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# Magnesium Sulphate ## Overview Magnesium is an essential mineral involved in numerous biochemical processes. Magnesium sulphate is the sulphate salt of magnesium, commonly used for its electrolyte replacement and pharmacological effects. ## Primary Indications * **Hypomagnesemia:** Treatment of low serum magnesium levels. * **Eclampsia/Preeclampsia:** Prevention and treatment of seizures associated with severe preeclampsia and eclampsia. * **Torsades de Pointes:** Treatment of polymorphic ventricular tachycardia associated with a prolonged QT interval. * **Bronchodilation:** As an adjunct therapy in severe asthma exacerbations unresponsive to standard treatment. * **Constipation:** As an osmotic laxative (less commonly used in this form). ## Adult Dosing * **Hypomagnesemia (Symptomatic or Severe):** * **IV:** 4-6 grams of anhydrous magnesium sulphate (equivalent to 32-48 mEq or 16-24 mmol elemental magnesium) infused over 5-60 minutes, followed by a maintenance infusion of 1-2 grams per hour. Dosage adjusted based on serum magnesium levels and renal function. * **IM:** 1 gram of anhydrous magnesium sulphate (equivalent to 8 mEq or 4 mmol elemental magnesium) every 6 hours for 4 doses, for a total of 4 grams. * **Eclampsia/Preeclampsia:** * **Loading Dose (IV):** 4-6 grams of anhydrous magnesium sulphate infused over 5-20 minutes. * **Maintenance Dose (IV):** 1-2 grams per hour via continuous infusion. * **Torsades de Pointes:** * **IV:** 1-2 grams of anhydrous magnesium sulphate in 100 mL of D5W infused over 5-10 minutes. May repeat bolus, followed by continuous infusion of 0.5-1 gram per hour. * **Severe Asthma (Adjunct):** * **IV:** 2 grams of anhydrous magnesium sulphate in 100 mL of normal saline infused over 15-20 minutes. ## Pediatric Dosing Dosing in pediatrics is highly variable and often guided by institutional protocols. General guidelines include: * **Hypomagnesemia:** * **IV:** 25-50 mg/kg (elemental magnesium) per dose, infused over 5-10 minutes. Maximum dose 2 grams. May be followed by continuous infusion of 5-15 mg/kg/hour. * **IM:** 25-50 mg/kg (elemental magnesium) per dose every 4-6 hours. * **Eclampsia/Preeclampsia:** Dosing typically follows adult guidelines adapted for weight. * **Torsades de Pointes:** * **IV:** 25-50 mg/kg (elemental magnesium) per dose, infused over 5-10 minutes. Maximum dose 2 grams. ## Dose Adjustments * **Renal Impairment:** Magnesium is renally excreted. Dose reduction is crucial in patients with impaired renal function to prevent hypermagnesemia. Monitor serum magnesium levels closely. In severe renal impairment, doses may need to be significantly reduced or withheld. ## Contraindications * Hypermagnesemia. * Heart block. * Myocardial infarction (caution). * Severe renal impairment (relative contraindication for higher doses). * Concurrent use of neuromuscular blocking agents (caution due to potential for additive neuromuscular blockade). ## Adverse Effects Common: Flushing, hypotension, nausea, vomiting, somnolence, decreased deep tendon reflexes, warmth. Serious: Respiratory depression, cardiac arrest, hypermagnesemia (leading to neuromuscular paralysis, hyporeflexia, hypotension, bradycardia, ECG changes, respiratory arrest, cardiac arrest). ## Key Drug Interactions * **Neuromuscular Blocking Agents (e.g., succinylcholine, vecuronium):** Magnesium can potentiate neuromuscular blockade, increasing the risk of prolonged paralysis and respiratory depression. * **Calcium Channel Blockers:** Additive hypotensive effects and potential for enhanced cardiodepression. * **Antibiotics (Tetracyclines, Quinolones):** Magnesium can decrease the absorption of oral tetracyclines and fluoroquinolones; administer at least 2 hours before or 4-6 hours after these antibiotics. * **Bisphosphonates:** Magnesium can decrease absorption; separate administration. ## Monitoring * **Serum Magnesium Levels:** Essential for guiding dosing, especially in hypomagnesemia and renal impairment. Target levels vary by indication. * **Renal Function:** Assess baseline and monitor during therapy, especially in renally impaired patients. * **Vital Signs:** Blood pressure, heart rate, respiratory rate. * **Neurological Status:** Level of consciousness, deep tendon reflexes. * **Urine Output:** Adequate urine output is necessary for magnesium excretion. * **ECG:** In patients receiving high doses or with cardiac concerns. ## Clinical Pearls * Always use anhydrous magnesium sulphate for calculations, as the hydrated form contains less elemental magnesium per gram. * IV infusions of magnesium sulphate should be administered slowly to prevent hypotension and flushing. Rapid infusion can cause cardiac arrest. * Discontinuation of magnesium therapy should be gradual in patients receiving prolonged high-dose infusions to avoid rebound hypomagnesemia. * In the setting of eclampsia, continuous cardiac and respiratory monitoring is essential. Loss of deep tendon reflexes can be an early sign of magnesium toxicity. *** *This information is intended for healthcare professionals. Always consult the most current prescribing information and relevant guidelines for complete details and to ensure patient safety.*