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Anticoagulant — ACS / PE / Thrombus Pregnancy: Safe in pregnancy — does not cross placenta; preferred anticoagulant in pregnancy

Unfractionated Heparin (IV)

Brand names: Heparin Sodium

Adult dose

Dose: 5000 units IV bolus, then 1000-2000 units/hr IV infusion titrated to APTT ratio 1.5-2.5
Route: Intravenous bolus + continuous infusion
Frequency: Continuous infusion
Max: Titrated to APTT; use weight-based nomogram
STEMI (not undergoing PCI): 60 units/kg bolus (max 4000 units), then 12 units/kg/hr. Massive PE: 80 units/kg bolus then 18 units/kg/hr. Use heparin nomogram for titration. Protamine antidote available

Paediatric dose

Dose: 75 units/kg IV bolus over 10 min; then 28 units/kg/hr (under 1 year); 20 units/kg/hr (over 1 year) units/kg
Route: IV
Frequency: Continuous infusion
Max: Titrated to anti-Xa or APTT
Seek specialist haematology input for paediatric anticoagulation

Dose adjustments

Renal

No dose adjustment; however renal impairment increases bleeding risk — monitor more closely

Hepatic

Use with caution — impaired synthesis of coagulation factors increases bleeding risk

Paediatric weight-based calculator

Seek specialist haematology input for paediatric anticoagulation

Clinical pearls

  • Antidote: protamine sulfate — 1 mg neutralises approximately 100 units heparin; give slowly IV (max 50 mg over 10 min); risk of anaphylaxis (especially in fish-allergy or prior protamine exposure)
  • HIT: suspect if platelets fall by more than 50% between days 5-14 — use 4Ts score; stop heparin immediately and switch to argatroban or fondaparinux; NEVER give warfarin until platelets recover above 150
  • IV heparin preferred over LMWH in acute settings requiring rapid reversal (PCI, surgery, bleeding risk) — shorter half-life and protamine reversal are key advantages
  • APTT monitoring: therapeutic range is APTT ratio 1.5-2.5; check 6 hours after bolus, then 6 hours after each dose change, then daily when stable
  • Anti-Xa monitoring preferred in obesity (BMI above 40), pregnancy, or renal impairment — APTT unreliable in these groups

Contraindications

  • Active major bleeding
  • HIT (heparin-induced thrombocytopenia)
  • Haemorrhagic stroke
  • Severe thrombocytopenia (platelets under 80)

Side effects

  • Bleeding (most common)
  • HIT (immune-mediated — platelet fall day 5-14; paradoxical thrombosis)
  • Hyperkalaemia (aldosterone suppression)
  • Osteoporosis (prolonged use)
  • Transaminase elevation

Interactions

  • Antiplatelet agents (increased bleeding risk)
  • NSAIDs (increased bleeding)
  • Other anticoagulants (additive)

Monitoring

  • APTT ratio (or anti-Xa) every 6 hours until stable, then daily
  • Platelet count (daily from day 4-14 — HIT surveillance)
  • Signs of bleeding
  • Potassium (aldosterone suppression)

Reference: BNFc; BNF 90; NICE NG185 (ACS); NICE NG158 (VTE); BSH HIT Guidelines 2012; Anticoagulation UK. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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