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Anticoagulant / ACS / PCI Pregnancy: §4.6, verbatim: 'Heparin is not contraindicated in pregnancy. Heparin does not cross the placenta or appear in breast milk. The decision to use heparin in pregnancy should be taken after evaluation of the risk/benefit in any particular circumstances. Osteoporosis has been reported with prolonged heparin treatment during pregnancy. Particular caution is required at the time of delivery. Due to the risk of uteroplacental haemorrhage, heparin treatment should be stopped at the onset of labour. If epidural anaesthesia is envisaged, heparin treatment should be suspended whenever possible.' Use in women with threatened abortion is contraindicated, as is epidural anaesthesia during birth in women treated with heparin. §4.4 adds that heparin resistance 'is also often encountered in acutely ill patients, in patients with malignancy and during pregnancy or the post-partum period', and that large amounts of the benzyl alcohol excipient can build up in pregnant or breast-feeding women and cause metabolic acidosis.

Unfractionated Heparin (ACS / PCI)

Brand names: Heparin Sodium (various)

Used in: Venous Thromboembolism (DVT & PE)

Unfractionated heparin is a parenteral anticoagulant used in acute coronary syndromes and during percutaneous coronary intervention, valued for its rapid onset, short half-life and reversibility.

Adult dose

Dose: Unstable angina pectoris (the ACS indication of this page) — adults: loading dose 5,000 units intravenously, then maintenance 1,000–2,000 units/hour by continuous intravenous infusion, or 5,000–10,000 units 4-hourly by intermittent intravenous injection, with the dose adjusted to maintain an APTT value 1.5–2.5 × the midpoint of the normal range or control value. SCOPE OF THIS FIGURE: this is the UK SPC's licensed regimen for unstable angina pectoris (stated in §4.2 as one grouped indication with deep vein thrombosis, pulmonary embolism and acute peripheral arterial occlusion). It is NOT a PCI regimen — this label states no procedural bolus and no cath-lab ACT target for percutaneous coronary intervention, so the PCI half of this page remains unsourced. Note also that §4.2 gives a SEPARATE weight-based regimen for 'Children and small adults' (50 units/kg loading, then 15–25 units/kg/hour) — see notes.
Route: Intravenous — §4.2, verbatim: 'By continuous intravenous infusion in 5% glucose or 0.9% sodium chloride or by intermittent intravenous injection. The intravenous injection volume of heparin injection should not exceed 15ml. As the effects of heparin are short-lived, administration by intravenous infusion is preferable to intermittent intravenous injections.' §4.3, verbatim: 'Heparin should not be administered by intramuscular injection or after major trauma.'
Frequency: Continuous intravenous infusion (alternatively 4-hourly by intravenous injection), titrated to coagulation testing. §4.2, verbatim: 'Daily laboratory monitoring (ideally at the same time each day, starting 4-6 hours after initiation of treatment) is essential during full-dose heparin treatment, with adjustment of dosage to maintain an APTT value 1.5-2.5 x midpoint of normal range or control value.'
Max: No absolute maximum dose is stated for this indication — the regimen is titrated to APTT rather than capped. The upper end of the §4.2 maintenance range for this indication is 2,000 units/hour by continuous intravenous infusion, or 10,000 units 4-hourly by intermittent intravenous injection. The only other ceiling in §4.2 is an administration limit, not a dose limit: 'The intravenous injection volume of heparin injection should not exceed 15ml.' The '10,000 units may be required in severe pulmonary embolism' loading figure is a PULMONARY EMBOLISM figure and is deliberately not carried across as this indication's ceiling.
