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# Magnesium Sulfate ## Overview Magnesium sulfate is an electrolyte and osmotic laxative. It is administered intravenously for the treatment of eclampsia, torsades de pointes, and severe asthma exacerbations, and orally as a laxative. ## Primary Indications * **Intravenous (IV):** Treatment of eclampsia, treatment of torsades de pointes, adjunctive treatment of severe asthma exacerbations. * **Oral:** Treatment of occasional constipation. ## Adult Dosing * **Eclampsia:** Loading dose: 4-6 grams IV infused over 5-20 minutes, followed by maintenance infusion of 1-2 grams/hour. Some protocols may use intramuscular (IM) administration. * **Torsades de Pointes:** 1-2 grams IV diluted in 10-20 mL of D5W or normal saline, infused over 5-10 minutes. May repeat. * **Asthma Exacerbation:** 2 grams IV diluted in 50-100 mL of normal saline, infused over 15-30 minutes. * **Constipation:** 15-30 mL of a 50% oral solution as a single dose. Onset of laxative effect is typically 30 minutes to 6 hours. ## Pediatric Dosing * **Eclampsia:** Pediatric dosing is not well-established. Consult specialist literature or local protocol. * **Torsades de Pointes:** 25-50 mg/kg IV infused over 10-20 minutes. Maximum dose 2 grams. * **Asthma Exacerbation:** 25-50 mg/kg IV infused over 15-30 minutes. Maximum dose 2 grams. * **Constipation:** Oral dosing varies by age and product concentration. For children 6-12 years: 5-10 mL of a 50% oral solution. For children under 6 years: consult product labeling or specialist. ## Dose Adjustments * **Renal Impairment:** Magnesium is renally excreted. Use with caution in patients with renal impairment. Monitor serum magnesium levels closely. Dose reduction may be necessary. Avoid in severe renal failure. ## Contraindications * Known hypersensitivity to magnesium sulfate. * Heart block. * Myocardial infarction. * Hypermagnesemia. * Intestinal obstruction or perforation (for oral administration). * Anuria or significant renal dysfunction (relative contraindication for IV use). ## Adverse Effects * **Common (especially with IV):** Flushing, hypotension, somnolence, diaphoresis, nausea, vomiting. * **Serious:** Hypermagnesemia (lethargy, weakness, hyporeflexia, respiratory depression, cardiac arrhythmias, cardiac arrest), pulmonary edema, severe hypotension. ## Key Drug Interactions * **Neuromuscular Blocking Agents:** Magnesium can potentiate neuromuscular blockade, leading to prolonged respiratory depression. * **Calcium Channel Blockers:** Additive hypotensive effects and increased risk of neuromuscular blockade. * **Digoxin:** Risk of digoxin toxicity if hypermagnesemia occurs. * **Tetracyclines and Quinolones:** Oral magnesium sulfate can decrease the absorption of these antibiotics. Separate administration by at least 2 hours. ## Monitoring * **For IV use:** * Vital signs (blood pressure, heart rate, respiratory rate). * Deep tendon reflexes. * Urine output. * Serum magnesium levels (especially in renal impairment or prolonged infusions). Target therapeutic levels are typically 4-7 mEq/L for eclampsia, and 2-4 mEq/L for torsades/asthma. * ECG if cardiac effects are suspected. * **For Oral use:** * Bowel movements. * Electrolytes if used chronically or in patients with renal impairment. ## Clinical Pearls * Magnesium sulfate is a "CNS depressant" and can cause hyporeflexia, respiratory depression, and hypotension at higher doses. * Ensure IV infusion is properly diluted and administered at the prescribed rate to avoid rapid increases in serum magnesium, which can lead to cardiac arrest. * Monitor for signs of hypermagnesemia, particularly in patients with impaired renal function. * Oral magnesium sulfate should not be used for chronic constipation as it can lead to dependence and electrolyte disturbances. *** *This information is intended for healthcare professionals. It is essential to consult the most current prescribing information and relevant clinical guidelines for complete details before making therapeutic decisions. Dosing may vary based on specific patient factors and institutional protocols.*