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Anticoagulant Pregnancy: B — drug of choice for anticoagulation in pregnancy (does not cross placenta)

Enoxaparin (LMWH)

Brand names: Clexane, Lovenox

Adult dose

Dose: VTE treatment: 1.5mg/kg SC OD or 1mg/kg SC BD. VTE prophylaxis: 20–40mg SC OD. ACS: 1mg/kg SC BD
Route: Subcutaneous (SC) / IV (loading in ACS)
Frequency: Once or twice daily depending on indication
Max: Therapeutic: 180mg/day. Prophylaxis: 40mg/day (standard risk)
VTE treatment: 1mg/kg BD if BMI >40 or BMI <18. High VTE risk (surgical): 40mg OD. Enoxaparin in CKD: reduce to 0.5–0.75mg/kg BD if GFR <30. In pregnancy: weight-adjusted BD dosing throughout — check anti-Xa levels.

Paediatric dose

Dose: 1 mg/kg
Route: SC
Frequency: Twice daily (therapeutic)
Max: 100mg
Concentration: 100 mg/ml

Dose adjustments

Renal

GFR <30: reduce to 1mg/kg OD (treatment) or 20mg OD (prophylaxis). Monitor anti-Xa levels. Use UFH if GFR <15.

Paediatric weight-based calculator

Clinical pearls

  • Anti-Xa monitoring required in: obesity (BMI >40), extremes of weight (<50kg, >120kg), pregnancy, and renal impairment.
  • Therapeutic anti-Xa range: BD dosing 0.6–1.0 IU/ml at 4h post-dose. OD dosing: 1.0–2.0 IU/ml at 4h.
  • Hold enoxaparin 12h before neuraxial anaesthesia (prophylactic dose) or 24h (therapeutic dose).
  • Partial reversal with protamine: 1mg protamine reverses ~1mg enoxaparin (only partially effective — ~60–80%).
  • Switch to UFH infusion for patients likely to need surgery within hours (shorter half-life, fully reversible).

Contraindications

  • Active major haemorrhage
  • HIT (heparin-induced thrombocytopaenia) — use argatroban or fondaparinux instead
  • Spinal anaesthesia / lumbar puncture within 12h (prophylaxis) or 24h (treatment) — timing guidance
  • Severe uncontrolled hypertension

Side effects

  • Bleeding
  • Injection site bruising and haematoma
  • Heparin-induced thrombocytopaenia (HIT) — lower risk than UFH (~0.1%)
  • Osteoporosis (rare — with prolonged use)

Interactions

  • NSAIDs / aspirin: additive bleeding risk
  • Anticoagulants: additive effect
  • Nitrates: may reduce anticoagulant effect (theoretical)

Monitoring

  • Platelet count (at baseline
  • day 5–7
  • day 14 if prolonged)
  • anti-Xa in special populations
  • Hb

Reference: BNFc; NICE NG158 VTE Prevention; BTS PE Guidelines 2023; NICE BNF 84. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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