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# Magnesium Sulfate ## Overview Magnesium sulfate is an essential mineral and electrolyte used to treat and prevent magnesium deficiency, manage pre-eclampsia and eclampsia, and treat torsades de pointes. It acts as a central nervous system depressant, a vasodilator, and a smooth muscle relaxant. ## Primary Indications * **Hypomagnesemia:** Treatment of magnesium deficiency. * **Preeclampsia and Eclampsia:** Prevention and treatment of seizures associated with severe preeclampsia and eclampsia. * **Torsades de Pointes:** Treatment of polymorphic ventricular tachycardia (torsades de pointes). * **Bronchodilator:** Adjunctive therapy in severe asthma exacerbations unresponsive to standard treatment. ## Adult Dosing * **Hypomagnesemia:** * **Severe Deficiency:** 4-6 grams IV initially, followed by 1-2 grams per hour infused IV until serum magnesium levels normalize. Alternatively, 1 gram IM every 6 hours for 4 doses. * **Less Severe Deficiency:** 2-4 grams IV or IM divided into multiple doses over 24 hours. * **Preeclampsia/Eclampsia Prophylaxis:** 4-5 grams IV infused over 15-20 minutes, followed by a maintenance infusion of 1-2 grams per hour. * **Eclampsia Treatment:** 4-5 grams IV infused over 5-20 minutes, followed by a continuous infusion of 1-2 grams per hour or IM doses of 5 grams into each buttock every 4 hours. * **Torsades de Pointes:** 1-2 grams diluted in 10-20 mL D5W IV push over 5-20 minutes. May repeat every 5-15 minutes. Follow with a continuous infusion of 0.5-1 gram per hour. * **Asthma (Adjunctive):** 1-2 grams IV infusion over 15-30 minutes. *Note: Specific dosing for preeclampsia/eclampsia may vary based on institutional protocol.* ## Pediatric Dosing * **Hypomagnesemia:** Dosing is highly variable and depends on severity and patient weight. Commonly cited doses range from 25-50 mg/kg per dose IV or IM, not to exceed 2 grams per dose. A continuous infusion of 10-30 mg/kg/hour may be used. Consult pediatric guidelines for precise dosing. * **Eclampsia:** Dosing is less well-established in pediatrics. Consult pediatric guidelines or specialist. A common regimen is a loading dose of 40 mg/kg IV over 30 minutes, followed by a maintenance infusion of 20 mg/kg/hour. * **Torsades de Pointes:** 25-50 mg/kg IV over 10-20 minutes, not to exceed 2 grams. May repeat every 10-15 minutes. Follow with a continuous infusion of 10-30 mg/kg/hour. ## Dose Adjustments * **Renal Impairment:** Magnesium is renally excreted. In patients with renal impairment, reduce the dose and monitor serum magnesium levels closely. Avoid in severe renal failure unless absolutely necessary and with extreme caution. ## Contraindications * Heart block * Hypermagnesemia * Hypocalcemia (relative contraindication, as magnesium can worsen hypocalcemia) * Myocardial infarction (relative contraindication in acute setting due to potential for hypotension) * Shock ## Adverse Effects * **Common:** Flushing, sweating, hypotension, nausea, vomiting, decreased deep tendon reflexes, somnolence, respiratory depression. * **Serious:** Cardiac arrhythmias, cardiac arrest, hypermagnesemia (muscle weakness, lethargy, respiratory paralysis, coma, cardiac arrest), hyperthermia, hypocalcemia. ## Key Drug Interactions * **Neuromuscular Blockers:** Magnesium can potentiate the effects of neuromuscular blocking agents, leading to prolonged muscle weakness or respiratory depression. * **Calcium Channel Blockers:** Additive hypotensive effects. * **Nifedipine:** Increased risk of hypotension and hyporeflexia. * **Tetracyclines and Bisphosphonates:** Magnesium can decrease the absorption of these drugs; separate administration by at least 2-3 hours. ## Monitoring * **Serum Magnesium Levels:** Monitor frequently, especially during IV infusions and in patients with renal impairment. Therapeutic range for hypomagnesemia treatment is typically 4-7 mg/dL. Target levels for eclampsia are often higher (4.8-8.4 mg/dL). * **Renal Function:** Assess baseline and monitor throughout therapy. * **Vital Signs:** Monitor blood pressure, heart rate, and respiratory rate closely. * **Deep Tendon Reflexes:** Assess for loss of reflexes, an early sign of hypermagnesemia. * **Urine Output:** Monitor for adequate output to ensure renal excretion. * **ECG:** Consider in patients receiving high doses or with risk factors for arrhythmias. ## Clinical Pearls * Always dilute magnesium sulfate for IV infusion. Rapid IV injection can cause hypotension and cardiac arrest. * Monitor for signs and symptoms of hypermagnesemia (e.g., absent deep tendon reflexes, decreased respiratory rate, hypotension). * Calcium gluconate or calcium chloride is the antidote for magnesium toxicity. Have it readily available when administering magnesium sulfate IV. * In preeclampsia/eclampsia, continuous monitoring of magnesium levels, reflexes, and respiratory status is crucial. *** *Disclaimer: This information is intended for healthcare professionals. It is essential to consult the most current prescribing information and relevant clinical guidelines before administering any medication. Dosing and safety considerations may vary based on patient-specific factors and institutional protocols.*