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# Magnesium Sulfate ## Overview Magnesium sulfate is an electrolyte. It is an essential mineral involved in numerous physiological processes, including nerve impulse transmission, muscle contraction, and cardiac function. ## Primary Indications * Treatment of hypomagnesemia. * Prevention and treatment of seizures in preeclampsia and eclampsia. * Management of torsades de pointes. * Management of severe bronchospasm in asthma refractory to standard therapy. ## Adult Dosing * **Hypomagnesemia:** * **Severe symptomatic (e.g., seizures, arrhythmias):** 4-5 g (32-40 mEq) IV infused over 5-20 minutes. Subsequent doses may be given every 4 hours as needed or as a continuous infusion. * **Asymptomatic:** 1-2 g (8-16 mEq) IV infused over 1 hour, followed by 1 g (8 mEq) every 8 hours for 4 doses or a continuous infusion. * **Preeclampsia/Eclampsia:** 4-5 g (32-40 mEq) IV infused over 5-20 minutes, followed by a continuous infusion of 1-2 g/hour. Loading dose may be repeated if seizure occurs. * **Torsades de Pointes:** 1-2 g (8-16 mEq) IV infused rapidly (e.g., over 5 minutes), followed by 0.5-1 g/hour infusion. * **Severe Bronchospasm:** 1-2 g (8-16 mEq) IV infused over 15-30 minutes. *Note: Dosing for hypomagnesemia can also be based on serum magnesium levels and weight-based calculations, often determined by local protocol.* ## Pediatric Dosing * **Hypomagnesemia:** Dosing is highly variable and often determined by local protocol and serum magnesium levels. General guidelines include: * **Severe:** 25-50 mg/kg/dose (2-4 mEq/kg/dose) IV infused over 30-60 minutes. May repeat every 4-12 hours. * **Continuous infusion:** 0.05-0.25 mEq/kg/hour (or 3-15 mg/kg/hour). * **Eclampsia:** 40 mg/kg (3.2 mEq/kg) IV infused over 5-10 minutes, followed by a continuous infusion of 20 mg/kg/hour (1.6 mEq/kg/hour). Maximum loading dose is typically 2 g. ## Dose Adjustments * **Renal Impairment:** Magnesium is renally excreted. Use with caution in patients with impaired renal function. Monitor serum magnesium levels closely. Dose reduction or discontinuation may be necessary. ## Contraindications * Hypermagnesemia. * Heart block (except in the context of torsades de pointes). * Myocardial infarction (unless to treat torsades de pointes). * Hypotension. * Shock. * Severe renal failure. ## Adverse Effects * **Common:** Flushing, sweating, hypotension, nausea, vomiting, decreased deep tendon reflexes, somnolence, respiratory depression. * **Serious:** Cardiac arrhythmias, cardiac arrest, respiratory arrest, hypermagnesemia. ## Key Drug Interactions * **Neuromuscular Blocking Agents:** May potentiate neuromuscular blockade, leading to prolonged muscle weakness or respiratory depression. * **Calcium Channel Blockers:** Additive hypotensive effects. * **Tetracyclines and Bisphosphonates:** Magnesium can decrease the absorption of these medications. Administer at least 2 hours before or 4-6 hours after. ## Monitoring * **Serum magnesium levels:** Monitor frequently, especially with continuous infusions or in patients with renal impairment. Therapeutic levels for hypomagnesemia are typically 2-3.5 mEq/L. Levels above 4 mEq/L warrant caution, and levels above 7 mEq/L are associated with severe toxicity. * **Renal function:** Assess baseline and monitor periodically. * **Deep tendon reflexes:** Assess for loss of reflexes, which can indicate magnesium toxicity. * **Respiratory rate and effort:** Monitor for signs of respiratory depression. * **Blood pressure and heart rate:** Monitor for hypotension and cardiac arrhythmias. * **Urine output:** Monitor for adequacy of renal function. ## Clinical Pearls * Magnesium sulfate is a potent medication. Administer IV infusions slowly to avoid hypotension and other adverse effects. * In cases of severe symptomatic hypomagnesemia or eclampsia, rapid IV infusion may be indicated, but requires close monitoring. * Calcium gluconate or calcium chloride is the antidote for magnesium toxicity and should be readily available. * Intramuscular administration can be painful and is typically reserved for situations where IV access is not feasible. *** *Disclaimer: This information is for educational purposes only and does not constitute medical advice. Always consult with a qualified healthcare professional and refer to the most current prescribing information for definitive guidance.*