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# Magnesium Sulfate ## Overview Magnesium sulfate is an essential mineral that plays a role in numerous biochemical reactions, including neuromuscular transmission and muscle contraction. It is available for intravenous (IV) and intramuscular (IM) administration, as well as oral and topical forms, though IV is most common for acute indications. ## Primary Indications * **Hypomagnesemia:** Treatment of documented magnesium deficiency. * **Preeclampsia/Eclampsia:** Prevention and treatment of seizures in preeclamptic and eclamptic patients. * **Torsades de Pointes:** Treatment of polymorphic ventricular tachycardia associated with a prolonged QT interval. * **Status Asthmaticus:** Adjunctive therapy in severe acute asthma exacerbations refractory to standard treatment. ## Adult Dosing * **Hypomagnesemia:** * **Severe deficiency (<1 mg/dL):** 4-6 grams IV initially, followed by 1-2 grams/hour infusion for up to 24 hours or until serum magnesium levels are therapeutic. * **Mild deficiency (1-1.5 mg/dL):** 2-4 grams IV or IM daily in divided doses for 2-4 days. * Alternatively, 1 gram IM every 6 hours for 4 doses. * **Preeclampsia/Eclampsia:** * **Loading dose:** 4-6 grams IV, infused over 5-10 minutes. * **Maintenance infusion:** 1-2 grams/hour IV. * **IM administration (alternative):** 5 grams IM in each buttock, followed by 5 grams IM every 4 hours as needed. * **Torsades de Pointes:** 1-2 grams IV diluted in 10 mL D5W, infused over 5-10 minutes. May repeat dose if needed. Further infusion may be given based on clinical response and magnesium levels. * **Status Asthmaticus:** 2 grams IV diluted in 100 mL NS or SWFI, infused over 15-20 minutes. ## Pediatric Dosing Dosing is highly variable and often weight-based and indication-specific. Consult pediatric guidelines. * **Hypomagnesemia:** * **Severe:** 25-50 mg/kg/dose IV infused over 10 minutes to 1 hour. Maximum single dose 2 grams. May repeat every 4-6 hours. * **Less severe:** 50 mg/kg/day divided into 3-4 doses IV or IM. Maximum 1 gram/day. * **Eclampsia:** Similar to adults, but specific protocols should be followed, often starting with 20-30 mg/kg IV. ## Dose Adjustments * **Renal Impairment:** Magnesium is renally excreted. Use with caution in patients with impaired renal function. Dosage reduction and/or increased monitoring is recommended. Avoid in severe renal failure if possible. ## Contraindications * Hypermagnesemia. * Heart block (especially AV block). * Myocardial infarction. * Hyperkalemia (with caution, can worsen). * Severe renal dysfunction. ## Adverse Effects * **Common:** Flushing, sweating, hypotension, somnolence, nausea, vomiting. * **Serious:** Respiratory depression, cardiac arrhythmias, cardiac arrest, loss of deep tendon reflexes, muscle weakness, hypocalcemia, hyperkalemia, seizures (paradoxical). ## Key Drug Interactions * **Neuromuscular Blockers (e.g., succinylcholine, rocuronium):** Magnesium can potentiate neuromuscular blockade, leading to prolonged paralysis. * **Calcium Salts:** May antagonize the cardiac effects of magnesium. * **Potassium Salts:** Concurrent use can lead to hyperkalemia. * **Tetracyclines and Quinolones:** Magnesium can decrease the absorption of oral forms of these antibiotics; separate administration by at least 2-3 hours. ## Monitoring * **Serum magnesium levels:** Regularly monitor, especially with prolonged infusions or in renal impairment. Therapeutic levels typically range from 2-3.5 mg/dL for hypomagnesemia treatment, though higher levels may be targeted for eclampsia. * **Renal function (BUN, creatinine).** * **Deep tendon reflexes:** Assess for loss of reflexes, indicating hypermagnesemia. * **Respiratory rate and depth:** Monitor for signs of respiratory depression. * **Blood pressure and heart rate.** * **Urine output:** Monitor for adequate renal function. * **ECG:** Particularly when treating torsades de pointes or if cardiac effects are suspected. ## Clinical Pearls * IV administration should be slow and controlled, as rapid infusion can cause hypotension and cardiac depression. * Always dilute magnesium sulfate for IV infusion to avoid vein irritation and phlebitis. * In patients with impaired renal function, monitor magnesium levels closely and be prepared to reduce dose or discontinue. * When treating eclampsia, magnesium sulfate is preferred over phenytoin or diazepam for seizure prophylaxis and treatment. *** **Disclaimer:** This information is intended for healthcare professionals. Always consult the official prescribing information and relevant guidelines for complete details and to verify current recommendations before making any clinical decisions.