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# Magnesium Sulfate ## Overview Magnesium sulfate is an essential mineral that plays a crucial role in various biochemical reactions. It is available in injectable and oral forms. ## 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 (adjunctive therapy). ## Adult Dosing * **Hypomagnesemia:** * **Severe (serum magnesium < 1.5 mEq/L):** 4-5 g (32-40 mEq) IV infused over 3-5 minutes, followed by 1-2 g (8-16 mEq) per hour as a continuous infusion. Dosing may be adjusted based on serum magnesium levels and clinical response. * **Less Severe (serum magnesium 1.5-2.5 mEq/L):** 1-2 g (8-16 mEq) IV infused over 5-10 minutes. * **Oral supplementation:** 3-6 g (24-48 mEq) daily divided into 3-4 doses. * **Preeclampsia/Eclampsia prophylaxis:** 4 g IV loading dose over 15-20 minutes, followed by 1-2 g per hour as a continuous infusion. * **Preeclampsia/Eclampsia treatment (seizures):** 4-5 g (32-40 mEq) IV infused over 5 minutes. Follow with 5 g (40 mEq) IM into each buttock, or a continuous IV infusion of 1-2 g per hour. Infusion rates and duration depend on clinical response and magnesium levels. * **Torsades de pointes:** 1-2 g (8-16 mEq) IV, often in 100 mL D5W, infused over 5-10 minutes. May be repeated. Further doses can be given as a continuous infusion of 0.5-1 g/hour. * **Severe asthma:** 2 g IV infused over 15-20 minutes. ## Pediatric Dosing * **Hypomagnesemia:** Dosing varies widely based on age, weight, and severity. A common initial dose is 25-50 mg/kg (0.2-0.4 mEq/kg) IV over 10 minutes, followed by an infusion of 10-30 mg/kg/hour (0.08-0.24 mEq/kg/hour). **Consult specific pediatric guidelines or protocols for precise dosing.** * **Preeclampsia/Eclampsia (off-label in some pediatric cases):** Dosing is highly individualized and based on weight and clinical situation. **Consult pediatric critical care or obstetrics guidelines.** * **Torsades de pointes:** 25-50 mg/kg (0.2-0.4 mEq/kg) IV over 10-20 minutes. Maximum dose typically 2 g. May repeat. ## Dose Adjustments * **Renal Impairment:** Magnesium is renally excreted. Use with caution in patients with impaired renal function. Reduce dose and monitor serum magnesium levels closely. In severe renal impairment, avoid parenteral magnesium if possible. * **Hepatic Impairment:** No specific dose adjustment is usually needed, but monitor closely as hepatic encephalopathy can sometimes be associated with electrolyte imbalances. ## Contraindications * Hypermagnesemia. * Heart block. * Myocardial infarction. * A-V conduction abnormalities. * Hypersensitivity to magnesium sulfate. ## Adverse Effects * **Common:** Flushing, sweating, hypotension, nausea, vomiting, decreased deep tendon reflexes, somnolence, muscle weakness. * **Serious:** Respiratory depression, cardiac arrhythmias, cardiac arrest, loss of deep tendon reflexes, paralysis, hypermagnesemia (especially in renal impairment). ## Key Drug Interactions * **Neuromuscular blocking agents (e.g., succinylcholine, rocuronium):** Magnesium can potentiate neuromuscular blockade, increasing the risk of prolonged respiratory depression. * **Calcium:** Calcium may antagonize some of the cardiac and CNS effects of magnesium. * **Tetracyclines and bisphosphonates:** Oral magnesium can decrease the absorption of these agents. Administer oral magnesium at least 2 hours before or 4-6 hours after these medications. ## Monitoring * **Serum magnesium levels:** Frequency depends on the indication and route of administration, typically every 4-6 hours initially for IV infusions, then as clinically indicated. Therapeutic range for hypomagnesemia is generally 1.7-2.6 mEq/L (0.7-1.05 mmol/L). For seizure prophylaxis/treatment, target range is often 4-7 mEq/L (1.6-2.8 mmol/L). * **Renal function:** Monitor creatinine and BUN. * **Deep tendon reflexes:** Assess for loss of reflexes, which can indicate hypermagnesemia. * **Respiratory rate and effort:** Monitor for signs of respiratory depression. * **Blood pressure and heart rate:** Monitor for hypotension and arrhythmias. * **Urine output:** Adequate urine output is crucial for magnesium excretion. ## Clinical Pearls * Intravenous magnesium sulfate should be administered slowly to avoid hypotension and flushing. * Monitor closely for signs of magnesium toxicity, especially in patients with impaired renal function. The antidote for severe magnesium toxicity is intravenous calcium (e.g., calcium gluconate). * When treating hypomagnesemia, oral supplementation is preferred for long-term maintenance if the patient can tolerate it and has adequate GI absorption. * In preeclampsia/eclampsia, continuous monitoring of reflexes, respiratory rate, and urine output is essential. *** *This information is intended for healthcare professionals. It is essential to consult the most current prescribing information, institutional protocols, and relevant literature for definitive guidance. Dosing may vary based on specific patient factors and clinical context.*