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Anticoagulant (parenteral) Pregnancy: Safe in pregnancy (does not cross placenta); preferred anticoagulant near delivery.

Unfractionated Heparin (UFH)

Brand names: Heparin Sodium

Adult dose

Dose: IV: loading 5000 units bolus; infusion 18 units/kg/hour adjusted by APTT
Route: IV infusion or SC (prophylaxis)
Frequency: Continuous IV infusion; APTT 6 hourly until stable then 12–24 hourly
Max: Adjusted by APTT ratio (target 1.5–2.5)
Treatment (VTE/ACS): 5000 units IV bolus, then infusion per weight-based nomogram. Prophylaxis: 5000 units SC every 8–12 hours. APTT target 1.5–2.5× control. Reverse with protamine sulfate 1 mg per 100 units heparin given in last 2 hours.

Paediatric dose

Dose: 75 units/kg
Route: IV
Frequency: Continuous infusion
Max: 5000 units bolus
Concentration: 1000 units/ml
Loading: 75 units/kg IV over 10 min. Maintenance: neonates 28 units/kg/hour; infants <1 year 28 units/kg/hour; children >1 year 20 units/kg/hour. Adjust by anti-Xa level.

Dose adjustments

Renal

Caution in severe renal impairment (increased bleeding risk); no dose adjustment for APTT-guided therapy.

Hepatic

Use with caution; monitor carefully.

Paediatric weight-based calculator

Loading: 75 units/kg IV over 10 min. Maintenance: neonates 28 units/kg/hour; infants <1 year 28 units/kg/hour; children >1 year 20 units/kg/hour. Adjust by anti-Xa level.

Clinical pearls

  • Monitor platelet count from day 4 onwards (HIT risk) — 4Ts score
  • If HIT suspected: stop ALL heparin and switch to argatroban or danaparoid
  • UFH preferred over LMWH in renal failure (reversible with protamine)
  • Use 1000 units/mL concentration for infusion (standardise to reduce errors)
  • Therapeutic range: anti-Xa 0.3–0.7 IU/mL or APTT 1.5–2.5×

Contraindications

  • Active major bleeding
  • Haemophilia and other haemorrhagic disorders
  • Thrombocytopenia (platelet count <60,000)
  • History of HIT (Heparin-Induced Thrombocytopenia)

Side effects

  • Bleeding
  • HIT Type II (immune-mediated — life-threatening; reduce platelet count >50% typically 5–10 days after start)
  • Osteoporosis (prolonged use)
  • Hyperkalaemia
  • Hypersensitivity
  • Transient alopecia

Interactions

  • Antiplatelet drugs — increased bleeding risk
  • NSAIDs — increased bleeding risk
  • Protamine — reversal (1 mg per 100 units given in last 2 hours)

Monitoring

  • APTT (every 6h until stable, then 12–24h)
  • Platelet count daily (days 4–14)
  • Anti-Xa levels (alternative)
  • Signs of bleeding

Reference: BNFc; BNF; BCSH Guidelines; NICE NG158. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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