SCOPE — WHAT IS AND IS NOT SOURCED. §4.1 of the fetched SPC reads, verbatim: 'Treatment of deep vein thrombosis, pulmonary embolism, unstable angina pectoris and acute peripheral arterial occlusion. In extracorporeal circulation and haemodialysis.' Unstable angina pectoris is therefore a licensed indication of this product and §4.2 carries an explicit adult regimen for it by this page's own route, so the ACS half of this page is now sourced. PCI IS STILL NOT SOURCED: nothing in this label describes percutaneous coronary intervention, and the only weight-based/ACT regimen in it belongs to CARDIOPULMONARY BYPASS, which is a different procedure and must not be reused as a PCI bolus. A clinician must still supply a PCI-specific procedural source (weight-based bolus and cath-lab ACT targets) or the page should be re-scoped. || SMALL ADULTS — SOURCED IN THIS SPC. §4.2 does not leave the fixed adult band as the only option: verbatim, 'Children and small adults: Loading dose: 50 units/kg intravenously Maintenance: 15-25 units/kg/hour by intravenous infusion, or 100 units/kg 4-hourly by intravenous injection'. Use that weight-based regimen for small adults rather than applying the flat 1,000–2,000 units/hour band to a low body weight. paedDose is nevertheless left null: this is an adult cardiology page, the paediatric figures above are not a paediatric ACS or PCI regimen, and §4.3 bars this presentation from the youngest patients — verbatim, 'Must not be given to premature babies or neonates (contains benzyl alcohol)'; §4.4 adds 'This medicine contains 10mg/ml benzyl alcohol... Do not give to your newborn baby (up to 4 weeks old), unless recommended by your doctor. Do not use for more than a week in young children (less than 3 years old), unless advised by your doctor.' Verify all under-18 dosing against a children's formulary. || DOSE ADJUSTMENT. Elderly — §4.2, verbatim: 'Dosage reduction may be advisable.' §4.4 adds that 'The risk of bleeding is increased with severe renal impairment and in the elderly (particularly elderly women).' Heparin resistance — §4.2, verbatim: 'Patients with altered heparin responsiveness or heparin resistance may require disproportionately higher doses of heparin to achieve the desired effect.' §4.4 quantifies it: 'Heparin resistance, defined as an inadequate response to heparin at a standard dose for achieving a therapeutic goal occurs in approximately 5 to 30% of patients', and lists antithrombin III activity below 60% of normal, active infection, advanced age, thrombocytopenia, plasma albumin ≤ 35g/dl and relative hypovolaemia among the predisposing factors. Hypersensitivity precaution — §4.4, verbatim: 'Although heparin hypersensitivity is rare, it is advisable to give a trial dose of 1,000 I.U. in patients with a history of allergy.' || FIGURES DELIBERATELY NOT CARRIED ACROSS INDICATIONS. Severe pulmonary embolism loading dose (10,000 units); cardiopulmonary bypass (initially 300 units/kg intravenously, adjusted to keep the activated clotting time in the range 400–500 seconds); haemodialysis and haemofiltration (initially 1,000–5,000 units, maintenance 1,000–2,000 units/hour, adjusted to maintain clotting time greater than 40 minutes). These are recorded here only so they cannot be mistaken for the ACS or PCI dose. || TRUNCATION. §4.4/§4.5 (§4.5 is absorbed into the warnings text rather than fetched separately) and §4.8 both end at the source-fetch limit, so the interaction and adverse-effect lists below are incomplete — the §4.5 text stops mid-sentence at 'Increased risk of bleeding with oral anticoagulants,'.

Dose adjustments

Renal

§4.4, verbatim: 'In patients with advanced renal or hepatic disease, a reduction in dosage may be necessary. The risk of bleeding is increased with severe renal impairment and in the elderly (particularly elderly women).' No numeric reduction and no eGFR-banded regimen are given. Patients with chronic renal failure are also at increased risk of hyperkalaemia from heparin-induced hypoaldosteronism.

Hepatic

§4.4, verbatim: 'In patients with advanced renal or hepatic disease, a reduction in dosage may be necessary.' Severe liver disease (including oesophageal varices) is a contraindication under §4.3. No numeric reduction is given.

