All About Heparins and How They’re Administered

Low-molecular weight heparins have less inhibitory activity than unfractionated heparins. However, they also have a lower risk of bleeding. Learn all about heparins in this article!
All About Heparins and How They’re Administered

Last update: 13 January, 2021

Heparins are drugs that are administered intravenously and have very powerful anticoagulant effects. We talk of heparins in plural because there are two types: low-molecular-weight heparins (LMWH) and standard or unfractionated heparins (UFH).

Doctors administer them parenterally because the body doesn’t absorb them as well orally. Also, digestive enzymes inactivate them; therefore, they’re only administered intravenously.

Among the different routes of parenteral administration, subcutaneous is the classic form for both low-molecular-weight and unfractionated heparins. Medical professionals use an intravenous line (IV line) to administer UFHs in emergency situations.

All about heparins: unfractionated heparins or UFHs

A blood sample for a blood test.

This type of heparin consists of a heterogeneous mixture of sulphated polysaccharides. These biomolecules can vary in both size and weight.

They weigh between 6,000 and 40,000 daltons, with an average weight of 15,000 daltons. The chains that make up this type of heparin contain glucosamine and sulfate glucuronide or iduronic acid.

Low-molecular-weight heparins or LMWHs

As for low-molecular-weight heparins, they stem from various methods of fractionation or depolymerization of polymeric heparin. They also consist of polysaccharide chains. However, their average molecular weight is much lower, between 4,000 and 5,000 daltons.

Therapeutic indications

As we already mentioned, doctors resort to these drugs in situations that require fast and short-lasting anticoagulant action. They’re mostly used in the prevention and treatment of deep vein thrombosis (DVT), as well as in both high and low-risk surgeries.

Regarding the treatment of deep vein thrombosis, whether it causes pulmonary embolism or not, doctors start with heparin until the patient’s prothrombin time (PT) stabilizes. After that, doctors continue administering oral anticoagulants. Furthermore, doctors can resort to either type of heparin for this purpose.

However, low-molecular-weight heparin has a number of advantages. It has fewer adverse effects and it can be administered in a single daily dose. This dose depends on the patient’s body weight. Thus, doctors don’t need to control the antithrombotic effect, since it doesn’t interact with plasma proteins.

All about heparins: mechanism of action

A blood clot.

In order to fulfill its therapeutic goal and trigger antithrombotic and anticoagulant effects, heparins are capable of inhibiting factor X and prothrombin or factor II, respectively.

These factors are closely related to clot and thrombi formation. Therefore, by inhibiting these factors, heparins prevent their formation.

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

Side effects of heparins

Like all drugs, heparins can cause many different side effects. However, low-molecular-weight heparins have fewer side effects than unfractionated ones.

Side effects are the undesirable and unintended events that a patient can expect when they start treatment with a drug. In this sense, the most common side effects of the use of these drugs are:

  • Hemorrhages. They aren’t as common when the treatment is preventive, since the doses are lower. The dose should be adjusted in patients with kidney problems, since it favors the appearance of this adverse effect.
  • Thrombocytopenia. This complication isn’t dose-related, as is the case with bleeding. Likewise, it isn’t related to age or the route of administration. It’s a response that varies from person to person.
  • Skin necrosis.
  • Hypersensitivity reactions
  • Hypoaldosteronism. Low levels of the hormone aldosterone.

Finally, we need to mention that the two types of heparins can cause osteoporosis. However, this effect is less likely to occur in long-term treatments.


Both low-molecular-weight and unfractionated heparins are drugs that can prevent thrombi and clot formation. They’re usually indicated in surgery and in the treatment and prevention of deep vein thrombosis.

These drugs are powerful and can cause side effects. You can consult with your doctor or pharmacist if you have questions about this drug.

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  • Arone, K. M. B., Oliveira, C. Z. de, Garbin, L. M., Reis, P. E. D. dos, Galvão, C. M., & Silveira, R. C. de C. P. (2012). Thrombotic obstruction of the central venous catheter in patients undergoing hematopoietic stem cell transplantation. Revista Latino-Americana de Enfermagem.
  • Rodriguez Moral, N. E. (1972). TROMBOSIS VENOSA. Revista Cubana de Cirugia.
  • Rocha Hernando, E. (2014). Historia de la heparina. Angiología.
  • Trejo I., C. (2004). Anticoagulantes: Farmacología, mecanismos de acción y usos clínicos. Cuadernos de Cirugía.
  • Ricardo Sebastián Alba Posse., Erika Roxana Ctay., Roberto Alejandro Toledo., M. L. V. C. (2006). Heparina De Bajo Peso Molecular Versus Heparina No. Medicina de Posgrado de La VI Cátedra de Medicina.