Pharmacology · Class
Heparins !
Injectable anticoagulants that boost antithrombin, the body's own clot brake. By vein they act at once.
Updated 2026-11-01
What they are
Injectable anticoagulants made of sugar chains: unfractionated heparin (long, mixed chains) and low-molecular-weight heparins (shorter chains).
Mechanism of action
Heparin binds antithrombin through a five-sugar sequence (a pentasaccharide) and greatly speeds up its inhibition of clotting factors, mainly thrombin (IIa) and factor Xa. Unfractionated heparin acts on both about equally; low-molecular-weight heparins such as enoxaparin act much more on Xa than on IIa.
Target: Antithrombin (and through it, thrombin and factor Xa)
Drugs in this class
- HeparinAn injectable anticoagulant that boosts antithrombin, the body's own clot brake. By vein it acts at once and is…Antithrombin
- EnoxaparinA low-molecular-weight heparin injected under the skin. It acts mainly on factor Xa and needs no routine aPTT checks.Antithrombin (and through it, mainly factor Xa)
- FondaparinuxA synthetic five-sugar molecule, injected under the skin, that makes antithrombin block factor Xa. It has no effect on…Antithrombin (and through it, factor Xa only)
- DalteparinA low-molecular-weight heparin injected under the skin to prevent and treat venous clots, including clots linked to…Antithrombin (and through it, mainly factor Xa)
Others in the class
- enoxaparin
- dalteparin
- nadroparin
- tinzaparin
- bemiparin
Test yourself
Think of the answer, then tap the question to see it.
How does the activity of enoxaparin differ from that of unfractionated heparin?
Enoxaparin acts much more on factor Xa than on thrombin (a far higher anti-Xa to anti-IIa ratio), while unfractionated heparin acts on both about equally.
Which laboratory test follows unfractionated heparin, and which follows warfarin?
Unfractionated heparin: the aPTT. Warfarin: the prothrombin time reported as the INR.
What causes heparin-induced thrombocytopenia?
Antibodies against complexes of heparin and platelet factor 4. Platelets fall and clots can form (HITT); it usually starts about 5 to 9 days after heparin begins.
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 (DailyMed (U.S. National Library of Medicine), 2026); DailyMed - ENOXAPARIN SODIUM injection (DailyMed (U.S. National Library of Medicine), 2026); Heparin Injection: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2025); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).
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Representative model, for educational purposes only.