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Anticonvulsant / Neuroprotectant Pregnancy: Used in pregnancy (pre-eclampsia/eclampsia, neuroprotection) — standard of care

Magnesium Sulphate (Obstetric — Eclampsia/Neuroprotection)

Brand names: Magnesium Sulphate (generic)

Adult dose

Dose: Eclampsia (Magpie Trial): 4 g IV loading over 5 min, then 1 g/h infusion for 24h. Neuroprotection (preterm <34 weeks): 4 g IV loading over 20–30 min.
Route: IV
Frequency: Loading dose + maintenance infusion
Max: 4 g loading; 1–2 g/h maintenance
MAGPIE trial: MgSO4 halves risk of eclampsia and reduces maternal death. Monitor: respiratory rate ≥12/min, urine output ≥25 mL/h, patellar reflexes must be present before each bolus. Antidote: calcium gluconate 10 mL of 10% IV over 3 min.

Paediatric dose

Route: N/A
Frequency: N/A
Max: Neonatal neuroprotection context — mother receives drug
Concentration: 50% solution (dilute for IV use) N/A/ml
Fetal neuroprotection: maternal MgSO4 4g IV loading followed by 1g/h — given to mother when delivery <34 weeks to reduce cerebral palsy in neonate

Dose adjustments

Renal

Reduce infusion rate in renal impairment — magnesium accumulates; monitor levels

Hepatic

No dose adjustment required

Clinical pearls

  • Therapeutic magnesium level for eclampsia prevention: 2–3.5 mmol/L
  • Toxicity monitoring: check patellar reflexes before each dose — loss of reflexes is the first sign; stop infusion if absent
  • Antidote: calcium gluconate 10 mL of 10% IV over 3 min — should be at bedside
  • Neonatal effects: maternal MgSO4 causes neonatal hypotonia and respiratory depression — neonatal team should be aware

Contraindications

  • Heart block or myasthenia gravis (significant risk of neuromuscular blockade)
  • Anuria

Side effects

  • Flushing
  • Sweating
  • Hypotension
  • Nausea
  • Loss of deep tendon reflexes (first sign of toxicity)
  • Respiratory depression (toxicity)
  • Cardiac arrest (severe toxicity)

Interactions

  • Calcium channel blockers — enhanced neuromuscular blockade; profound hypotension risk (nifedipine combination requires close monitoring)
  • Non-depolarising NMBAs — enhanced blockade

Monitoring

  • Respiratory rate (>12/min mandatory)
  • Urine output (>25 mL/h)
  • Patellar reflexes (absent = toxicity)
  • Serum magnesium levels (if renal impairment)
  • Serum calcium (if prolonged infusion)

Reference: BNFc; BNF; MAGPIE Trial (Magpie Trial Collaboration Group, Lancet 2002); RCOG Green-top 10a (Eclampsia). Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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