Magnesium Sulphate Injection: Indications and Uses
Magnesium sulphate injection is primarily indicated for the prevention and treatment of seizures in pre-eclampsia and eclampsia, as well as for replacement therapy in magnesium deficiency, especially in acute hypomagnesemia with tetany. 1
Primary Indications
1. Pre-eclampsia and Eclampsia Management
- Prevention of eclampsia in women with pre-eclampsia
- Treatment of eclamptic seizures in women who have already experienced convulsions
- Significantly more effective than phenytoin in preventing eclamptic seizures in hypertensive pregnant women 2
2. Magnesium Deficiency Treatment
- Replacement therapy in acute hypomagnesemia, especially when accompanied by tetany
- Used when serum magnesium levels fall below normal range (1.5 to 2.5 mEq/L) 1
- Can be added to total parenteral nutrition (TPN) to correct or prevent hypomagnesemia during therapy
Administration Protocols for Pre-eclampsia/Eclampsia
Intravenous Protocol (MAGPIE Trial)
- Loading dose: 4 g IV over 5-20 minutes
- Maintenance: 1-2 g/hour by controlled infusion pump 3, 4
- Target serum concentration: 1.8 to 3.0 mmol/L for treatment of eclamptic convulsions 4
Intramuscular Protocol (Pritchard Regimen)
- Loading dose: 4 g IV followed immediately by 5 g IM in each buttock (total 14 g)
- Maintenance: 5 g IM every 4 hours in alternating buttocks 3, 4
- Used when IV infusion pumps are not available or in resource-limited settings
Alternative Protocol (Serial IV Bolus)
- Loading dose: 6 g IV
- Maintenance: 2 g bolus every 2 hours 5
- Achieves comparable serum concentrations to continuous infusion
Task-Shifting Guidelines for Resource-Limited Settings
- Lower-level providers can initiate treatment with a loading dose and refer
- When only IM administration is possible, give 5 g MgSO4 in each buttock as loading dose before referral 3
- Better to initiate treatment with this dose than refer without any MgSO4 3
Duration of Treatment
- Continue for 24 hours postpartum in most cases
- Some evidence suggests that if at least 8 g of MgSO4 was given before delivery, continuing for 24 hours postpartum may not provide additional benefit 3
- However, ISSHP recommends continuing MgSO4 for 24 hours postpartum until further studies confirm findings in other populations 3
Monitoring and Safety
- Monitor deep tendon reflexes (loss occurs at 3.5-5 mmol/L)
- Monitor respiratory rate (respiratory paralysis occurs at 5-6.5 mmol/L)
- Monitor urine output (should maintain adequate renal function)
- Monitor serum magnesium concentrations when possible 4
- Cardiac conduction is altered at >7.5 mmol/L, and cardiac arrest can occur at >12.5 mmol/L 4
Neonatal Considerations
- Increasing maternal serum magnesium concentrations are associated with:
- Lower Apgar scores
- Increased need for intubation in delivery room
- Higher rates of admission to special care nursery
- Neonatal hypotonia 6
Clinical Pitfalls and Caveats
- Ensure clear protocols for MgSO4 use in each healthcare facility
- Use of MgSO4 for prevention and treatment of eclampsia varies widely and is often inconsistent with international guidelines 3
- Maternal toxicity is rare when properly administered and monitored 4
- In resource-limited settings, methyldopa and nifedipine are more readily available than other antihypertensives and can be used as first-line treatments alongside MgSO4 3
By following these evidence-based protocols for magnesium sulphate administration, healthcare providers can significantly reduce morbidity and mortality associated with pre-eclampsia and eclampsia while minimizing risks of toxicity.