Anticoagulant (parenteral) 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; prophylactic doses require a minimum 4-6 hour delay. This formulation contains benzyl alcohol, which may cross the placenta and cause accumulation and toxicity (metabolic acidosis); §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 (UFH)

Brand names: Heparin Sodium

Unfractionated heparin (UFH) is a parenteral anticoagulant, given intravenously or subcutaneously, used for treatment and prevention of venous thromboembolism, in acute coronary syndromes, and during procedures such as cardiopulmonary bypass, particularly where rapid, titratable and reversible anticoagulation is needed.

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 of thrombo-embolic disorders - INTRAVENOUS: 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. Treatment - SUBCUTANEOUS (alternative route, different dose): initial dose 250 IU/kg bodyweight, then further doses every 12 hours. Prophylaxis - SUBCUTANEOUS only: 5,000 IU every 8-12 hours (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). All treatment doses individually adjusted according to coagulation tests

Route: Intravenous (intermittent injection or continuous infusion) or subcutaneous injection - each route has its own dose above and the two must NOT be interchanged. All prophylactic regimens are subcutaneous. Heparin must NOT be administered by intramuscular injection because of the risk of haematoma

Frequency: IV treatment: every 4 hours (intermittent) or continuous over 24 hours (infusion). SC treatment: every 12 hours. SC prophylaxis: every 8-12 hours

Max: No absolute ceiling is stated; treatment dosage is titrated to a thrombin clotting time, whole blood clotting time or activated partial thromboplastin time 1.5 to 2 times that of control. The SPC distinguishes prophylactic doses (up to 15,000 IU/day) from treatment doses (above 15,000 IU/day) for neuraxial-procedure timing

Source product: Heparin (Mucous) Injection BP 1,000 IU; indication is the treatment or prevention of thrombo-embolic disorders. DOSAGE ADJUSTMENT: adjust dosages to maintain a thrombin clotting time, whole blood clotting time or APTT 1.5 to 2 times control, on blood withdrawn 4-6 hours after the first injection or commencement of infusion, and at similar intervals until the patient is stabilised. Standard prophylactic regimens do not require routine control. Following myocardial infarction (PROPHYLAXIS, subcutaneous): 5,000 IU twice daily for 10 days or until the patient is mobile - this is VTE prophylaxis post-MI and is NOT an ACS anticoagulation regimen. Prevention of clotting during haemodialysis (adults): initial bolus 1,000-5,000 IU followed by continuous intravenous infusion 1,000-2,000 IU per hour, adjusted to maintain clotting time above 40 minutes (the comparator symbol is degraded in the fetched text - verify against the SPC). CHILDREN: standard treatment dosages should be given initially, then subsequent dosages and/or dosage intervals individually adjusted according to changes in thrombin clotting time, whole blood clotting time and/or APTT - no separate paediatric IU/kg figure is stated, hence paedDose is null; 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. 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, keeping plasma heparin below 0.4 IU/mL by specific anti-Xa assay; the dosage should be reduced during labour and the standard prophylactic dosage is suitable in the puerperium. MONITORING: platelet count should be measured before starting treatment and periodically thereafter because of the risk of immune-mediated heparin-induced thrombocytopenia (type II). The SPC contains no ACS/PCI-specific or procedural weight-based bolus regimen and no ACT targets.

Dose adjustments

Renal

No numeric renal dose adjustment is stated. §4.4 advises that care should be taken when heparin is administered to patients with an increased risk of bleeding complications, hypertension, or renal or hepatic insufficiency; patients with renal impairment are also at increased risk of hyperkalaemia due to hypoaldosteronism.

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 (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 (stated in §4.4; §4.5 itself was truncated 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 (factor IIa) and factor Xa, inhibiting fibrin formation; its effect is short-lived and reversible with protamine.

Prescribing in practice

Heparin-induced thrombocytopenia is a serious immune-mediated complication, so monitor the platelet count and stop heparin if it occurs.
Bleeding is the principal risk and the therapeutic intravenous infusion requires APTT-guided dose adjustment; protamine sulphate is the specific antidote.
Caution in renal and hepatic impairment, and with prolonged use hyperkalaemia and osteoporosis can occur.

Monitoring

Monitor the APTT (or anti-Xa) to guide therapeutic dosing and the platelet count for heparin-induced thrombocytopenia, with potassium on prolonged use.

Counselling the patient

Explain that the dose is adjusted by regular blood tests during treatment.
Report any unusual bruising, bleeding, or new limb swelling or pain.
Mention any previous reaction to heparin before treatment.

Evidence & guidelines

Unfractionated heparin with APTT monitoring and platelet surveillance for heparin-induced thrombocytopenia is established UK anticoagulation practice.

Reference: BCSH 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