What are the clinical uses of MgSO4 (magnesium sulfate)?

Clinical Uses of Magnesium Sulfate (MgSO4)

Primary Indications

Magnesium sulfate is indicated for three primary clinical uses: seizure prevention and control in severe preeclampsia/eclampsia, fetal neuroprotection in anticipated preterm delivery before 32 weeks gestation, and replacement therapy in magnesium deficiency states. 1, 2

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1. Severe Preeclampsia and Eclampsia

Seizure Prevention and Control

• MgSO4 is the most effective agent for preventing and controlling eclamptic seizures, with superior efficacy compared to phenytoin and diazepam. 1
• The drug should be administered to women with severe preeclampsia who have at least one clinical sign of seriousness to reduce the risk of eclampsia. 1
• Therapeutic serum magnesium levels of 1.8 to 3.0 mmol/L (approximately 4.3-7.2 mg/dL) are suggested for treatment of eclamptic convulsions, with optimal seizure control at 6 mg/100 mL. 2, 3

Standard Dosing Regimens

Intravenous Protocol:

• Loading dose: 4-6 grams IV over 20-30 minutes 4
• Maintenance: 1-2 grams per hour by continuous IV infusion 4
• Evidence suggests 2 grams per hour is more effective than 1 gram per hour, particularly in patients with BMI ≥25 kg/m². 4
• Continue for 24 hours postpartum in most cases. 4

Pritchard (IM) Protocol:

• Loading: 4 grams IV plus 10 grams IM (5 grams in each buttock) 4, 2
• Maintenance: 5 grams IM every 4 hours in alternate buttocks 4
• This regimen is particularly useful in resource-limited settings with limited IV access. 4

Critical Safety Monitoring

• Monitor deep tendon reflexes (loss occurs at 3.5-5 mmol/L), respiratory rate (≥12 breaths/minute required), and urine output (≥30 mL/hour). 1, 4, 3
• Never combine MgSO4 with calcium channel blockers (especially IV or sublingual nifedipine) as this can cause severe myocardial depression and hypotension. 1, 4
• Limit total fluid intake to 60-80 mL/hour to prevent pulmonary edema in preeclamptic patients with capillary leak. 4
• Serum magnesium levels should only be checked in specific high-risk situations including renal impairment, not routinely. 1

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2. Fetal Neuroprotection

Indication and Timing

• Administer MgSO4 when delivery of a potentially viable infant is anticipated before 32 weeks gestation to reduce the risk of cerebral palsy. 1
• MgSO4 reduces cerebral palsy risk by 32% (relative risk 0.68,95% CI 0.54-0.87) without increasing mortality (relative risk 1.04,95% CI 0.92-1.17) when administered before 30 weeks gestation. 1
• This indication is supported by 5 randomized controlled trials with enrollment starting as early as 24 weeks gestation. 1

Dosing for Neuroprotection

• Use low-dose protocols (between 4 g and 10.5 g total) to remain within the therapeutic window and avoid fetal toxicity. 5
• Higher doses used for tocolysis have been associated with toxicity to susceptible fetuses and lack of efficacy. 5

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3. Magnesium Deficiency States

Hypomagnesemia Treatment

• For mild magnesium deficiency: 1 gram (equivalent to 8.12 mEq) IM every 6 hours for four doses. 2
• For severe hypomagnesemia: Up to 250 mg (approximately 2 mEq) per kg body weight IM within 4 hours if necessary, or 5 grams (approximately 40 mEq) added to one liter of IV fluid for slow infusion over 3 hours. 2
• Caution must be observed to prevent exceeding renal excretory capacity during treatment of deficiency states. 2

Total Parenteral Nutrition (TPN)

• Maintenance requirements in adults range from 8 to 24 mEq (1 to 3 g) daily. 2
• For infants, the range is 2 to 10 mEq (0.25 to 1.25 g) daily. 2

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4. Other Clinical Uses

Barium Poisoning

• Usual dose: 1-2 grams IV to counteract muscle-stimulating effects. 2

Seizure Control (Non-Eclamptic)

• For seizures associated with epilepsy, glomerulonephritis, or hypothyroidism: 1 gram IM or IV. 2

Paroxysmal Atrial Tachycardia

• Use only if simpler measures have failed and there is no evidence of myocardial damage. 2
• Usual dose: 3-4 grams (30-40 mL of 10% solution) IV over 30 seconds with extreme caution. 2

Cerebral Edema Reduction

• 2.5 grams (25 mL of 10% solution) given IV. 2

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Toxicity Recognition and Management

Clinical Signs of Toxicity (by serum level)

• 2.5-5 mmol/L: ECG changes (prolonged PR, QRS, QT intervals) 6
• 3.5-5 mmol/L: Loss of patellar reflexes (first warning sign) 6, 3
• 4-5 mmol/L: Sedation, severe muscular weakness, respiratory depression 6
• 5-6.5 mmol/L: Respiratory paralysis 3
• 6-10 mmol/L: AV nodal block, bradycardia, hypotension 6
• >7.5 mmol/L: Altered cardiac conduction 3
• >12.5 mmol/L: Cardiac arrest 3

Emergency Treatment

• Immediately administer IV calcium as a physiological antagonist: calcium chloride 10% 5-10 mL or calcium gluconate 10% 15-30 mL IV over 2-5 minutes. 6
• Provide continuous cardiac monitoring for arrhythmias. 6
• Support blood pressure with vasopressors if hypotension persists despite calcium and fluid resuscitation. 6
• Correct other electrolyte abnormalities, particularly potassium. 6

High-Risk Populations

• Patients with renal impairment can develop toxicity after relatively lower doses; maximum dosage is 20 grams/48 hours with frequent serum magnesium monitoring. 6, 2
• Iatrogenic overdose is possible in pregnant women, particularly if oliguria develops—continuing administration when oliguria is present increases toxicity risk. 6

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Important Contraindications and Precautions

• Do not use MgSO4 continuously in pregnancy beyond 5-7 days as it can cause fetal abnormalities. 2
• Avoid NSAIDs for postpartum pain in preeclamptic patients as they worsen hypertension and increase acute kidney injury risk. 4
• MgSO4 may reduce antibiotic activity of streptomycin, tetracycline, and tobramycin when given together. 2
• A total daily dose of 30-40 grams should not be exceeded. 2