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# Magnesium Sulfate ## Overview Magnesium sulfate is an essential mineral that plays a critical role in numerous physiological processes, including neuromuscular function, cardiac excitability, and enzyme activity. It is available for intravenous (IV) and intramuscular (IM) administration. ## Primary Indications * **Hypomagnesemia:** Treatment of magnesium deficiency. * **Eclampsia and Preeclampsia:** Prevention and treatment of seizures associated with severe preeclampsia and eclampsia. * **Torsades de Pointes:** Treatment of polymorphic ventricular tachycardia. * **Bronchospasm:** Adjunctive therapy for severe, life-threatening bronchospasm in asthma or COPD not responding to standard therapy. ## Adult Dosing * **Hypomagnesemia:** * **Severe deficiency:** Typically 4-5 grams (32-40 mEq) IV infused over 10-15 minutes, followed by a continuous infusion of 1-2 grams (8-16 mEq) per hour, or 1 gram (8 mEq) IM every 4-6 hours. Total daily dose rarely exceeds 30-40 grams (240-320 mEq). * **Milder deficiency:** Typically 1 gram (8 mEq) IM every 6-8 hours for 3-4 doses, or 5 grams (40 mEq) in 1 liter of IV fluid infused over 3 hours. * **Eclampsia/Preeclampsia:** Loading dose: 4-6 grams (32-48 mEq) IV infused over 5-10 minutes. Maintenance infusion: 1-2 grams (8-16 mEq) per hour. IM administration: 5 grams (40 mEq) IM in each buttock every 4 hours if IV access is not feasible. Maximum maintenance dose typically 15-20 grams (120-160 mEq) in 24 hours. * **Torsades de Pointes:** 1-2 grams (8-16 mEq) IV bolus over 5-10 minutes, followed by an infusion of 0.5-1 gram (4-8 mEq) per hour. Higher doses may be required. * **Bronchospasm:** 1-2 grams (8-16 mEq) IV infused over 15-20 minutes. ## Pediatric Dosing * **Hypomagnesemia:** Dosing varies widely based on severity and patient age/weight. Typical IV infusion for severe deficiency: 25-50 mg/kg (2-4 mEq/kg) over 10-15 minutes, followed by 20-30 mg/kg/day (1.6-2.4 mEq/kg/day) divided into 3-4 doses or as a continuous infusion. Max single dose typically 2 grams (16 mEq). * **Eclampsia/Preeclampsia:** Similar to adults, though specific pediatric guidelines are less common. * **Torsades de Pointes:** 25-50 mg/kg (2-4 mEq/kg) IV over 10 minutes, with a maximum single dose of 2 grams (16 mEq). Infusion can be repeated every 15-30 minutes if needed. Subsequent infusion: 10-15 mg/kg/hr (0.8-1.2 mEq/kg/hr). * **Bronchospasm:** 25-50 mg/kg (2-4 mEq/kg) IV infused over 15-30 minutes. Maximum dose typically 2 grams (16 mEq). ## Dose Adjustments Renal impairment: Magnesium is renally excreted. Reduce dose and monitor serum magnesium levels closely in patients with impaired renal function. Avoid in severe renal failure unless absolutely necessary and with caution. ## Contraindications * Hypermagnesemia. * Heart block. * Myocardial infarction (in the absence of torsades de pointes). * Hyperkalemia. * Severe renal impairment (absolute contraindication per some sources, relative contraindication per others). ## Adverse Effects * **Cardiovascular:** Hypotension, flushing, bradycardia, ECG changes, cardiac arrest. * **Neuromuscular:** Drowsiness, decreased deep tendon reflexes, muscle weakness, respiratory depression, coma. * **Gastrointestinal:** Nausea, vomiting, diarrhea (oral magnesium). * **Other:** Hyperthermia, sweating. ## Key Drug Interactions * **Neuromuscular Blockers (e.g., succinylcholine, vecuronium):** Magnesium can potentiate neuromuscular blockade, increasing the risk of respiratory depression and prolonged paralysis. * **Calcium Channel Blockers:** Additive hypotensive effects and potential for enhanced myocardial depression. * **Tetracyclines and Fluoroquinolones:** Magnesium can decrease the absorption of these antibiotics. Separate administration by at least 2 hours. * **Bisphosphonates:** Magnesium can decrease absorption. Separate administration. ## Monitoring * **Serum Magnesium Levels:** Monitor regularly, especially with IV infusions, in patients with renal impairment, or prolonged therapy. Therapeutic range for hypomagnesemia is typically 1.7-2.2 mEq/L (0.85-1.1 mmol/L). Levels above 4 mEq/L (2 mmol/L) can cause toxicity. * **Renal Function:** Assess baseline and monitor as clinically indicated. * **Deep Tendon Reflexes:** Monitor for loss of reflexes, which indicates hypermagnesemia. * **Respiratory Rate and Effort:** Monitor for signs of respiratory depression. * **ECG:** Monitor for cardiac rhythm changes. ## Clinical Pearls * Rapid IV infusion can cause hypotension and flushing. Infuse slowly as recommended. * In eclampsia, monitor for signs of magnesium toxicity, including absent reflexes, decreased respiratory rate, and altered mental status. Have calcium gluconate readily available as an antidote. * Magnesium sulfate is a potent vasodilator. Use with caution in patients with hypotension. * When treating hypomagnesemia, always correct potassium and phosphate levels if they are also low, as magnesium repletion can be impaired if these electrolytes are deficient. * The amount of elemental magnesium varies by salt form. For magnesium sulfate, there are approximately 8.1 mEq of elemental magnesium per gram of anhydrous magnesium sulfate. **Disclaimer:** This information is intended for healthcare professionals. Always verify current prescribing information and consult with a pharmacist or physician for patient-specific guidance.