Heparin is an anticoagulant, which is a polymer formed by the alternating connection of two polysaccharides. It has anticoagulant effect in vivo and in vitro.
Heparin is a standard method to prevent thrombosis in pregnant women. Thrombotic status during pregnancy may increase the risk of thrombotic events by 3-4 times. Although there is a lack of clinical evidence to prove the effectiveness of heparin, experts have recommended the use of heparin for more than 20 years to prevent thrombosis, eclampsia and so on. In some cases of pregnant women without risk factors, anticoagulants are used to prevent coagulation or adverse pregnancy.
In addition to anticoagulation, heparin also has the following functions: ① make vascular endothelial cells release lipoprotein esterase, hydrolyze chyle particles and VLDL in blood, and play a role in regulating blood lipids; ② Inhibit the activity of inflammatory mediators and inflammatory cells, showing anti-inflammatory effect. ③ Inhibit the proliferation of vascular smooth muscle cells and the proliferation of vascular intima; ④ Inhibition of platelet aggregation (possibly through the indirect effect of inhibition of thrombin production), etc.
Common heparin types
According to the molecular weight, heparin can be divided into unfractionated heparin and low molecular weight heparin. Low molecular weight heparin is widely used in clinic at present. Heparin, bemi and Android are three non oral anticoagulants commonly used in clinic. They are mainly used to prevent and treat thrombosis or embolic diseases, such as myocardial infarction, thrombophlebitis, pulmonary embolism, etc. they are also used in hemodialysis, cardiopulmonary bypass, catheterization, microvascular surgery and other operations.
1. Low molecular weight heparin
Low molecular weight heparin (LMWH) is the first generation of low molecular weight heparin. It is a short chain preparation separated from unfractionated heparin or degraded by unfractionated heparin, and its general molecular weight is less than 7kda. Low molecular weight heparin maintains the antithrombotic effect of heparin and reduces the risk of bleeding. The half-life of anticoagulant factor Xa activity is long. It is defined as a class B drug for pregnancy by the U.S. Food and Drug Administration (FDA). It does not pass through the placenta, does not cause malformations and neonatal bleeding, and is safe during pregnancy; Not secreted in milk, safe during lactation. Low molecular weight heparin is also a mixture, with an average molecular weight ranging from 3000 to 5000kd.
2. Bemiheparin
Compared with the first generation low molecular weight heparin, due to the lower average molecular weight (3.6kda), the risk of thrombocytopenia and bleeding is lower, the half-life is longer, the activity of anticoagulant factor Xa is more persistent, and the bioavailability is higher. Therefore, a 3500IU of Bemiparin is about equal to the effect of 7000iu of the first generation low molecular weight heparin.
3. Android
Also known as fondaparinux sodium, it is a pure chemically synthesized pentosan methyl derivative (the active fragment of heparin and low molecular weight heparin), with a molecular weight of 1700kd. One 2.5mg of fondaparinux sodium is about 10000IU of the effect of the first generation low molecular weight heparin.