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# Magnesium Sulfate ## Overview Magnesium sulfate is an electrolyte and mineral supplement. It is available in oral and parenteral formulations. ## Primary Indications * Treatment of hypomagnesemia. * Prevention and treatment of seizures in preeclampsia and eclampsia. * Management of torsades de pointes. * Bronchodilator in severe asthma exacerbations (off-label, typically IV). * Antidote for certain calcium channel blocker and magnesium sulfate overdoses. ## Adult Dosing * **Hypomagnesemia:** * **IV:** 4 grams (40 mEq) administered as a loading dose over 15-30 minutes, followed by a maintenance infusion of 1-2 grams (10-20 mEq) per hour. Dosing may be adjusted based on serum magnesium levels and renal function. Maximum maintenance infusion rate is typically 2 grams/hour. * **IM:** 1-4 grams (10-40 mEq) every 4-6 hours as needed. * **Oral:** Doses vary widely depending on product strength and formulation (e.g., magnesium citrate, magnesium oxide). Consult specific product labeling. * **Preeclampsia/Eclampsia Prophylaxis and Treatment:** * **IV Loading Dose:** 4-6 grams (40-60 mEq) administered over 15-30 minutes. * **IV Maintenance Infusion:** 1-2 grams (10-20 mEq) per hour, adjusted to maintain deep tendon reflexes and adequate respiratory function. * **Torsades de Pointes:** 1-2 grams (10-20 mEq) diluted in 50-100 mL D5W infused over 5-10 minutes. May repeat as needed, followed by an infusion of 0.5-1 gram (5-10 mEq) per hour. ## Pediatric Dosing Dosing in pediatric patients is highly individualized and depends on the indication, serum magnesium levels, and renal function. Consult specialized pediatric critical care or toxicology resources for specific dosing recommendations. There is no single standard pediatric dose for many indications. ## 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 impairment unless absolutely necessary and with very close monitoring. ## Contraindications * Hypermagnesemia. * Hypersensitivity to magnesium sulfate. * Myocardial damage (generally). * Heart block (generally). ## Adverse Effects * **Common (IV):** Flushing, warmth, hypotension, nausea, vomiting, somnolence, decreased deep tendon reflexes. * **Serious:** Respiratory depression, cardiac arrest, hypermagnesemia (muscle weakness, lethargy, decreased reflexes, hypotension, bradycardia, ECG changes, respiratory paralysis, cardiac arrest). * **Oral:** Diarrhea, abdominal cramping. ## Key Drug Interactions * **Neuromuscular Blockers:** May potentiate neuromuscular blockade, leading to prolonged respiratory depression. * **Calcium Channel Blockers:** Additive hypotensive effects and potential for cardiac rhythm disturbances. * **Tetracyclines and Quinolones:** Magnesium can decrease the absorption of these antibiotics; administer at least 2 hours before or 4-6 hours after magnesium. * **Bisphosphonates:** Magnesium can decrease absorption; administer at least 2 hours before or 60 minutes after magnesium. ## Monitoring * **Parenteral Magnesium:** * Serum magnesium levels (especially with prolonged infusions or in renal impairment). * Deep tendon reflexes. * Respiratory rate and effort. * Blood pressure. * Urine output. * ECG (if concerns for cardiac effects). * **Oral Magnesium:** * Serum magnesium levels if diarrhea is severe or prolonged, or in patients with renal impairment. * Stool pattern for efficacy and tolerability. ## Clinical Pearls * When administered intravenously, magnesium sulfate should be infused slowly to minimize hypotension and flushing. * Rapid IV administration can lead to a paradoxical increase in blood pressure. * Assess for loss of deep tendon reflexes as an indicator of magnesium toxicity; reflexes typically disappear at serum magnesium levels around 8-12 mEq/L. * In cases of severe hypermagnesemia or magnesium sulfate overdose, discontinuation of magnesium and administration of IV calcium (e.g., calcium gluconate) may be indicated to antagonize cardiac and neuromuscular effects. * Oral magnesium salts can cause significant diarrhea, limiting their use for chronic supplementation in some individuals. Magnesium citrate is a potent osmotic laxative. *** *This information is intended for educational purposes only and does not substitute for professional medical advice. Always consult the most current prescribing information and local protocols before administering any medication.*