[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [Heparins](https://durgical.com/en/pharmacology/classes/heparins/) › Heparin [Pharmacology](https://durgical.com/en/pharmacology/) · [Heparins](https://durgical.com/en/pharmacology/classes/heparins/) # Heparin An injectable anticoagulant that boosts antithrombin, the body's own clot brake. By vein it acts at once and is followed with the aPTT. Updated 2026-11-01 - Class: [Heparins](https://durgical.com/en/pharmacology/classes/heparins/) - Target: Antithrombin - ATC code: B01AB01 - WHO Model List of Essential Medicines Also called: unfractionated heparin, heparin sodium ◆**Antithrombin**Heparin ⓘ The figure shows antithrombin bound to the heparin pentasaccharide, the five-sugar sequence that binds and activates it (not a full heparin chain). **Target in 3D:** Antithrombin. PDB structure 1AZX (RCSB PDB, public domain). [View the structure at RCSB PDB](https://www.rcsb.org/structure/1AZX) · Drag to rotate · pinch to zoom ## Mechanism of action Heparin binds antithrombin and greatly speeds up its inhibition of clotting factors, mainly thrombin (IIa) and factor Xa. The binding happens through a specific five-sugar sequence (the pentasaccharide in the figure). Heparin does not dissolve existing clots, but it stops them from growing. - The heparin pentasaccharide binds antithrombin - Antithrombin then works far faster - Thrombin (IIa) and factor Xa are inactivated - Less fibrin: the aPTT lengthens and clots stop growing ## Pharmacokinetics **Absorption** Not taken by mouth; given into a vein or under the skin, not into muscle. **Metabolism** Not broken down by enzymes in the usual way; taken up by the liver and the reticuloendothelial system. **Elimination** Mainly cleared by that cellular uptake. **Half-life** Short and dose-dependent: about half an hour to two hours. **Onset and duration** Immediate by vein. ## Indications - Prevention and treatment of deep vein thrombosis. [Deep vein thrombosis →](https://durgical.com/en/conditions/deep-vein-thrombosis/) - Treatment of pulmonary embolism, as part of venous thromboembolism care. [Pulmonary embolism →](https://durgical.com/en/conditions/pulmonary-embolism/) - Acute ischaemic heart disease, including unstable angina and myocardial infarction. [Myocardial Infarction (Heart Attack) →](https://durgical.com/en/conditions/myocardial-infarction/) - Keeping catheters clot-free; selected situations in pregnancy. ## Adverse effects ### Common - Bleeding - Redness, pain or bruising at the injection site - Hair loss ### Serious (rare, important) - Heparin-induced thrombocytopenia (HIT), which can progress to thrombosis - Major bleeding - Osteoporosis with long-term, high-exposure use - Suppression of aldosterone production ## Contraindications - Current or past heparin-induced thrombocytopenia - Uncontrolled active bleeding - Allergy to heparin or pork products ## Key interactions **Aspirin, clopidogrel and other antiplatelet drugs** Add to bleeding risk. **NSAIDs** Add to bleeding risk. **Warfarin** Heparin can affect the prothrombin time, so INR samples are timed away from heparin given by vein. ## What is monitored - aPTT, which guides the regimen - Platelet count before and during treatment, looking for HIT - Signs of bleeding ## Memory aid Heparin does not fight the clot itself: it hands antithrombin a megaphone, and protamine is the plug that silences it. ## Test yourself Think of the answer, then tap the question to see it. ## How is unfractionated heparin reversed? With protamine sulfate, given slowly into a vein, which neutralises heparin. It only partly reverses the anti-Xa activity of low-molecular-weight heparins. ## A patient on heparin for 7 days has a sharp fall in platelets and a new leg clot. What is suspected? Heparin-induced thrombocytopenia with thrombosis: all heparin is stopped and a non-heparin anticoagulant is used. ## Does heparin dissolve a clot that is already there? No. It stops the clot from growing and new clots from forming; the body's own fibrinolysis then breaks the clot down. [Add to my cards (3)](https://durgical.app/estudiar/?add=/en/pharmacology/heparin/) ## Related drugs - [Warfarin](https://durgical.com/en/pharmacology/warfarin/) - [Rivaroxaban](https://durgical.com/en/pharmacology/rivaroxaban/) - [Dabigatran](https://durgical.com/en/pharmacology/dabigatran/) ## Related conditions - [Deep vein thrombosis](https://durgical.com/en/conditions/deep-vein-thrombosis/) - [Pulmonary embolism](https://durgical.com/en/conditions/pulmonary-embolism/) - [Myocardial Infarction (Heart Attack)](https://durgical.com/en/conditions/myocardial-infarction/) [← Back to the class: Heparins](https://durgical.com/en/pharmacology/classes/heparins/) Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given. Sources: [DailyMed - HEPARIN SODIUM- heparin sodium injection, solution](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=cb1c1e7a-c9ca-4a07-8833-e45ce436d287) (DailyMed (U.S. National Library of Medicine), 2026); [Heparin Injection: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a682826.html) (MedlinePlus (U.S. National Library of Medicine), 2025); [Partial Thromboplastin Time (PTT) Test: MedlinePlus Medical Test](https://medlineplus.gov/lab-tests/partial-thromboplastin-time-ptt-test/) (MedlinePlus (U.S. National Library of Medicine), 2026); [eEML - Electronic Essential Medicines List](https://list.essentialmeds.org/?query=heparin) (World Health Organization, 2025). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/pharmacology/heparin/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/heparin/