Anticoagulant — Indirect Thrombin Inhibitor Pregnancy: Anticoagulant treatment of pregnant women requires specialist involvement. Heparin does not cross the placenta and can be used during all trimesters of pregnancy if clinically needed, after risk/benefit evaluation. Reduced bone density has been reported with prolonged heparin treatment during pregnancy. Treatment doses are contraindicated in patients receiving neuraxial anaesthesia - delay epidural anaesthesia until at least 4-6 hours after the last intravenous treatment dose and 8-12 hours after the last subcutaneous treatment dose. This formulation contains benzyl alcohol, which may cross the placenta and cause accumulation and toxicity (metabolic acidosis); section 4.2 advises avoiding this formulation in pregnancy. Breast-feeding: heparin is not excreted in human milk and can be used during breast-feeding, though the benzyl alcohol content may cause accumulation and toxicity.

Unfractionated Heparin (IV)

Brand names: Heparin Sodium

Unfractionated heparin given by intravenous infusion is a rapidly acting, titratable anticoagulant used for acute venous thromboembolism, acute coronary syndromes, and during cardiac, vascular and extracorporeal procedures, especially where renal impairment or rapid reversibility is important.

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: 5,000-10,000 IU every 4 hours, or 500 IU/kg bodyweight daily as a continuous infusion in sodium chloride injection or dextrose injection

Route: intravenous (intermittent injection or continuous infusion)

Frequency: every 4 hours for intermittent intravenous administration; continuous over 24 hours for the infusion regimen

Treatment of thrombo-embolic disorders, intravenous administration. Doses should be individually adjusted according to coagulation tests. Dosage adjustment: it is recommended that dosages be adjusted to maintain a thrombin clotting time, whole blood clotting time or activated partial thromboplastin time 1.5 to 2 times that of control, on blood withdrawn 4-6 hours after the first injection or commencement of infusion and at similar intervals until the patient is stabilised. Subcutaneous alternative for treatment: initial dose 250 IU/kg bodyweight, further doses every 12 hours, individually adjusted according to coagulation tests. Prophylaxis (by subcutaneous injection, not intravenous): major elective surgery 5,000 IU 2 hours pre-operatively then every 8-12 hours post-operatively for 10-14 days or until the patient is ambulant, whichever is longer; following myocardial infarction 5,000 IU twice daily for 10 days or until the patient is mobile; other patients 5,000 IU every 8-12 hours. These standard prophylactic regimens do not require routine control. Prevention of clotting during haemodialysis (adults): an initial bolus dose of 1,000-5,000 IU followed by a continuous intravenous infusion of 1,000-2,000 IU per hour, adjusted to maintain clotting time at 40 minutes (the comparator symbol is lost in the source text - verify against the SPC). Children: standard treatment dosages should be given initially, with subsequent dosages and/or dosage intervals individually adjusted according to changes in thrombin clotting time, whole blood clotting time and/or activated partial thromboplastin time - no separate paediatric IU/kg figure is stated in the SPC. This formulation contains benzyl alcohol and must not be given to premature babies or neonates. Elderly: lower treatment dosages may be required, but standard treatment dosages should be given initially and then individually adjusted according to coagulation tests; no dosage alteration is needed for prophylaxis in the elderly. Pregnancy: this formulation contains the preservative benzyl alcohol which may cross the placenta, so use of this formulation should be avoided in pregnancy; if considered essential, give standard treatment dosages initially by continuous intravenous infusion, or every 12 hours by subcutaneous injection - intermittent intravenous injections are not advised. Suggested prophylactic dosage in pregnancy is 5,000 IU every 12 hours in early pregnancy increasing to 10,000 IU every 12 hours in the last trimester, maintaining plasma heparin below 0.4 IU/ml by specific anti-Xa assay; the dosage should be reduced during labour. Method of administration: for intravenous or subcutaneous injection - heparin should not be administered by intramuscular injection due to the risk of haematoma. Source product: Heparin (Mucous) Injection BP 1,000 IU. The SPC contains no ACS/PCI-specific or procedural weight-based bolus regimen.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC — 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, including uncontrolled severe hypertension, severe liver insufficiency, active peptic ulcer, intracranial haemorrhage or injuries and operations on the central nervous system, eyes and ears, and in women with abortus imminens (list not exhaustive)
Septic endocarditis
In patients receiving heparin for treatment rather than prophylaxis: locoregional anaesthesia in elective surgical procedures, and insertion of an epidural catheter (risk of epidural or spinal haematoma causing prolonged or permanent paralysis)
Contains benzyl alcohol 10 mg/ml - must not be given to premature babies or neonates due to the risk of gasping syndrome

Side effects

Haemorrhage and haematoma (common) - may present in any organ and at different degrees of severity, particularly when high doses are administered; major haemorrhage is uncommon but death or permanent disability has been reported
Erythema (common); injection site reaction (uncommon)
Transaminases increased (common); activated partial thromboplastin time prolonged beyond therapeutic range (uncommon)
Immune-mediated heparin-induced thrombocytopenia (type II) (uncommon) - largely manifests within 5 to 14 days of the first dose, may be associated with arterial and venous thrombosis; heparin must be discontinued in all cases. Non-immune heparin-associated thrombocytopenia (type I) also uncommon
Hyperkalaemia due to hypoaldosteronism (rare cases; listed uncommon) - patients at risk include those with diabetes mellitus or renal impairment
Skin necrosis, rash, urticaria, pruritus, anaphylactic reaction and hypersensitivity (uncommon); osteoporosis with long-term treatment (uncommon)

Interactions

Medicinal products affecting platelet function or the coagulation system - the combination should be avoided or carefully monitored (SPC section 4.4; section 4.5 was not captured in the fetched bundle)
Non-steroidal anti-inflammatory drugs (NSAIDs), platelet inhibitors and anticoagulants - increase the risk of epidural or spinal haematoma in patients undergoing peridural or spinal anaesthesia or spinal puncture
Concomitant intramuscular injections should be avoided due to the risk of haematoma

Clinical monograph

How it works

It binds antithrombin and greatly accelerates its inactivation of thrombin and activated factor Xa, producing immediate anticoagulation that can be reversed with protamine.

Prescribing in practice

Bleeding is the major hazard and the dose must be titrated to a coagulation target, with protamine available for reversal; avoid in active major bleeding and severe uncontrolled hypertension.
Heparin-induced thrombocytopenia is a serious immune-mediated complication, so monitor the platelet count and stop heparin if it falls significantly or new thrombosis occurs.
It can cause hyperkalaemia through aldosterone suppression, so check potassium in those at risk such as patients with diabetes or renal impairment, and weight-based nomograms guide infusion adjustment.

Monitoring

Monitor activated partial thromboplastin time (or anti-Xa) to titrate the infusion, with regular platelet counts for heparin-induced thrombocytopenia and potassium in at-risk patients.

Counselling the patient

Explain this is a closely monitored drip that thins the blood and is adjusted by blood tests.
Report any unusual bruising or bleeding promptly.
Tell staff of any past reaction to heparin.

Evidence & guidelines

Its use across thromboembolic and procedural anticoagulation is long-established and supported by the SPC and NICE guidance, with monitoring and reversal advantages over low molecular weight heparins in selected patients.

Reference: BCSH HIT guidelines; NICE NG158; 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.

Calculators

Pathways