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Anticoagulant — VTE Prophylaxis (UFH) Pregnancy: Compatible — does not cross placenta; standard anticoagulant in pregnancy with renal failure

Heparin Unfractionated (Prophylaxis)

Brand names: Heparin Sodium (generic)

Adult dose

Dose: VTE prophylaxis (moderate risk): 5000 units SC BD–TDS. Treatment (not prophylaxis): loading 5000 units IV followed by infusion titrated to APTT ratio 1.5–2.5.
Route: Subcutaneous (prophylaxis) or IV (treatment)
Frequency: BD–TDS (prophylaxis SC)
Max: 5000 units per SC dose for prophylaxis
Preferred over LMWH in renal failure (eGFR <30) as it is not renally cleared. Stop 4h before spinal/epidural. Restart 1h after needle removal.

Paediatric dose

Dose: 75 units/kg
Route: IV loading then infusion
Frequency: Loading then 20 units/kg/h, titrate to APTT
Max: 5000 units loading; titrate infusion
Concentration: 1000 units/mL or 5000 units/mL units/ml
Paediatric VTE treatment: 75 units/kg loading IV over 10 min, then 20 units/kg/h (infants <1 year: 28 units/kg/h). Monitor APTT 4h after start; target APTT ratio 1.5–2.5.

Dose adjustments

Renal

No dose adjustment required — preferred over LMWH in severe renal impairment

Hepatic

Caution in severe hepatic impairment (anticoagulant effect unpredictable)

Paediatric weight-based calculator

Paediatric VTE treatment: 75 units/kg loading IV over 10 min, then 20 units/kg/h (infants <1 year: 28 units/kg/h). Monitor APTT 4h after start; target APTT ratio 1.5–2.5.

Clinical pearls

  • HIT: check platelet count at day 5–7 of any heparin course; >50% drop in platelets is a red flag — stop heparin immediately, use alternative anticoagulant
  • APTT monitoring required for treatment doses — take sample 4h after starting infusion or dose change
  • Spinal/epidural: UFH must be stopped 4h before, not started for 1h after needle placement (per ASRA guidelines)
  • Antidote: protamine sulphate 1 mg neutralises 100 units of heparin (max 50 mg protamine per dose)

Contraindications

  • Active major bleeding
  • HIT (current — use alternative anticoagulant)
  • Thrombocytopenia <50×10⁹/L

Side effects

  • Bleeding
  • HIT (thrombocytopenia + thrombosis — 0.5–3%)
  • Osteoporosis (prolonged use)
  • Hyperkalaemia (aldosterone suppression)
  • Hypersensitivity

Interactions

  • Anticoagulants — additive bleeding
  • NSAIDs/aspirin — increased bleeding risk

Monitoring

  • APTT (treatment doses)
  • Platelet count (baseline, day 5–7, and if clinical concern)
  • Potassium
  • Signs of bleeding

Reference: BNFc; BNF; ASRA Guidelines; NICE NG89; BCSH Heparin Guidelines. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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