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# Magnesium Sulfate ## Overview Magnesium sulfate is an essential mineral that plays a crucial role in numerous physiological processes, including neuromuscular function, cardiac rhythm, and enzyme activity. It is available for intravenous and intramuscular administration. ## Primary Indications * **Hypomagnesemia:** Treatment of low magnesium levels. * **Eclampsia/Preeclampsia:** Prevention and treatment of seizures in women with preeclampsia and eclampsia. * **Torsades de Pointes:** Treatment of polymorphic ventricular tachycardia associated with a prolonged QT interval. * **Status Asthmaticus:** Adjunctive therapy for severe asthma exacerbations refractory to standard treatment. ## Adult Dosing * **Hypomagnesemia:** * **Acute/Severe:** 4 to 12 grams intravenously (IV) or intramuscularly (IM) in the first 24 hours, followed by maintenance doses of 4 to 6 grams every 24 hours. * **Mild/Moderate:** 1 gram IV or IM every 6 hours for 4 doses. * *Specific daily dosing may vary based on protocol and serum magnesium levels.* * **Eclampsia/Preeclampsia (Loading Dose):** 4 to 6 grams IV infused over 5 to 20 minutes. * **Eclampsia/Preeclampsia (Maintenance Dose):** 1 to 2 grams IV per hour infusion. * *IM dosing is an alternative (5g IM into each buttock initially, then 5g IM every 4 hours).* * **Torsades de Pointes:** 1 to 2 grams IV, diluted in 10 mL of D5W, given as a bolus over 5 to 10 minutes, followed by an infusion of 0.5 to 1 gram per hour. * **Status Asthmaticus:** 2 grams IV diluted in 50 mL of normal saline infused over 15 to 20 minutes. ## Pediatric Dosing Dosing in pediatrics is highly variable and often guided by institutional protocols and specific indication. * **Hypomagnesemia:** Generally dosed based on elemental magnesium. A common range is 25 to 50 mg/kg per dose (elemental magnesium) IV or IM every 4 to 6 hours. Maximum single dose is typically 2 grams. * **Eclampsia/Preeclampsia:** Dosing often mirrors adult protocols, but adjustments are crucial based on weight and renal function. * **Torsades de Pointes:** 25 to 50 mg/kg (elemental magnesium) IV bolus over 10 to 20 minutes, followed by infusion. * **Status Asthmaticus:** 25 to 40 mg/kg (elemental magnesium) IV infusion over 15 to 30 minutes. ## Dose Adjustments * **Renal Impairment:** Magnesium is renally excreted. In patients with impaired renal function, doses should be reduced, and serum magnesium levels monitored closely to prevent accumulation and hypermagnesemia. ## Contraindications * Hypermagnesemia. * Heart block. * Myocardial infarction. * Atrioventricular (AV) block. * Severe renal impairment. ## Adverse Effects * **Common:** Flushing, sweating, hypotension, nausea, vomiting, decreased reflexes, drowsiness. * **Serious:** Respiratory depression, cardiac arrest, absent deep tendon reflexes, paralysis, coma, hypermagnesemia. ## Key Drug Interactions * **Neuromuscular Blocking Agents:** Magnesium sulfate can potentiate the effects of neuromuscular blockers, leading to prolonged muscle weakness or paralysis. * **Calcium Channel Blockers:** Additive hypotensive effects and potential for bradycardia or heart block. * **Antibiotics:** May decrease the absorption of tetracyclines and quinolone antibiotics when administered concurrently. Separate administration by at least 2-3 hours. * **Bisphosphonates:** May decrease absorption of bisphosphonates. Separate administration by at least 2 hours. ## Monitoring * **Serum Magnesium Levels:** Essential for guiding dosing and assessing efficacy and toxicity. Monitor frequently, especially during loading doses and in patients with renal impairment. * **Renal Function:** Monitor BUN, creatinine, and urine output. * **Vital Signs:** Blood pressure, heart rate, respiratory rate. * **Deep Tendon Reflexes:** Assess for loss of reflexes, an early sign of hypermagnesemia. * **Cardiac Rhythm:** Especially in patients receiving high doses or with underlying cardiac conditions. * **Urine Output:** Adequate urine output is critical for magnesium excretion. ## Clinical Pearls * Magnesium sulfate is typically administered as a 50% solution (4.07 mEq/mL or 2.03 mmol/mL elemental magnesium). * When administering IV, it must be diluted and infused slowly to avoid hypotension and adverse effects. * IM injections can be painful; consider lidocaine mixed with the injection. * Always have IV calcium gluconate readily available as an antidote in case of severe hypermagnesemia. * Discontinue infusion if signs of hypermagnesemia occur (e.g., loss of reflexes, hypotension, respiratory depression). *** *This information is intended for healthcare professionals. Always consult the most current prescribing information and relevant clinical guidelines before making any treatment decisions.*