is injected subcutaneously.

Side effects

Both heparins carry the risk of increased bleeding tendency. In the event of an overdose of heparin, its effect can be largely neutralized (antagonized) by protamine. Protamine is the antidote (Greek: antidoto - what is given against it, so to speak the antidote) for heparin.

  • The risk of heparin-induced thrombocytopenia is greater with unfractionated heparin.
  • A distinction is made between type I and type II with this side effect, the latter being life-threatening and having to lead to immediate discontinuation of treatment with heparin. There is a sharp fall in the number of platelets (thrombocytopenia) in the blood and platelets clump together in the blood vessels, which can lead to reduced blood flow. Lethality (mortality) in heparin-induced thrombocytopenia type II is 30%.
  • Osteoporosis (fragile bones) is possible with long-term treatment with heparin
  • reversible hair loss

Read more on the topic: What are the causes of a cerebral hemorrhage


Heparin is used under the following therapeutic aspects:

  • Prevention (prevention) of thromboses and embolisms (e.g. after operations, since the risk of blood clots is particularly high here)
  • Therapy of acute embolisms (e.g. deep vein thrombosis, pulmonary embolism, vascular occlusion) Heart attack)


At least very careful treatment with heparin should be done in patients with

  • high blood pressure (hypertension)
  • Kidney function impairment (Renal failure)
  • previous thrombocytopenia
  • internal bleeding
  • increased tendency to bleeding (e.g. in cirrhosis of the liver, see: Clexane® and alcohol)


There are - besides those already mentioned above Coumarins (oral antocoagulants, i.e. anticoagulants that can be taken as tablets), but their effect is based on a completely different mechanism - other substances that can inhibit blood clotting

  • Fondaparinux - is a Heparin analog (thus has the same structure as heparin), which is produced synthetically (i.e. in the laboratory). It has the same mechanism of action as low molecular weight heparin (Inhibition of coagulation factor X), but cannot be antagonized by protamine. The Heparin-induced thrombocytopenia should not occur when using fondaparinux.
  • Hirudin and its derivatives (descendants) - they are derived from Leeches and directly inhibit the Factor II of blood clotting. They are either produced synthetically or applied to the patient through the direct application of leeches. E.g. used in patients with heparin-induced thrombocytopenia, who accordingly cannot tolerate heparin, but still require anticoagulant therapy.