Heparin: what is it and how is it administered?

Heparins are drugs that are given intravenously and that they have a very potent anticoagulant effect. We speak of plural heparins because there are two types: low molecular weight heparin and standard or unfractionated heparin.

They are administered parenterally because orally absorbed very poorly. In addition, digestive enzymes inactivate them. Therefore, they are only administered by injection.

Among the different routes of parenteral administration, The subcutaneous is the classic form of administration, both of low molecular weight and non-fractionated heparin. The intravenous route is used to administer unfractionated heparin in emergency situations.

Unfractionated heparin or HNF

This type of heparins They are formed by a heterogeneous mixture of different polysaccharides. These biomolecules can vary in both size and weight.

The weight is between 6,000 and 40,000 daltons, the average weight being 15,000 daltons. The chains that constitute this type of heparins contain glucosamine and glucuronide or sulfated iduronic acid.

Low molecular weight heparin or LMWH

As for low molecular weight heparins, these come from the fracture of the previous ones. They are also formed by polysaccharide chains, but the average molecular weight is much lower; it is between 4,000 and 5,000 daltons.

Therapeutic indications

Heparins, as we know, they are used in situations where a rapid and short-acting anticoagulant action is needed. The most characteristic cases are the prevention and treatment of deep vein thrombosis, as well as in surgeries, both high and low risk.

As for the treatment of deep vein thrombosis, whether or not you have pulmonary embolism, this starts with heparin until protombin time stabilizes. Then, the administration of oral anticoagulants is continued. In addition, any of the two types of heparins that we have mentioned can be used for this purpose.

However, low molecular weight heparin It presents a number of advantages, as less adverse effects and the possibility of administering it in a single daily dose. This dose is based on the patient's body weight, so it is not necessary to control the antithrombotic effect, since it does not interact with plasma proteins.

Discover: What is a thrombosis and how to prevent it?

How do heparins carry out their effect on the body?

In order to fulfill its therapeutic objective and trigger its antithrombotic and anticoagulant effect, heparins are capable of inhibiting factor Xa and factor IIa, respectively.

These factors are closely related to the formation of clots and thrombi. Therefore, by inhibiting their action, heparins prevent their formation.

Low molecular weight heparins have a lower inhibitory activity than unfractionated However, they also have a lower risk of bleeding.

Adverse effects of heparins

Like all medications, Heparin treatment may be accompanied by a series of adverse effects. However, those with low molecular weight have fewer adverse reactions than non-fractional ones.

Adverse effects are all undesirable and unintended events that occur as expected with the use of a medication. In this sense, the most common adverse effects with the use of heparins They are:

  • Hemorrhages: They are not as frequent when treatment is focused on prevention, since the doses are lower. In patients with kidney problems, the dose should be adjusted, since it favors the appearance of this adverse effect.
  • Thrombocytopenia: It is not dose related, as is the case with bleeding. Nor is it related to age or the route of administration. It is a response that varies from one person to another.
  • Cutaneous necrosis.
  • Hypersensitivity reactions
  • Hypoaldosteronism: low levels of the hormone aldosterone.

Finally, mention that the two types of heparins they can produce an osteoporosis picture. However, when the treatments are long term, this effect is reduced.

Read also: Risk of post-surgical hemorrhage


Heparins, both low molecular weight and unfractionated, are medications are used to prevent the formation of thrombi and clots. Above all, they are indicated in surgery and in the treatment and prevention of deep vein thrombosis.

They are drugs with a very potent action and they are not exempt from producing adverse effects. You can ask your doctor or pharmacist any questions you have about this type of medication.