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# Magnesium Sulfate ## Overview Magnesium sulfate is an electrolyte that plays a crucial role in numerous biochemical functions, 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 status epilepticus refractory to other agents. * Treatment of torsades de pointes. * Management of bronchospasm in severe asthma exacerbations. ## Adult Dosing * **Hypomagnesemia:** * **Severe deficiency (serum Mg < 1.5 mEq/L):** 4-6 grams IV initially, followed by 2-4 grams IV every 4-12 hours as needed. Maintenance may be 4-12 grams IV over 24 hours. * **Less severe deficiency:** 1-2 grams IV or IM in divided doses over several hours. * **Preeclampsia/Eclampsia:** 4-6 grams IV loading dose over 5-10 minutes, followed by a maintenance infusion of 1-2 grams/hour IV. Alternatively, 5 grams IM in each buttock initially, followed by 5 grams IM every 4 hours. * **Status Epilepticus (refractory):** 2-4 grams IV over 10-20 minutes. * **Torsades de Pointes:** 1-2 grams IV in 5-10 minutes, followed by an infusion of 0.5-1 gram/hour. * **Bronchospasm (severe asthma):** 1-2 grams IV over 15-30 minutes. Dosing is highly dependent on serum magnesium levels and clinical response. Renal impairment requires dose adjustment. ## Pediatric Dosing Dosing in pediatric patients is less well-established and often based on weight and clinical scenario. Local protocols and expert consultation are recommended. * **Hypomagnesemia:** Typically 20-50 mg/kg/dose IV or IM every 6-12 hours. Maximum single dose generally 2 grams. * **Preeclampsia/Eclampsia (Maternal):** Dosing may follow adult guidelines. * **Status Epilepticus:** 25-100 mg/kg/dose IV, maximum 2 grams. ## Dose Adjustments * **Renal Impairment:** Use with caution. Reduce dose and monitor serum magnesium closely. In severe renal impairment, avoid if possible or use very low doses. ## Contraindications * Hypermagnesemia. * Heart block (greater than first degree) or myocardial damage (unless used with cardiac monitoring in an emergency). * Known hypersensitivity to magnesium sulfate. ## Adverse Effects * **Common:** Flushing, hypotension, nausea, vomiting, drowsiness, decreased reflexes, muscle weakness. * **Serious:** Respiratory depression, cardiac arrest, hypermagnesemia (characterized by lethargy, confusion, hyporeflexia, hypotension, bradycardia, respiratory depression, and cardiac arrest). ## Key Drug Interactions * **Neuromuscular blocking agents:** Potentiates neuromuscular blockade. * **Calcium channel blockers:** Increased risk of hypotension and neuromuscular blockade. * **Nifedipine:** Increased risk of hypotension when co-administered for preeclampsia. * **Other CNS depressants:** Additive CNS depression. ## Monitoring * **Magnesium levels:** Monitor serum magnesium levels, especially with prolonged infusions, impaired renal function, or in pediatric patients. Target levels vary by indication (e.g., 4-7 mEq/L for eclampsia). * **Renal function:** Monitor serum creatinine and BUN. * **Vital signs:** Blood pressure, heart rate, respiratory rate. * **Deep tendon reflexes:** Assess for loss of reflexes, an early sign of hypermagnesemia. * **Urine output:** Monitor for adequate renal function. * **ECG:** Consider for patients receiving high doses or with cardiac risk factors. ## Clinical Pearls * Magnesium sulfate administration can cause flushing and a sensation of heat, which is typically transient. * Administer IV infusions slowly to minimize hypotension and other adverse effects. * Always ensure adequate renal function before administering magnesium sulfate. * In hypomagnesemia, potassium and calcium levels should also be monitored and corrected as necessary, as they are often depleted concurrently. * For intramuscular administration, split the dose between two large muscle masses to reduce pain and risk of sterile abscess. *** *Disclaimer: This information is intended for healthcare professionals. Always consult the most current prescribing information and relevant guidelines before making any clinical decisions.*