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# Magnesium Sulfate ## Overview Magnesium sulfate is an electrolyte supplement and anticonvulsant. It is available in parenteral (IV/IM) and oral formulations. ## Primary Indications * Treatment of hypomagnesemia. * Prevention and treatment of seizures in preeclampsia and eclampsia. * Management of status epilepticus refractory to first-line agents. * Treatment of torsades de pointes. * Adjunctive treatment for severe asthma exacerbations. ## Adult Dosing * **Hypomagnesemia:** * **Severe (serum magnesium < 1.3 mEq/L):** 4-6 grams (32-48 mEq) IV infusion over 10-60 minutes, followed by a continuous infusion of 1-2 grams (8-16 mEq) per hour. Daily maintenance is typically 2-4 grams (16-32 mEq). * **Less Severe (serum magnesium 1.3-1.7 mEq/L):** 2-4 grams (16-32 mEq) IV infusion over 5-60 minutes. * **IM:** 1 gram (8 mEq) every 4 hours as needed, up to 4 doses. * **Preeclampsia/Eclampsia Prophylaxis:** 4-5 grams (32-40 mEq) IV infusion over 15-30 minutes, followed by an infusion of 1-2 grams (8-16 mEq) per hour. * **Eclampsia Treatment (Seizure Management):** Loading dose of 4-5 grams (32-40 mEq) IV infusion over 5-10 minutes, followed by 1-2 grams (8-16 mEq) per hour IV infusion, or intermittent IV bolus of 2 grams (16 mEq) every 15 minutes for up to 1 hour. Alternatively, 5 grams (40 mEq) IM in each buttock for a total of 10 grams (80 mEq) may be given. *Local protocols may vary.* * **Torsades de Pointes:** 1-2 grams (8-16 mEq) IV in 10-20 mL D5W over 5-10 minutes. Can be followed by infusion of 0.5-1 gram (4-8 mEq) per hour. * **Asthma Exacerbation:** 1-2 grams (8-16 mEq) IV infusion in 50-100 mL normal saline over 15-30 minutes. ## Pediatric Dosing * **Hypomagnesemia:** Dosing is complex and depends on severity. * **Severe (serum magnesium < 1.3 mEq/L):** 25-50 mg/kg (0.1-0.2 mEq/kg) IV infusion over 10-30 minutes. Maximum dose: 2 grams (16 mEq). Followed by infusion of 20-30 mg/kg/hr (0.16-0.24 mEq/kg/hr). * **IM:** 25-50 mg/kg/dose every 4-6 hours. Maximum dose: 1 gram (8 mEq). * **Eclampsia Treatment (Seizure Management):** 25-50 mg/kg (0.1-0.2 mEq/kg) IV infusion over 10-30 minutes. Maximum dose: 2 grams (16 mEq). Followed by infusion of 20-30 mg/kg/hr (0.16-0.24 mEq/kg/hr). *Local protocols may vary.* * **Status Epilepticus:** 25-50 mg/kg/dose IV infusion, maximum 2 grams. * **Asthma Exacerbation:** 25-40 mg/kg IV infusion over 15-30 minutes. Maximum dose: 2 grams. ## Dose Adjustments * **Renal Impairment:** Use with caution. Reduce dose and monitor magnesium levels closely. In severe renal impairment, avoid parenteral administration if possible. ## Contraindications * Hypermagnesemia. * Heart block. * Myocardial infarction. * Pulmonary edema. * Shock. ## Adverse Effects * **Common:** Flushing, hypotension, somnolence, nausea, vomiting, decreased reflexes, diaphoresis. * **Serious:** Respiratory depression, cardiac arrhythmias, cardiac arrest, hypermagnesemia (muscle weakness, decreased deep tendon reflexes, difficulty breathing, hypotension, bradycardia, cardiac arrest), loss of deep tendon reflexes. ## Key Drug Interactions * **Neuromuscular Blockers:** Magnesium sulfate can potentiate neuromuscular blockade. * **Calcium Channel Blockers:** Increased risk of hypotension and bradycardia. * **Digitalis Glycosides:** Risk of digitalis toxicity, especially in the presence of hypokalemia and hypomagnesemia. * **Certain Antibiotics (e.g., tetracyclines, quinolones):** May decrease absorption if administered orally concurrently; separate administration by at least 2-3 hours. ## Monitoring * **Serum Magnesium Levels:** Crucial, especially with parenteral administration and in renal impairment. Therapeutic target for eclampsia is typically 4.0-7.0 mEq/L. * **Renal function (BUN, Creatinine).** * **Deep tendon reflexes.** * **Respiratory rate and depth.** * **Blood pressure and heart rate.** * **Urine output.** * **Electrocardiogram (ECG)** if cardiac concerns. ## Clinical Pearls * Parenteral magnesium sulfate is hypertonic; infuse slowly and dilute appropriately to avoid phlebitis or local irritation. * Monitor closely for signs and symptoms of hypermagnesemia, especially with impaired renal function or overdose. * Calcium gluconate or calcium chloride is the antidote for severe magnesium toxicity. * Oral magnesium can cause diarrhea. *** **Disclaimer:** This information is intended for clinical decision support and does not replace professional judgment. Always consult the most current prescribing information, institutional protocols, and patient-specific factors before making treatment decisions.