Magnesium Sulfate

• Eclampsia treatment & prophylaxis (severe pre-eclampsia)
• Fetal neuroprotection <30 weeks if delivery imminent
• Tocolysis (short-term, off-label)

NMDA receptor blockade + cerebral vasodilation → ↑ seizure threshold. Also reduces neuronal calcium influx.

• 4 g IV loading over 5–10 min
• 1 g/h infusion
• 2 g IV bolus for recurrent seizure
• 24 h after delivery or last seizure

Loading

4 g IV over 5–10 min

Maintenance

1 g/h IV for 24 h

Recurrent fit

2 g IV bolus

Therapeutic level

2–3.5 mmol/L

• AbsoluteMyasthenia gravis
• AbsoluteHeart block, severe renal failure (or halve dose + level monitoring)

• Flushing, warmth, nausea
• Loss of patellar reflexes (early toxicity)
• Respiratory depression (>5 mmol/L)
• Cardiac arrest (>7.5 mmol/L)

• • Reduces cerebral palsy risk by ~30% if given <30 weeks.
• • Neonatal hypotonia/respiratory depression possible — alert paediatrics.

• Nifedipine

  Caution

  Synergistic hypotension + neuromuscular block

• Calcium gluconate

  OK

  ANTIDOTE — 10 mL of 10% IV over 10 min

• Aminoglycosides

  Avoid

  Enhanced neuromuscular blockade

• 💡 Monitor RR, reflexes, urine output, SpO₂ hourly.
• 💡 Reduce infusion to 0.5 g/h if urine output <100 mL/4 h.
• 💡 Check Mg level if any toxicity sign.