Enoxaparin !

A low-molecular-weight heparin injected under the skin. It acts mainly on factor Xa and needs no routine aPTT checks.

Updated 2026-11-01

Class: Heparins
Target: Antithrombin (and through it, mainly factor Xa)
ATC code: B01AB05
WHO Model List of Essential Medicines

Antithrombin (and through it, mainly factor Xa)Enoxaparin

The figure shows antithrombin bound to the heparin pentasaccharide, the five-sugar sequence through which enoxaparin binds and activates it (not an enoxaparin chain).

Target in 3D: Antithrombin (and through it, mainly factor Xa). PDB structure 1AZX (RCSB PDB, public domain). View the structure at RCSB PDB

Mechanism of action

Enoxaparin is made by breaking heparin into shorter chains. Like heparin, it binds antithrombin through a five-sugar sequence and speeds up its action. Most of its chains are too short to bridge antithrombin to thrombin, so it acts much more on factor Xa than on thrombin (a high anti-Xa to anti-IIa ratio). Less factor Xa means less thrombin and less fibrin.

Enoxaparin binds antithrombin through its pentasaccharide
Antithrombin then blocks factor Xa much faster
Short chains act little on thrombin: mainly anti-Xa effect
Less thrombin is made and clots grow less

Pharmacokinetics

Absorption: Under the skin it is almost completely absorbed; the anti-Xa effect peaks 3 to 5 hours after the injection.
Metabolism: In the liver, by desulfation and depolymerisation into less active pieces.
Elimination: Partly through the kidneys, so it builds up in severe kidney impairment.
Half-life: About 4.5 hours after one dose, up to about 7 hours after repeated doses (measured by anti-Xa activity).

Indications

Prevention of deep vein thrombosis after abdominal, hip or knee surgery and in bedbound medical patients. Deep vein thrombosis →
Treatment of deep vein thrombosis with or without pulmonary embolism, usually while warfarin is started. Pulmonary embolism →
Unstable angina, non-Q-wave myocardial infarction and STEMI, together with aspirin. Myocardial Infarction (Heart Attack) →

Adverse effects

Common

Bleeding and anaemia
Pain or bruising at the injection site
Mild drop in platelets
Raised liver enzymes

Contraindications

Active major bleeding
Heparin-induced thrombocytopenia within the past 100 days or with circulating antibodies
Hypersensitivity to enoxaparin, heparin or pork products

Key interactions

Other anticoagulants, aspirin and other platelet inhibitors, NSAIDs (including ketorolac), dipyridamole: Raise the risk of bleeding; such drugs are stopped beforehand when possible.
Neuraxial anaesthesia or epidural catheters: Risk of spinal haematoma; catheter timing follows the label and local protocol.

What is monitored

Complete blood count with platelets, and stool occult blood
Kidney function; anti-Xa levels in kidney impairment or when doses are uncertain
PT and aPTT are not adequate for monitoring it
Neurological checks after spinal or epidural procedures

Administration and safety

Deep subcutaneous injection, alternating left and right sides of the abdominal wall; never intramuscular
In the prefilled syringe the air bubble is not expelled, and the site is not rubbed afterwards
Not interchangeable unit for unit with heparin or other low-molecular-weight heparins
Syringes come in several strengths: the label is checked against the order (independent double check)

Nursing care

Baseline platelet count, haemoglobin and kidney function before starting
Watch the injection site and for any bleeding, including black stools and blood in urine
A falling platelet count or a new clot during treatment raises suspicion of heparin-induced thrombocytopenia
After epidural or spinal procedures, check for back pain, numbness or leg weakness
Teach self-injection technique when it continues at home

Pregnancy and breastfeeding

Human data do not suggest a higher risk of major birth defects; in pregnant women with mechanical heart valves, valve thrombosis has occurred and close monitoring is required.

Test yourself

Think of the answer, then tap the question to see it.

Why does enoxaparin act more on factor Xa than on thrombin?

Most of its chains are too short to bridge antithrombin and thrombin, which inhibiting thrombin needs; inhibiting Xa only needs the pentasaccharide.

Which test can follow enoxaparin when monitoring is needed?

Anti-factor Xa activity; PT and aPTT are not adequate.

How well does protamine reverse enoxaparin?

Only partly: it neutralises the anti-IIa effect, but the anti-Xa activity is never fully reversed (about 60% at most).

What happens to enoxaparin in severe kidney impairment?

Its clearance falls and exposure rises, so the regimen is adjusted and bleeding risk is watched closely.

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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 - ENOXAPARIN SODIUM injection, solution (DailyMed (U.S. National Library of Medicine), 2026); Enoxaparin Injection: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2025); eEML - Electronic Essential Medicines List (World Health Organization, 2025).

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Representative model, for educational purposes only.