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# Magnesium Sulfate ## Overview Magnesium sulfate is an essential mineral that plays a crucial role in numerous biochemical reactions in the body, including neuromuscular transmission and muscle contraction. It is available in both intravenous (IV) and intramuscular (IM) formulations, as well as oral forms. ## Primary Indications * **Hypomagnesemia:** Treatment of magnesium deficiency. * **Eclampsia and Preeclampsia:** Prevention and treatment of seizures in pregnant women with preeclampsia and eclampsia. * **Torsades de Pointes:** Management of polymorphic ventricular tachycardia with a prolonged QT interval. * **Bronchodilator:** Adjunctive therapy in severe, acute bronchospasm, particularly in asthma exacerbations. ## Adult Dosing * **Hypomagnesemia:** * **Severe deficiency (serum Mg < 1.5 mEq/L):** 4-6 grams IV over 4-24 hours, followed by maintenance doses of 2-4 grams IV or IM every 12-24 hours as needed. * **Less severe deficiency (serum Mg 1.5-2.5 mEq/L):** 2-4 grams IV or IM given as a single dose or divided over several hours. * **Eclampsia/Preeclampsia (Loading Dose):** 4-6 grams IV infused over 5-10 minutes. * **Eclampsia/Preeclampsia (Maintenance Dose):** 1-2 grams IV per hour via continuous infusion, or 5 grams IM into each buttock every 4 hours. Dosing can be adjusted based on clinical response and serum magnesium levels. * **Torsades de Pointes:** 1-2 grams IV diluted in 10 mL of D5W and infused rapidly over 5-10 minutes. May repeat doses every 5-15 minutes. Continuous infusion of 1-2 grams per hour may be needed for ongoing management. * **Bronchodilator (Adjunctive):** 1-2 grams IV infused over 15-30 minutes. ## Pediatric Dosing Dosing for pediatric patients is highly variable and depends on the indication, age, and weight. Specific protocols are often utilized. * **Hypomagnesemia:** Dosing typically ranges from 25-50 mg/kg IV or IM per dose, not to exceed 2 grams per dose, given over 4-6 hours. Maintenance doses may be needed. * **Eclampsia/Preeclampsia:** Generally follows adult dosing guidelines adjusted for weight, but local protocols should be consulted. * **Bronchodilator:** 25-50 mg/kg IV infused over 15-30 minutes, typically with a maximum dose of 2 grams. ## Dose Adjustments * **Renal Impairment:** Magnesium is renally excreted. In patients with impaired renal function, magnesium sulfate should be used with extreme caution and doses reduced. Monitor serum magnesium levels closely. Patients with anuria may not be able to excrete magnesium and should not receive magnesium sulfate. ## Contraindications * **Hypermagnesemia:** Contraindicated in patients with hypermagnesemia. * **Heart Block:** Contraindicated in patients with heart block (unless a temporary pacemaker is in place). * **Myocardial Infarction:** Contraindicated in patients with myocardial infarction who are at risk for heart block. * **Hypersensitivity:** Known hypersensitivity to magnesium sulfate. ## Adverse Effects Common adverse effects include flushing, hypotension, nausea, vomiting, drowsiness, and lethargy. More serious adverse effects, particularly with excessive doses or rapid infusion, include: * **Cardiovascular:** Hypotension, bradycardia, cardiac arrest, ECG changes. * **Neuromuscular:** Loss of deep tendon reflexes, muscle weakness, respiratory depression, paralysis. * **Other:** Hyperthermia, diaphoresis, hypocalcemia, hyperkalemia. ## Key Drug Interactions * **Neuromuscular Blocking Agents:** Magnesium sulfate can potentiate the neuromuscular blockade of neuromuscular blocking agents (e.g., vecuronium, rocuronium). * **Calcium Channel Blockers:** Concurrent use may increase the risk of hypotension and neuromuscular blockade. * **Nifedipine:** Case reports suggest potential for profound hypotension and hyporeflexia when used together. ## Monitoring * **Serum Magnesium Levels:** Essential, especially in patients with renal impairment or those receiving continuous infusions. Target levels vary by indication. For eclampsia, levels of 4-7 mEq/L are generally targeted. * **Renal Function:** Monitor creatinine and BUN. * **Deep Tendon Reflexes:** Monitor for loss of reflexes, which can indicate magnesium toxicity. * **Respiratory Rate and Depth:** Monitor for signs of respiratory depression. * **Blood Pressure and Heart Rate:** Monitor for hypotension and bradycardia. * **Urine Output:** Should be adequate (> 100 mL in 4 hours) before administering subsequent doses in patients with preeclampsia/eclampsia. ## Clinical Pearls * Magnesium sulfate is a CNS depressant and can cause vasodilation. * Always ensure adequate renal function before administering. * IV administration should be slow and controlled to avoid adverse effects. * IM injections can be painful; consider Z-track technique and administering in divided doses if necessary. * Calcium gluconate or calcium chloride is the antidote for magnesium toxicity. *** **Disclaimer:** This information is intended for clinical use and does not substitute for professional medical judgment. Always consult the most current prescribing information and institutional protocols before administering any medication.