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# Magnesium Sulfate ## Overview Magnesium sulfate is an essential mineral used to treat and prevent hypomagnesemia and for its tocolytic, anticonvulsant, and bronchodilator properties. It is available in oral and intravenous (IV) formulations. ## Primary Indications * Treatment of hypomagnesemia. * Prevention of hypomagnesemia in specific patient populations (e.g., alcohol use disorder, malabsorption syndromes). * Management of preeclampsia and eclampsia. * Tocolysis to inhibit preterm labor. * Adjunctive therapy in severe asthma exacerbations. ## Adult Dosing * **Hypomagnesemia:** * **Severe (serum magnesium < 1.0 mEq/L):** 4-6 grams IV initially, followed by 1-2 grams/hour as a continuous infusion or 1 gram every 4-6 hours. Total daily dose should not exceed 30 grams without careful monitoring. * **Less severe (serum magnesium 1.0-1.5 mEq/L):** 1-2 grams IV in divided doses over 12-24 hours. * **Oral repletion:** 3-4 grams (30-40 mEq) orally daily in divided doses, titrating to achieve serum magnesium levels. Max oral dose typically 50 mEq/day. * **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 plus 5 grams IV. * **Tocolysis:** 4-6 grams IV loading dose, followed by 2 grams/hour IV infusion. Dosing may vary significantly by institutional protocol. * **Asthma exacerbation:** 1-2 grams IV in 50-100 mL NS over 15-30 minutes. ## Pediatric Dosing Dosing for pediatric patients is highly variable and often based on weight and indication. Consult specialized pediatric resources for specific dosing recommendations. * **Hypomagnesemia (Severe):** 25-50 mg/kg IV over 3-6 hours. Maximum dose often 2 grams. * **Eclampsia (Adjunctive):** Similar to adults, but adjusted for weight. Dosing varies widely by protocol. ## Dose Adjustments * **Renal Impairment:** Magnesium is renally excreted. In patients with impaired renal function, reduce the dose and monitor serum magnesium levels closely. Avoid IV magnesium in severe renal failure. Oral magnesium may be continued cautiously with monitoring. ## Contraindications * Hypermagnesemia. * Heart block. * Myocardial infarction. * Severe renal impairment (especially for IV administration). * Intestinal obstruction or perforation (for oral administration). ## Adverse Effects * **Common:** Flushing, warmth, sweating, hypotension, nausea, vomiting, diarrhea (oral). * **Serious:** Respiratory depression, loss of deep tendon reflexes, altered mental status, bradycardia, cardiac arrest, hypermagnesemia (especially with renal impairment). ## Key Drug Interactions * **Neuromuscular blockers (e.g., succinylcholine, vecuronium):** Magnesium can potentiate neuromuscular blockade, increasing the risk of prolonged muscle weakness and respiratory depression. * **Calcium channel blockers:** Additive hypotensive effects. * **Antibiotics (tetracyclines, fluoroquinolones):** Magnesium can decrease the absorption of oral tetracyclines and fluoroquinolones. Separate administration by at least 2-4 hours. ## Monitoring * **Serum magnesium levels:** Especially with IV therapy or in renal impairment. Target levels vary by indication (e.g., 2.1-3.7 mEq/L for preeclampsia, 2.5-4.0 mEq/L for hypomagnesemia). * **Renal function (BUN, creatinine).** * **Deep tendon reflexes:** Loss of reflexes indicates magnesium toxicity. * **Respiratory rate and depth.** * **Blood pressure and heart rate.** * **Urine output.** * **ECG:** For signs of cardiotoxicity. ## Clinical Pearls * IV magnesium sulfate should be administered slowly and with continuous monitoring, especially in patients with cardiac or renal compromise. * The 50% injectable solution contains 4.07 mEq of elemental magnesium per gram of magnesium sulfate. * Hypocalcemia may coexist with hypomagnesemia; correction of magnesium may unmask or worsen hypocalcemia. * Antidote for magnesium toxicity is IV calcium (e.g., calcium gluconate). *** **Disclaimer:** This information is intended for healthcare professionals. Always consult the most current prescribing information, institutional protocols, and patient-specific factors before administering any medication.