Anticoagulant Pregnancy: Heparin does not cross the placenta and can be used during all trimesters if clinically needed (specialist involvement required). However THIS formulation contains benzyl alcohol which may cross the placenta and cause accumulation/toxicity — this formulation should be avoided in pregnancy. Reduced bone density reported with prolonged use. Not excreted in human milk; can be used during breast-feeding.

Heparin (unfractionated)

Brand names: Heparin sodium

Unfractionated heparin is a parenteral anticoagulant used for treatment and prevention of venous thromboembolism and during procedures requiring rapid, adjustable anticoagulation.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: Treatment (IV): 5,000-10,000 IU every 4 hours, or 500 IU/kg bodyweight daily as a continuous infusion

Route: Intravenous or subcutaneous injection (not intramuscular — risk of haematoma)

Frequency: IV: every 4 hours or continuous infusion; SC treatment: initial 250 IU/kg then every 12 hours

For treatment or prevention of thrombo-embolic disorders. Treatment doses individually adjusted according to coagulation tests (aim to maintain thrombin clotting time, whole blood clotting time or APTT 1.5 to 2 times control on blood withdrawn 4-6 hours after first injection/commencement of infusion). Subcutaneous treatment: initial dose 250 IU/kg bodyweight, then every 12 hours adjusted by coagulation tests. Prophylaxis (subcutaneous): major elective surgery - 5,000 IU 2 hours pre-operatively then every 8-12 hours post-operatively for 10-14 days or until ambulant; following myocardial infarction - 5,000 IU twice daily for 10 days or until mobile; other patients - 5,000 IU every 8-12 hours (standard prophylactic regimens do not require routine control). Haemodialysis: initial bolus 1,000-5,000 IU then continuous infusion 1,000-2,000 IU per hour, adjusted to maintain clotting time. Contains benzyl alcohol - must not be given to premature babies or neonates (gasping syndrome).

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Hypersensitivity to the active substance or to any of the excipients
Current or history of immune-mediated heparin-induced thrombocytopenia (type II)
Active major haemorrhage and risk factors for major haemorrhage; generalised or local haemorrhagic tendency (incl. uncontrolled severe hypertension, severe liver insufficiency, active peptic ulcer, intracranial haemorrhage; abortus imminens)
Septic endocarditis
In patients on treatment doses: locoregional/neuraxial anaesthesia and epidural catheter insertion contraindicated (risk of epidural/spinal haematoma)
Benzyl alcohol preservative: must not be given to premature babies or neonates (gasping syndrome)

Side effects

Haemorrhage (common); haematoma (common)
Erythema (common); transaminases increased (common)
Immune-mediated heparin-induced thrombocytopenia type II (uncommon; typically within 5-14 days; may be associated with arterial and venous thrombosis)
Thrombocytopenia including non-immune type I (uncommon); hyperkalaemia due to hypoaldosteronism (uncommon)
Anaphylactic reaction, hypersensitivity, skin necrosis, urticaria, osteoporosis with long-term treatment (uncommon)

Interactions

Medicinal products affecting platelet function or the coagulation system (NSAIDs, platelet inhibitors, anticoagulants): avoid or carefully monitor — increased bleeding risk

Clinical monograph

How it works

It potentiates antithrombin, accelerating inactivation of thrombin and factor Xa to inhibit clot formation.

Prescribing in practice

Heparin-induced thrombocytopenia is a serious immune complication, so the platelet count must be monitored and heparin stopped if it occurs.
Bleeding is the main risk and can be reversed with protamine if needed.
It is contraindicated in active major bleeding and used with caution in renal or hepatic impairment and around invasive procedures.

Monitoring

Monitor the activated partial thromboplastin time (or anti-Xa) to guide therapeutic infusions and check the platelet count for heparin-induced thrombocytopenia.

Counselling the patient

Report unusual bruising, bleeding or blood in urine or stools.
Tell staff about any previous reaction to heparin.
Blood tests are used to adjust the dose and keep it in the right range.

Evidence & guidelines

Unfractionated heparin is long-established for thromboprophylaxis and treatment of thromboembolism, with monitoring and safety practice supported by NICE and MHRA guidance.

Reference: NICE NG89; ESC guidelines; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

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