Dose independently re-sourced from UK Summary of Product Characteristics (SPC) via the eMC — clinician-reviewed. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

  • Hypersensitivity to the active substance or to any of the excipients listed in section 6.1
  • Must not be given to premature babies or neonates (this formulation contains benzyl alcohol)
  • Heparin should not be administered by intramuscular injection or after major trauma
  • Patients who consume large amounts of alcohol, who are sensitive to the drug, who are actively bleeding, or who have haemophilia or other bleeding disorders, severe liver disease (including oesophageal varices), purpura, severe hypertension, active tuberculosis or increased capillary permeability
  • Patients with present or previous thrombocytopenia; and previous heparin-induced skin necrosis, which contraindicates further heparin by either the subcutaneous or intravenous route because of the risk of thrombocytopenia
  • Surgery of the brain, spinal cord and eye; procedures at sites where there is a risk of bleeding; recent surgery; lumbar puncture or regional anaesthetic block (special hazard of post-operative haemorrhage)
  • In patients receiving heparin for treatment rather than prophylaxis: locoregional anaesthesia in elective surgical procedures — if such a procedure is planned, heparin should be stopped and the procedure delayed until the aPTT has returned to normal (risk of epidural or spinal haematoma causing prolonged or permanent paralysis)
  • Epidural anaesthesia during birth in pregnant women treated with heparin; and use in women with threatened abortion
  • Concomitant use of intravenous diclofenac with heparin (including low dose heparin)
  • Relative — assess risks and benefits carefully in patients with a bleeding tendency or an actual or potential bleeding site, e.g. hiatus hernia, peptic ulcer, neoplasm, bacterial endocarditis, retinopathy, bleeding haemorrhoids, suspected intracranial haemorrhage, cerebral thrombosis. Menstruation is not a contraindication

Side effects

  • Haemorrhage — the principal risk (see also the overdose and special warnings sections of the SPC)
  • Thrombocytopenia, observed occasionally, and reported more frequently with bovine-derived than porcine-derived heparin. Type I is frequent, mild (usually above 50 x 10^9/L) and transient, occurring within 1–5 days. Type II is less frequent but often severe (usually below 50 x 10^9/L), immune-mediated, occurring after a week or more (earlier in patients previously exposed), associated with a platelet-aggregating antibody and thromboembolic complications from platelet-rich thrombi (the 'white clot syndrome'), which may precede the thrombocytopenia. Heparin should be discontinued immediately
  • Heparin-induced thrombocytopenia (HIT) and HIT with thrombosis (HITT) can occur up to several weeks after discontinuation of heparin; pulmonary embolism has been reported as a thromboembolic complication
  • Endocrine: adrenal insufficiency secondary to adrenal haemorrhage (rarely); hypoaldosteronism causing raised plasma potassium, with clinically significant hyperkalaemia occurring rarely, particularly in chronic renal failure and diabetes mellitus
  • Hepatic: increased serum transaminase values, usually resolving on discontinuation
  • Immune system: hypersensitivity reactions are rare — urticaria, conjunctivitis, rhinitis, asthma, cyanosis, tachypnoea, feeling of oppression, fever, chills, angioneurotic oedema and anaphylactic shock. In some instances the precipitating agent proves to be the preservative rather than the heparin
  • Metabolic: release of lipoprotein lipase into plasma, with rebound hyperlipidaemia possible after heparin withdrawal
  • Musculoskeletal: prolonged dosing over many months may cause osteoporosis and fractures in the vertebrae and ribs; significant bone demineralisation reported in women taking more than 10,000 I.U. per day for three months or longer
  • Reproductive: priapism has been reported
  • Skin: local irritation and skin necrosis may occur but are rare
  • This side-effect list may be incomplete — check the full SPC.

