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# Magnesium Sulphate ## Overview Magnesium sulphate is an inorganic salt used to treat or prevent magnesium deficiency, and as a smooth muscle relaxant. It is available intravenously and intramuscularly. ## Primary Indications * **Hypomagnesemia:** Treatment of severe magnesium deficiency. * **Eclampsia/Preeclampsia:** Prevention and treatment of seizures associated with severe preeclampsia and eclampsia. * **Torsades de Pointes:** Treatment of polymorphic ventricular tachycardia (torsades de pointes) associated with a prolonged QT interval. * **Bronchodilator:** Adjunctive therapy in severe acute asthma refractory to standard treatment. ## Adult Dosing * **Hypomagnesemia:** * **Acute Replenishment (Severe Deficiency):** 4-6 grams IV administered over 5-10 minutes, followed by a continuous infusion of 1-2 grams per hour. Maximum infusion rate typically 1-2 grams/hour. Daily maintenance usually 1-2 grams IV or IM divided every 4-6 hours. * **Chronic Replenishment:** Dosing varies based on serum magnesium levels and renal function. * **Eclampsia/Preeclampsia:** 4-6 grams IV loading dose, followed by 1-2 grams per hour IV infusion. Alternative IM regimen: 4-5 grams IM in each buttock (8-10 grams total) for loading, followed by 5 grams IM every 4 hours. Dosing often dictated by institutional protocol. * **Torsades de Pointes:** 1-2 grams IV bolus over 5-10 minutes, followed by an infusion of 0.5-1 gram per hour. * **Asthma (Adjunctive):** 1-2 grams IV infusion over 15-20 minutes. ## Pediatric Dosing * **Hypomagnesemia:** * **Acute Replenishment:** 25-50 mg/kg/dose IV over 10-15 minutes. May be followed by a continuous infusion of 20-30 mg/kg/hour. Maximum dose varies but often around 1-2 grams. * **Maintenance:** 10-20 mg/kg/dose IV or IM every 4-6 hours. * **Eclampsia/Preeclampsia:** Dosing for pregnant women is the same as adult dosing. Safety and efficacy in pediatric eclampsia are not well established; dosing is often extrapolated from adult guidelines or specific pediatric protocols. * **Torsades de Pointes:** 25-50 mg/kg IV bolus over 10-30 minutes. * **Asthma (Adjunctive):** 25-50 mg/kg IV infusion over 15-30 minutes. ## Dose Adjustments * **Renal Impairment:** Magnesium is renally excreted. In patients with impaired renal function, reduce the dose and monitor serum magnesium levels closely. Avoid in severe renal failure if possible, or use with extreme caution and close monitoring. ## Contraindications * Hypermagnesemia * Heart block (second or third degree) * Myocardial damage * Hypersensitivity to magnesium sulphate ## Adverse Effects Common: Flushing, sweating, hypotension, nausea, vomiting, diarrhea, drowsiness, muscle weakness. Serious: Respiratory depression, cardiac arrhythmias, cardiac arrest, hypermagnesemia (especially in renal impairment). ## Key Drug Interactions * **Neuromuscular Blockers (e.g., rocuronium, succinylcholine):** Magnesium can potentiate neuromuscular blockade, leading to prolonged muscle weakness or respiratory depression. * **Calcium Salts:** May antagonize the cardiac effects of magnesium. * **Tetracyclines and Bisphosphonates:** Magnesium can reduce the absorption of oral tetracyclines and bisphosphonates. Separate administration by at least 2-3 hours. * **Calcium Channel Blockers:** Additive hypotensive effects and increased risk of cardiac depression. ## Monitoring * **Serum Magnesium Levels:** Crucial, especially during IV infusions and in patients with renal impairment. Therapeutic range varies by indication. * **Renal Function:** Monitor BUN and creatinine. * **Deep Tendon Reflexes:** Loss of reflexes can indicate hypermagnesemia. * **Respiratory Rate and Effort:** Monitor for signs of respiratory depression. * **Blood Pressure and Heart Rate:** Monitor for hypotension and arrhythmias. * **Urine Output:** Adequate renal function is necessary for magnesium excretion. ## Clinical Pearls * When administered IV, dilute magnesium sulphate in a compatible IV fluid (e.g., D5W, NS) and infuse slowly to avoid hypotension and flushing. * IM injections can be painful; consider using a larger muscle mass and a dilute solution if necessary. * Magnesium plays a role in numerous cellular functions including nerve impulse transmission and muscle contraction. * In eclampsia, magnesium sulphate is the drug of choice for seizure prophylaxis and treatment. *** **Disclaimer:** This information is intended for healthcare professionals. Always consult the most current prescribing information and institutional protocols before administering any medication.