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# Magnesium Sulphate ## Overview Magnesium sulfate is an essential mineral involved in numerous biochemical reactions in the body, including neuromuscular transmission, cardiac excitability, and smooth muscle relaxation. ## Primary Indications * Treatment of hypomagnesemia. * Prevention and treatment of seizures in severe preeclampsia and eclampsia. * Management of torsades de pointes. * Treatment of status asthmaticus (adjunctive therapy). * Treatment of severe refractory hypokalemia. ## Adult Dosing * **Hypomagnesemia:** * **Severe deficiency:** 4-6 grams IV administered as a continuous infusion over 24 hours, or 1-2 grams IV every 4-8 hours. * **Moderate deficiency/maintenance:** 2-4 grams IV in 1 liter of D5W or NS over 4-12 hours, followed by 1-2 grams IV every 8-12 hours as needed. * **Oral replacement:** Dosing varies based on formulation and product labeling; typically 25-50 mEq per day divided into doses. * **Preeclampsia/Eclampsia:** * **Loading dose:** 4-6 grams IV over 5-20 minutes. * **Maintenance infusion:** 1-2 grams per hour IV. Adjustments may be made based on clinical response and serum magnesium levels. Maximum doses typically not strictly defined but guided by toxicity. * **Torsades de Pointes:** * **Initial bolus:** 1-2 grams IV in 10-50 mL of D5W over 5-10 minutes. * **Followed by infusion:** 0.5-1 gram per hour IV (may be higher in refractory cases). * **Status Asthmaticus:** 2 grams IV in 50-100 mL NS over 15-30 minutes. * **Refractory Hypokalemia:** Dosing varies based on potassium levels and clinical scenario; often administered in conjunction with potassium replacement. ## Pediatric Dosing * **Hypomagnesemia:** Dosing varies significantly by age and severity. A common regimen for severe deficiency is 25-50 mg/kg/dose IV every 4-6 hours, not to exceed adult doses. Oral dosing varies. * **Preeclampsia/Eclampsia:** Dosing similar to adults, with loading doses of 20-40 mg/kg (maximum 2 grams) and maintenance infusions of 10-20 mg/kg/hour (maximum 1 gram/hour). * **Status Asthmaticus:** 25-50 mg/kg/dose IV over 15-30 minutes, not to exceed 2 grams. * **Torsades de Pointes:** 25-50 mg/kg IV (maximum 2 grams). ## Dose Adjustments * **Renal Impairment:** Magnesium is renally excreted. Use with caution in patients with renal impairment. Doses should be reduced and serum magnesium levels closely monitored. In severe renal impairment, maintenance doses may need to be significantly reduced or avoided. ## Contraindications * Hypermagnesemia. * Heart block. * Myocardial infarction (use with caution). * Severe renal impairment (relative contraindication). ## Adverse Effects * **Common:** Flushing, hypotension, nausea, vomiting, diarrhea, somnolence, decreased deep tendon reflexes. * **Serious:** Respiratory depression, cardiac arrhythmias, cardiac arrest, complete heart block, neuromuscular blockade, hypermagnesemia (especially in renal impairment). ## Key Drug Interactions * **Neuromuscular Blockers (e.g., rocuronium, succinylcholine):** Magnesium can potentiate neuromuscular blockade, increasing the risk of prolonged paralysis and respiratory depression. * **Calcium Channel Blockers:** Additive hypotensive effects and risk of bradycardia or heart block. * **Antibiotics (tetracyclines, fluoroquinolones):** Magnesium can chelate with these antibiotics, reducing their absorption. Separate administration by at least 2-4 hours. * **Digoxin:** High doses of IV magnesium sulfate can potentially increase digoxin toxicity. ## Monitoring * **Serum Magnesium Levels:** Crucial for guiding dosing and preventing toxicity. Target levels vary by indication (e.g., 4-7 mEq/L for eclampsia). * **Renal Function:** Monitor BUN and creatinine. * **Vital Signs:** Blood pressure, heart rate, respiratory rate. * **Deep Tendon Reflexes:** Assess for loss of reflexes, an early sign of toxicity. * **Urine Output:** Maintain adequate urine output to facilitate magnesium excretion. * **ECG:** Monitor for signs of cardiac depression or arrhythmias. ## Clinical Pearls * Magnesium sulfate is a high-alert medication; always double-check doses. * Administer IV magnesium slowly to minimize side effects like flushing and hypotension. * Have calcium gluconate readily available as an antidote for severe magnesium toxicity. * Oral magnesium is often used for chronic hypomagnesemia or as a dietary supplement. * When treating hypomagnesemia, remember that concurrent hypokalemia and hypocalcemia may also be present and require correction. * Dosing for specific indications may vary based on institutional protocols and patient-specific factors. *** *This information is intended for clinical use and does not substitute for professional medical advice. Always consult the most current prescribing information and your institution's guidelines before administering any medication.*