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# Magnesium Sulfate ## Overview Magnesium sulfate is an inorganic salt that acts as a central nervous system depressant and an anticonvulsant. It also has smooth muscle relaxant properties. ## Primary Indications * Treatment of hypomagnesemia. * Prevention and treatment of seizures in preeclampsia and eclampsia. * Management of torsades de pointes. * Bronchodilation in severe asthma exacerbations (off-label use). ## Adult Dosing * **Hypomagnesemia:** * Intramuscular (IM): 1-4 grams (8-32 mEq) every 6 hours as needed. * Intravenous (IV): 1-4 grams (8-32 mEq) in 250-1000 mL of IV fluid over 1-4 hours. Repeat doses may be given based on serum magnesium levels and clinical response. * **Preeclampsia/Eclampsia:** * Loading dose: 4-6 grams (32-48 mEq) IV over 5-20 minutes. * Maintenance dose: 1-2 grams (8-16 mEq) per hour via continuous IV infusion. May be adjusted based on seizure control and toxicity. * IM (alternative): 5 grams (40 mEq) in each buttock for the loading dose, followed by 5 grams (40 mEq) IM into alternate buttocks every 4 hours. * **Torsades de Pointes:** * IV: 1-2 grams (8-16 mEq) in 10-20 mL of D5W or NS over 5-10 minutes. May be followed by a continuous infusion of 0.5-1 gram (4-8 mEq) per hour. * **Severe Asthma Exacerbation (off-label):** * IV: 1-2 grams (8-16 mEq) in 50-100 mL of NS or D5W over 15-30 minutes. ## Pediatric Dosing Dosing in children is highly variable and should be guided by specific protocols and expert consultation. General guidelines: * **Hypomagnesemia:** * IV: 20-50 mg/kg/dose (0.1-0.4 mEq/kg/dose) every 4-6 hours as needed, not to exceed 1-2 grams (8-16 mEq) per dose for severe deficiency. * IM: 25-50 mg/kg/dose every 4-6 hours. * **Eclampsia:** * Loading dose: 40 mg/kg (0.32 mEq/kg) IV over 5-10 minutes. * Maintenance dose: 10-15 mg/kg/hour (0.08-0.12 mEq/kg/hour) IV infusion. ## Dose Adjustments * **Renal Impairment:** Use with caution. Magnesium is renally excreted. In patients with severe renal impairment, doses should be significantly reduced, and magnesium levels monitored closely to avoid accumulation and toxicity. ## Contraindications * Hypermagnesemia. * Heart block. * Myocardial infarction. * Digitalis toxicity. * Severe renal impairment (caution advised). ## Adverse Effects * **Common:** Flushing, warmth, hypotension, nausea, vomiting, diarrhea, drowsiness, lethargy, decreased deep tendon reflexes. * **Serious:** Respiratory depression, cardiac arrhythmias, cardiac arrest, complete heart block, hypermagnesemia toxicity (e.g., loss of deep tendon reflexes, decreased respiratory rate, altered mental status, hypotension, bradycardia, cardiac arrest). ## Key Drug Interactions * **Neuromuscular Blockers:** May potentiate neuromuscular blockade, leading to prolonged muscle weakness or paralysis. * **Calcium Channel Blockers:** May increase the risk of hypotension and bradycardia. * **Digitalis Glycosides:** Concomitant use with IV magnesium can lead to digitalis toxicity if hypermagnesemia occurs. * **Antibiotics:** Parenteral magnesium may decrease the efficacy of tetracyclines and quinolone antibiotics by forming insoluble complexes. Administer at least 2-3 hours apart. ## Monitoring * **Clinical:** Monitor for signs of seizure control (for preeclampsia/eclampsia), respiratory rate, blood pressure, heart rate, level of consciousness, and deep tendon reflexes. * **Laboratory:** Monitor serum magnesium levels, especially with IV infusions or in patients with renal impairment. Recommended therapeutic range for eclampsia prophylaxis is typically 4-7 mEq/L. Monitor renal function (BUN, creatinine) and electrolytes (calcium). ## Clinical Pearls * IV administration is generally preferred for rapid effect and easier titration. * When administering IV magnesium, ensure calcium gluconate is readily available as an antidote for hypermagnesemia. * Rapid IV infusion can cause hypotension and cardiac arrhythmias. Infuse slowly as recommended. * Diarrhea is a common side effect of oral magnesium supplements. * Magnesium sulfate can cause uterine relaxation, which may be beneficial in preterm labor but can also prolong labor. *** **Disclaimer:** This information is intended for healthcare professionals. It is essential to consult the most current prescribing information, product monographs, and institutional protocols for definitive guidance. Dosing and management may vary based on patient-specific factors and clinical context.