Interactions

  • Aspirin and other NSAIDs — §4.5, verbatim: 'Analgesics: Drugs that interfere with platelet aggregation e.g. aspirin and other NSAIDs should be used with care.' Directly relevant on an ACS page, where heparin is co-prescribed with antiplatelet therapy
  • Ketorolac and intravenous diclofenac — §4.5, verbatim: 'Increased risk of haemorrhage with; - Ketorolac - Intravenous diclofenac (refer to section 4.3) Avoid concomitant use of either ketorolac or intravenous diclofenac, even with low-dose heparin.' Concomitant intravenous diclofenac is an outright contraindication under §4.3
  • Oral anticoagulants — §4.5, verbatim: 'Anticoagulants, platelet inhibitors, etc: Increased risk of bleeding with oral anticoagulants,' — the section ends at the source-fetch limit at this point, so the remainder of the anticoagulant/platelet-inhibitor list was not retrieved
  • Non-steroidal anti-inflammatory drugs, platelet inhibitors and anticoagulants — §4.4: concomitant use increases the risk of spinal or epidural haematoma in patients undergoing peridural or spinal anaesthesia or spinal puncture
  • Potassium-sparing drugs — §4.4: added to heparin's suppression of aldosterone secretion, they increase the risk of hyperkalaemia
  • Drugs affecting platelet function or the coagulation system — §4.4, verbatim: 'Drugs affecting platelet function or the coagulation system should in general not be given concomitantly with heparin (see section 4.5).'
  • This interaction list may be incomplete — check the full SPC.

Monitoring

  • APTT — §4.2, verbatim: 'Daily laboratory monitoring (ideally at the same time each day, starting 4-6 hours after initiation of treatment) is essential during full-dose heparin treatment, with adjustment of dosage to maintain an APTT value 1.5-2.5 x midpoint of normal range or control value'
  • Platelet count — §4.4, verbatim: 'Platelet counts should be measured in patients receiving heparin treatment for longer than 5 days and the treatment should be stopped immediately in those who develop thrombocytopenia.' Patients presenting with thrombocytopenia or thrombosis after heparin has been stopped should be evaluated for HIT or HITT
  • Plasma potassium — §4.4: measure before starting heparin in patients at risk of hyperkalaemia (diabetes mellitus, chronic renal failure, pre-existing metabolic acidosis, a raised plasma potassium, or taking potassium-sparing drugs), and in all patients treated for more than 7 days; the risk appears to increase with duration of therapy but is usually reversible
  • Coagulation time in patients undergoing major surgery — §4.4, verbatim: 'patients show an individual response to heparin, and it is therefore essential that the effect of therapy on coagulation time should be monitored in patients undergoing major surgery'
  • Neurological status where heparin is given in the context of peridural or spinal anaesthesia — §4.4, verbatim: 'extreme vigilance and frequent monitoring must be exercised to detect any signs and symptoms of neurologic impairment, such as back pain, sensory and motor deficits and bowel or bladder dysfunction'
  • Note: the fetched SPC has no dedicated monitoring section; the items above are drawn from §4.2 and §4.4, and §4.4 ends at the source-fetch limit

Clinical monograph

How it works

It binds antithrombin and greatly accelerates its inactivation of thrombin (factor IIa) and factor Xa, thereby inhibiting fibrin formation and thrombus propagation.

Prescribing in practice

  • Bleeding is the major risk and should be weighed against thrombotic benefit; its anticoagulant effect can be reversed with protamine if serious haemorrhage occurs.
  • Heparin-induced thrombocytopenia is an important immune-mediated complication, so platelet counts should be monitored and the drug stopped if it is suspected.
  • It is contraindicated in active major bleeding and in known heparin-induced thrombocytopenia, with caution near surgery or recent trauma.

Monitoring

Monitor the activated partial thromboplastin time (or anti-Xa) for therapeutic intravenous infusions, together with platelet count and haemoglobin, adjusting the rate to target.

Counselling the patient

  • This is a hospital anticoagulant that increases the risk of bleeding.
  • Report any unusual bruising, bleeding or new pain or swelling.
  • Tell the team about any prior reaction to heparin.

Evidence & guidelines

Unfractionated heparin is established standard anticoagulation in acute coronary syndromes and PCI, and its use is embedded in NICE and ESC guidance for these settings.

Reference: ESC STEMI 2023; ESC NSTE-ACS 2020; BSH HIT Guidelines 2012; NICE NG185; SPC Heparin Sodium; 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).

Related

Curated clinical cross-links plus same-class fallbacks.

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