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# Magnesium Sulphate ## Overview Magnesium sulphate is an inorganic salt providing elemental magnesium. It is available in various formulations for parenteral and oral administration. ## Primary Indications * **Hypomagnesemia:** Treatment of magnesium deficiency. * **Eclampsia/Preeclampsia:** Prevention and treatment of seizures associated with severe preeclampsia and eclampsia. * **Torsades de Pointes:** Treatment of polymorphic ventricular tachycardia, particularly in the setting of a prolonged QT interval. * **Bronchodilator:** Adjunctive treatment in severe, refractory asthma. * **Laxative:** Oral formulation for short-term relief of occasional constipation. ## Adult Dosing * **Hypomagnesemia:** * **Severe:** 4-6 g IV infusion over 4-12 hours. May repeat daily as needed. * **Mild to Moderate:** 1-2 g IV infusion over 1-4 hours. May repeat every 4-6 hours as needed. * **IM:** 1 g IM every 4 hours for 4 doses. * **Oral:** 30 mL of a 50% solution (15 g) initially, followed by 15 mL (7.5 g) every 4 hours as needed. Max oral daily dose is 30 g. * **Eclampsia/Preeclampsia:** Loading dose of 4-6 g IV infused over 5-10 minutes, followed by a maintenance infusion of 1-2 g/hour. Alternatively, 5 g IM into each buttock (total 10g) followed by 5 g IM every 4 hours. Specific protocols may vary. * **Torsades de Pointes:** 1-2 g IV diluted in 10-20 mL D5W given as a rapid IV infusion over 5-10 minutes. Further doses of 0.5-1 g/hour may be administered as a continuous infusion. * **Bronchodilator (Severe Asthma):** 1-2 g IV infusion over 15-20 minutes. ## Pediatric Dosing * **Hypomagnesemia:** Dosing varies significantly based on age and severity. A common approach for IV administration is 25-50 mg/kg/dose (elemental magnesium) infused over 1-4 hours, not to exceed 1 g per dose. May repeat every 4-12 hours. Oral dosing is also highly variable. Consult specialized pediatric resources. * **Eclampsia/Preeclampsia:** Dosing is typically based on adult guidelines, but weight-based adjustments may be considered in certain situations. Consult obstetrical protocols. * **Torsades de Pointes:** 25-50 mg/kg IV (elemental magnesium) as a rapid infusion over 5-10 minutes. May repeat as needed. Maximum dose usually 2 g. ## Dose Adjustments * **Renal Impairment:** Magnesium is renally excreted. Reduce dose in patients with impaired renal function. Monitor serum magnesium levels closely. Dose reductions may be substantial, particularly in severe renal impairment. ## Contraindications * Myasthenia gravis. * Heart block. * Hypermagnesemia. * Hypersensitivity to magnesium sulphate. * Marked renal impairment (caution/dose adjustment needed). ## Adverse Effects * **Common:** Flushing, sweating, nausea, vomiting, diarrhea (oral), hypotension, drowsiness, decreased deep tendon reflexes. * **Serious:** Respiratory depression, cardiac arrhythmias, cardiac arrest, hypermagnesemia (especially with renal impairment), hyperthermia. ## Key Drug Interactions * **Neuromuscular Blockers:** Potentiates neuromuscular blockade. * **Calcium Salts:** May antagonize the effects of magnesium. * **Tetracyclines and Quinolones:** Magnesium can decrease the absorption of these antibiotics. Administer at least 2 hours before or 4-6 hours after. * **Bisphosphonates:** Magnesium can decrease the absorption of bisphosphonates. Administer at least 2 hours before. ## Monitoring * **Serum Magnesium Levels:** Crucial, especially with IV administration and in renal impairment. Target levels vary by indication. * **Renal Function:** Monitor creatinine and BUN. * **Deep Tendon Reflexes:** Assess for loss of reflexes, an early sign of hypermagnesemia. * **Respiratory Rate and Effort:** Monitor for signs of respiratory depression. * **Cardiac Rhythm:** Especially important in torsades de pointes and with high doses. * **Blood Pressure:** Monitor for hypotension. ## Clinical Pearls * Rapid IV infusion can cause hypotension and flushing. Administer IV infusions slowly. * Magnesium sulphate is a CNS depressant. * Always use an infusion pump for IV magnesium administration. * Magnesium administration can mask hypokalemia and hypocalcemia. **Disclaimer:** This information is intended for healthcare professionals. Always verify current prescribing information and consult appropriate resources for specific patient management. Dosing may vary based on institutional protocols and individual patient factors.