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# Magnesium Sulfate ## Overview Magnesium sulfate is an essential mineral that plays a critical role in numerous enzymatic reactions, neuromuscular transmission, and myocardial function. It is available in intravenous and intramuscular formulations. ## Primary Indications * Treatment of hypomagnesemia. * Prevention and treatment of seizures in preeclampsia and eclampsia. * Management of torsades de pointes. * Treatment of severe bronchospasm (e.g., status asthmaticus). ## Adult Dosing **Hypomagnesemia:** * **Severe (<1 mg/dL):** 4-6 grams IV infused over 3-4 hours, followed by a maintenance infusion of 1-2 grams per hour. Max infusion rate generally 1 gram/hour. * **Less Severe:** 1-4 grams IV or IM every 4-6 hours as needed. * **Maintenance:** 4-6 grams IV infused over 24 hours. **Preeclampsia/Eclampsia:** * **Loading Dose:** 4-6 grams IV infused over 15-20 minutes. * **Maintenance Dose:** 1-2 grams per hour IV infusion. Adjustments based on seizure activity and magnesium levels. **Torsades de Pointes:** * **Acute:** 1-2 grams IV bolus, followed by a continuous infusion of 0.5-1 gram per hour. **Severe Bronchospasm:** * 1-2 grams IV infused over 15-30 minutes. ## Pediatric Dosing Dosing in pediatrics is complex and often based on local protocols, weight, and clinical indication. **Hypomagnesemia:** * **IV:** 25-50 mg/kg/dose infused over 3-5 minutes, every 4-6 hours as needed. Maximum dose 2 grams. * **Maintenance:** 200-300 mg/kg/day (max 10 grams/day) divided into 3-4 doses and infused over 24 hours. **Eclampsia:** * **Loading Dose:** 40 mg/kg (max 2 grams) IV infused over 5-10 minutes. * **Maintenance Dose:** 10-15 mg/kg/hour (max 6 grams/day) IV infusion. **Torsades de Pointes:** * 25-50 mg/kg IV bolus (max 2 grams), followed by infusion of 10-20 mg/kg/hour (max 1 gram/hour). ## Dose Adjustments * **Renal Impairment:** Magnesium is renally excreted. Use with caution and monitor magnesium levels closely in patients with renal impairment. Dose reduction and/or less frequent administration may be necessary. ## Contraindications * Hypermagnesemia. * Heart block. * Myocardial infarction. * Digitalis toxicity. * Severe renal dysfunction (use with extreme caution). ## Adverse Effects * **Common:** Flushing, sweating, nausea, vomiting, hypotension, drowsiness, decreased deep tendon reflexes. * **Serious:** Respiratory depression, cardiac arrest, hypermagnesemia (leading to hypotension, bradycardia, ECG changes, respiratory paralysis, cardiac arrest). ## Key Drug Interactions * **Neuromuscular Blockers (e.g., rocuronium, succinylcholine):** Magnesium can potentiate neuromuscular blockade, increasing the risk of prolonged paralysis. * **Calcium Channel Blockers:** Increased risk of hypotension and bradycardia. * **Digoxin:** High doses of IV magnesium can potentially lead to digoxin toxicity in patients with impaired renal function. * **Nifedipine:** Concurrent use in preeclampsia may increase the risk of hypotension. ## Monitoring * **Magnesium levels:** Monitor serum magnesium levels regularly, especially during continuous infusions or with impaired renal function. Therapeutic range for hypomagnesemia is typically 1.7-2.2 mg/dL, but higher levels may be targeted for eclampsia. * **Renal function:** Assess creatinine and BUN. * **Vital signs:** Blood pressure, heart rate, respiratory rate. * **Deep tendon reflexes:** Monitor for loss of reflexes, an early sign of hypermagnesemia. * **Urine output:** Important for assessing renal function. * **ECG:** Especially in patients receiving high doses or with cardiac concerns. ## Clinical Pearls * Rapid IV infusion can cause hypotension, flushing, and cardiac arrhythmias. Infuse slowly as recommended. * Intramuscular injections can be painful; consider administering with lidocaine if available and appropriate. * Always have IV calcium available as an antidote for severe magnesium toxicity. * In patients with preeclampsia, monitor respiratory rate closely as hypermagnesemia can cause respiratory depression. *** *Disclaimer: This information is intended for healthcare professionals. Always consult the current prescribing information and relevant clinical guidelines for complete and up-to-date details before making any treatment decisions.*