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Anticoagulant / ACS / PCI Pregnancy: Safe in all trimesters — does not cross placenta. Preferred anticoagulant in pregnancy (with LMWH). Switch to UFH near term for reversibility.

Unfractionated Heparin (ACS / PCI)

Brand names: Heparin Sodium (various)

Adult dose

Dose: ACS (NSTEMI/STEMI): IV bolus 60-70 units/kg (max 5000 units), then infusion 12-15 units/kg/hour (max 1000 units/hour). PCI: 70-100 units/kg IV bolus (target ACT 250-300 s without GP IIb/IIIa, or 200-250 s with).
Route: Intravenous infusion (continuous) or IV bolus
Frequency: Continuous IV infusion; adjust per APTT
Max: Infusion titrated to APTT 1.5-2.5x control (therapeutic anticoagulation)
Indirect thrombin inhibitor via antithrombin III potentiation. Short half-life (1-2h) allows rapid reversal with protamine. APTT-guided dosing for therapeutic anticoagulation. ACT monitoring during PCI.

Paediatric dose

Dose: 75 units/kg
Route: IV bolus then infusion
Frequency: Initial bolus then 28 units/kg/hour (<1 year) or 20 units/kg/hour (>1 year)
Max: Per APTT-guided titration
BNFc for neonatal dosing. APTT-guided dose adjustment mandatory. Specialist haematology/cardiology input.

Dose adjustments

Renal

No dose adjustment required — but bleeding risk increases in renal impairment. Monitor APTT closely. LMWH preferred in CKD (more predictable).

Hepatic

Use with caution — reduced clotting factor synthesis increases baseline anticoagulation. Monitor APTT closely.

Paediatric weight-based calculator

BNFc for neonatal dosing. APTT-guided dose adjustment mandatory. Specialist haematology/cardiology input.

Clinical pearls

  • HIT (Heparin-Induced Thrombocytopenia Type 2): platelet fall >50% from baseline OR fall below 100 x10^9/L, typically days 5-14 of heparin therapy. Paradoxically causes THROMBOSIS (not bleeding). 4T score guides probability. Stop all heparin immediately — switch to argatroban or fondaparinux. DO NOT transfuse platelets.
  • APTT monitoring: target APTT 1.5-2.5x control (typically 60-100 seconds). Check APTT 6 hours after starting infusion and after each dose change. Use weight-based heparin nomogram.
  • ACT monitoring during PCI: activated clotting time (point-of-care) used intraoperatively — target 250-300 sec without GP IIb/IIIa inhibitor; 200-250 sec with. Measured in catheter lab every 30 minutes.
  • Protamine reversal: 1 mg protamine neutralises approximately 100 units UFH given in the preceding 2-3 hours. If >30 minutes since heparin — give 0.5 mg/mg. Maximum protamine dose 50 mg. Protamine allergy risk in patients with NPH insulin or fish allergy.
  • UFH vs LMWH in ACS: UFH preferred in STEMI requiring primary PCI (short half-life allows rapid reversal + ACT monitoring). LMWH (enoxaparin) preferred in NSTEMI managed conservatively.

Contraindications

  • Active bleeding
  • Haemophilia
  • Thrombocytopenia (HIT — heparin-induced thrombocytopenia)
  • Severe uncontrolled hypertension
  • Lumbar puncture within 24 hours

Side effects

  • Bleeding
  • Heparin-induced thrombocytopenia (HIT — type 1: non-immune, mild; type 2: immune-mediated, serious thrombosis)
  • Osteoporosis (prolonged use)
  • Hyperkalaemia (suppresses aldosterone)
  • Hypersensitivity reactions
  • Elevated transaminases (transient, benign)

Interactions

  • Antiplatelet drugs — additive bleeding risk
  • Warfarin/DOACs — additive; used in bridging protocols
  • Protamine — reversal agent (1 mg neutralises 100 units UFH given in past 2-3 hours)

Monitoring

  • APTT (6h after starting then every 6h until therapeutic, then daily)
  • Platelet count (daily for first 14 days — HIT monitoring)
  • Signs of bleeding
  • ACT (intraoperative PCI monitoring)

Reference: BNFc; BNF 90; ESC STEMI 2023; ESC NSTE-ACS 2020; BSH HIT Guidelines 2012; NICE NG185; SPC Heparin Sodium. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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