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# Magnesium Sulfate ## Overview Magnesium sulfate is an essential mineral. It plays a role in numerous biochemical reactions, including energy production, nucleic acid and protein synthesis, neuromuscular transmission, and muscle contraction. ## Primary Indications * Treatment of hypomagnesemia. * Prevention and treatment of seizures in severe preeclampsia and eclampsia. * Management of torsades de pointes. * Treatment of status asthmaticus. * Management of acute myocardial infarction (off-label, though some guidelines recommend it). ## Adult Dosing * **Hypomagnesemia:** * **Severe/Symptomatic:** 4-6 grams IV initially, followed by 1-2 grams/hour IV infusion. Daily maintenance dose typically 20-40 grams IV. * **Mild/Asymptomatic:** 1 gram IV every 6 hours for 4 doses, or 1 gram IM every 6 hours for 4 doses. * **Preeclampsia/Eclampsia:** Loading dose: 4-6 grams IV over 5-20 minutes. Maintenance infusion: 1-2 grams/hour IV. An alternative is 5 grams IM into each buttock. * **Torsades de Pointes:** 1-2 grams IV in 50-100 mL D5W over 5-10 minutes. Repeat doses may be administered if indicated. * **Status Asthmaticus:** 2 grams IV diluted in 50 mL normal saline infused over 15-20 minutes. Dosing may vary based on local protocol and electrolyte levels. ## Pediatric Dosing * **Hypomagnesemia:** 25-50 mg/kg/dose IV infused over 1-4 hours. Maximum dose 2 grams. Repeat every 6-12 hours as needed. * **Status Asthmaticus:** 25-40 mg/kg IV infused over 15-30 minutes. Maximum dose 2 grams. * **Preeclampsia/Eclampsia:** Not typically used in pediatric patients unless specifically indicated and managed by specialists. Dosing requires careful titration and monitoring. ## Dose Adjustments * **Renal Impairment:** Magnesium is renally excreted. In patients with impaired renal function, doses should be reduced and serum magnesium levels closely monitored to prevent accumulation and toxicity. Caution with CrCl < 30 mL/min. ## Contraindications * Hypermagnesemia. * Heart block. * Myocardial infarction (relative contraindication in some cases, assess risk/benefit). * Shock. * Digitalis toxicity. * Severe renal impairment. ## Adverse Effects * **Common:** Flushing, sweating, warmth, hypotension, nausea, vomiting, drowsiness, decreased deep tendon reflexes. * **Serious:** Respiratory depression, cardiac arrhythmias, cardiac arrest, loss of deep tendon reflexes, coma, hypermagnesemia. ## Key Drug Interactions * **Calcium Salts:** May antagonize neuromuscular and cardiac effects of magnesium. * **Neuromuscular Blockers (e.g., succinylcholine, rocuronium):** Magnesium can potentiate neuromuscular blockade, increasing the risk of prolonged paralysis and respiratory depression. * **Nifedipine:** Concomitant use may lead to profound hypotension. * **Tetracyclines and Bisphosphonates:** IV magnesium can decrease the absorption of these drugs; separate administration by at least 2-3 hours. ## Monitoring * **Serum Magnesium Levels:** Regularly monitor, especially during prolonged infusions or in patients with renal impairment. Therapeutic range for hypomagnesemia is typically 1.7-2.2 mmol/L (4-5.5 mg/dL), but may be higher for specific indications (e.g., preeclampsia). Toxicity may occur above 4 mmol/L (10 mg/dL). * **Renal Function:** Monitor creatinine and BUN. * **Deep Tendon Reflexes:** Assess for depression or loss, an early sign of toxicity. * **Respiratory Rate and Depth:** Monitor for signs of respiratory depression. * **Electrocardiogram (ECG):** Monitor for QT interval prolongation or other arrhythmias, particularly in patients at risk. * **Blood Pressure:** Monitor for hypotension. ## Clinical Pearls * Magnesium sulfate is a CNS depressant and vasodilator. * Rapid IV infusion can cause hypotension, flushing, and cardiac arrhythmias. Always dilute and infuse as recommended. * IV calcium gluconate or calcium chloride is the antidote for magnesium toxicity. * In preeclampsia, magnesium is given to prevent seizures, not to treat hypertension. * Magnesium sulfate precipitates with calcium and phosphate. Do not mix in the same IV line. *** *This information is intended for healthcare professionals and does not replace current prescribing information. Always consult the official drug monograph and institutional protocols for the most up-to-date and comprehensive guidance.*