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# Magnesium Sulfate ## Overview Magnesium sulfate is an essential mineral and electrolyte used for various medical conditions, including hypomagnesemia, preeclampsia/eclampsia, and torsades de pointes. It acts as a smooth muscle relaxant, CNS depressant, and is involved in numerous enzymatic reactions. ## Primary Indications * Treatment of hypomagnesemia. * Prevention and treatment of seizures in preeclampsia and eclampsia. * Treatment of torsades de pointes. * Management of status asthmaticus (adjunctive therapy). * Management of severe pre-operative anxiety (off-label in some settings). ## Adult Dosing * **Hypomagnesemia:** * **Severe (serum Mg < 1.3 mEq/L or < 0.65 mmol/L):** 4-6 grams (32-48 mEq or 16-24 mmol) IV over 1-2 hours, followed by 2-4 grams (16-32 mEq or 8-16 mmol) infused over the next 12-24 hours. Or, 1 gram (8 mEq or 4 mmol) IM every 6 hours for 4 doses. * **Less severe (serum Mg 1.3-1.7 mEq/L or 0.65-0.85 mmol/L):** 2-4 grams (16-32 mEq or 8-16 mmol) IV over 1-2 hours. * **Maintenance:** 1 gram (8 mEq or 4 mmol) IV or IM every 6-12 hours. * **Preeclampsia/Eclampsia Prophylaxis:** 4-5 grams (32-40 mEq or 16-20 mmol) IM in divided doses with 1-2 grams (8-16 mEq or 4-8 mmol) in each buttock, or 4-5 grams (32-40 mEq or 16-20 mmol) IV diluted in 100 mL IV fluid over 5 minutes. * **Preeclampsia/Eclampsia Treatment:** 4-5 grams (32-40 mEq or 16-20 mmol) IV bolus over 5-10 minutes, followed by a continuous infusion of 1-2 grams/hour (8-16 mEq/hr or 4-8 mmol/hr). **Local protocols may vary significantly for eclampsia treatment.** * **Torsades de Pointes:** 1-2 grams (8-16 mEq or 4-8 mmol) IV diluted in 10-20 mL of D5W given as a bolus over 5-10 minutes. This can be followed by a continuous infusion of 0.5-1 gram/hour (4-8 mEq/hr or 2-4 mmol/hr). * **Status Asthmaticus (Adjunctive):** 2 grams (16 mEq or 8 mmol) IV in 100 mL saline infused over 15-30 minutes. ## Pediatric Dosing * **Hypomagnesemia:** Dosing is highly variable and should be guided by serum magnesium levels and institutional protocols. Typical IV maintenance doses range from 0.05-0.2 mEq/kg/hr. A loading dose of 25-50 mg/kg (2-4 mEq/kg or 1-2 mmol/kg) IV over 4 hours has been used. * **Eclampsia:** Similar to adults, with dosing adjusted for weight and severity. Dosing may be based on 25-50 mg/kg per dose IV. **Consult pediatric critical care specialists.** * **Torsades de Pointes:** 25-50 mg/kg (2-4 mEq/kg or 1-2 mmol/kg) IV over 10-20 minutes. * **Status Asthmaticus:** 25-50 mg/kg (2-4 mEq/kg or 1-2 mmol/kg) IV in 100 mL IV fluid over 15-30 minutes. ## Dose Adjustments * **Renal Impairment:** Use with caution. Reduce dose and monitor serum magnesium levels closely. Patients with severe renal impairment may require significantly reduced doses or avoidance of magnesium sulfate. ## Contraindications * Hypermagnesemia. * Heart block. * Myocardial infarction (acute phase). * Hypertrophic obstructive cardiomyopathy. * Shock. ## Adverse Effects * **Common:** Flushing, sweating, nausea, vomiting, hypotension, somnolence, decreased deep tendon reflexes. * **Serious:** Respiratory depression, cardiac arrhythmias, cardiac arrest, coma, hypothermia. * **Local (IM):** Pain, swelling. * **IV Extravasation:** Tissue necrosis. ## Key Drug Interactions * **Nondepolarizing Neuromuscular Blockers:** Magnesium sulfate can potentiate neuromuscular blockade, leading to prolonged muscle weakness or respiratory paralysis. * **Calcium Salts:** May antagonize the cardiac and CNS effects of magnesium. * **Tetracyclines:** Oral magnesium may decrease absorption of tetracyclines. Separate administration by at least 2 hours. * **Bisphosphonates:** Oral magnesium may decrease absorption of bisphosphonates. Separate administration by at least 2 hours. ## Monitoring * **Serum Magnesium Levels:** Crucial, especially during IV infusions and in patients with renal impairment. Target levels vary by indication (e.g., 4-7 mEq/L or 2-3.5 mmol/L for eclampsia). * **Renal Function:** Monitor creatinine and urine output. * **Deep Tendon Reflexes:** Assess for presence and symmetry. Loss of reflexes is an early sign of hypermagnesemia. * **Respiratory Rate and Effort:** Monitor for signs of respiratory depression. * **Blood Pressure and Heart Rate:** Monitor for hypotension and arrhythmias. * **Urine Output:** Ensure adequate renal excretion. ## Clinical Pearls * Magnesium sulfate is administered as an anhydrous salt; therefore, calculations must account for the actual magnesium content (e.g., 1 gram of anhydrous magnesium sulfate contains approximately 8 mEq or 4 mmol of elemental magnesium). * When administered IV, magnesium sulfate must be diluted. Rapid IV administration can cause dangerous hypotension and cardiac arrhythmias. * Intramuscular administration is painful and should be given in divided doses in different muscle sites. * Toxicity is more likely in patients with impaired renal function. * Antidote for severe magnesium toxicity is IV calcium gluconate or calcium chloride. *** *Disclaimer: This information is intended for healthcare professionals. Always consult the most current prescribing information, institutional protocols, and relevant clinical guidelines before administering any medication.*