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# Magnesium Sulfate ## Overview Magnesium sulfate is an essential mineral that plays a role in numerous physiological processes, including neuromuscular transmission, muscle contraction, and enzyme activity. It is available in intravenous (IV) and intramuscular (IM) formulations. ## Primary Indications * Treatment of hypomagnesemia. * Management of pre-eclampsia and eclampsia. * Management of torsades de pointes. * Adjunctive treatment in severe exacerbations of asthma (less common, evidence is mixed). ## Adult Dosing * **Hypomagnesemia:** * **Severe:** 4-6 grams IV initially, followed by 1-2 grams/hour IV infusion as needed, based on serum magnesium levels. * **Less Severe:** 1-2 grams IV or IM every 4-6 hours for 3-4 doses. * **Maintenance:** 1 gram IV or IM every 6-12 hours. * **Pre-eclampsia/Eclampsia:** * **Loading Dose:** 4-6 grams IV infused over 15-20 minutes. * **Maintenance Infusion:** 1-2 grams/hour IV. Alternatively, IM doses of 5 grams every 4 hours into alternate buttocks may be used. Local protocols will dictate specific regimens. * **Torsades de Pointes:** * **With Pulse:** 1-2 grams IV in 10 mL D5W or NS, infused rapidly (over 5-20 minutes). May repeat. Further infusion at 0.5-1 gram/hour may be required. * **Without Pulse (ACLS Protocol):** 1-2 grams IV push. ## Pediatric Dosing * **Hypomagnesemia:** Dosing is highly variable and dependent on serum magnesium levels and clinical status. Typical IV doses range from 25-50 mg/kg per dose, infused over 3-6 hours. Maximum single IV dose is generally 2 grams. IM doses may be given. **Consult pediatric-specific guidelines or a pediatric specialist for precise dosing.** * **Eclampsia:** Similar to adults, with loading doses typically based on 40 mg/kg (maximum 4 grams) over 15-20 minutes, followed by maintenance infusions. **Consult pediatric-specific guidelines or a pediatric specialist for precise dosing.** * **Torsades de Pointes:** 25-50 mg/kg IV, maximum dose of 2 grams, infused over 10-20 minutes. ## Dose Adjustments Dose adjustments are primarily based on renal function and serum magnesium levels. In patients with impaired renal function, the dose and infusion rate should be reduced. Close monitoring of urine output is essential. ## Contraindications * Hypermagnesemia. * Heart block greater than first degree and myocardial damage (unless a pacemaker is present). * Hypersensitivity to magnesium sulfate. ## Adverse Effects Common adverse effects include flushing, warmth, hypotension, nausea, vomiting, decreased deep tendon reflexes, and respiratory depression. Hypermagnesemia can lead to cardiac arrest. ## Key Drug Interactions * **Neuromuscular Blockers:** Magnesium sulfate can potentiate the neuromuscular blockade produced by certain drugs (e.g., rocuronium, vecuronium), leading to prolonged paralysis. * **Calcium Salts:** IV calcium may be used as an antidote for severe hypermagnesemia. * **Nifedipine:** Concurrent use in pre-eclampsia may increase the risk of hypotension and muscle weakness. ## Monitoring * Serum magnesium levels (especially during prolonged infusions or in renal impairment). * Deep tendon reflexes. * Respiratory rate and effort. * Blood pressure. * Urine output. * Cardiac rhythm (particularly in torsades de pointes management or with rapid infusion). ## Clinical Pearls * Magnesium sulfate administration can cause a sensation of warmth or flushing. * Monitor for signs of hypermagnesemia (hypotension, bradycardia, decreased reflexes, somnolence, respiratory depression). * IV calcium gluconate or chloride is the antidote for hypermagnesemia. * Ensure adequate hydration and renal function before initiating therapy, especially for high-dose infusions. * When used for pre-eclampsia, continuous infusion is preferred over intermittent IM dosing due to more stable serum levels. *** **Disclaimer:** This information is intended for clinical professionals and does not replace a thorough review of the full prescribing information, relevant literature, and institutional protocols. Always verify current dosing, indications, and safety information with the official drug labeling and other authoritative sources before administering any medication.