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# Magnesium Sulphate ## Overview Magnesium sulfate is an electrolyte used for various indications, including the treatment of hypomagnesemia, eclampsia, and as a tocolytic agent. ## Primary Indications * Treatment of hypomagnesemia. * Prevention and treatment of seizures in preeclampsia and eclampsia. * Tocolysis (inhibition of premature labor). * Management of severe asthma exacerbations (adjunctive therapy). * Treatment of torsades de pointes. ## Adult Dosing * **Hypomagnesemia:** * **Acute/Severe:** 4-6 grams intravenously (IV) over 5-20 minutes, followed by 1-2 grams per hour as a continuous infusion, adjusted based on serum magnesium levels and clinical response. Maintenance doses are typically 2-4 grams every 4-12 hours. * **Chronic/Mild:** 1 gram intramuscularly (IM) or orally every 6 hours for 4 doses. Oral magnesium oxide 800-1200 mg daily can also be used for mild deficiency. * **Preeclampsia/Eclampsia:** Loading dose of 4-6 grams IV infused over 5-10 minutes. Maintenance infusion of 1-2 grams per hour. Dosing may vary based on local protocol and patient response. IM dosing (e.g., 5g IM in each buttock) may be used if IV access is limited. * **Tocolysis:** 4-6 grams IV loading dose over 20-30 minutes, followed by an infusion of 2-4 grams per hour. Duration is typically limited to 24-48 hours. * **Torsades de Pointes:** 1-2 grams IV in 10 mL of D5W over 5-10 minutes. May be followed by an infusion of 0.5-1 gram per hour. ## Pediatric Dosing Dosing is highly variable and depends on indication and patient weight. Consult specific pediatric guidelines or protocols. * **Hypomagnesemia:** Typically 25-50 mg/kg/dose IV or IM every 4-6 hours. Maximum dose usually 2 grams. * **Eclampsia:** Dosing is often based on adult protocols scaled by weight, but specific pediatric protocols should be followed. ## Dose Adjustments * **Renal Impairment:** Magnesium is renally excreted. In patients with impaired renal function, reduce the dose and monitor serum magnesium levels closely to prevent accumulation and toxicity. ## Contraindications * Hypermagnesemia. * Heart block. * Myocardial infarction (caution). * Cerebral infarction (caution). * Severe renal failure. * Myasthenia gravis. ## Adverse Effects Common: Flushing, hypotension, nausea, vomiting, drowsiness, decreased reflexes, and diaphoresis. Serious: Respiratory depression, cardiac arrhythmias, cardiac arrest, loss of deep tendon reflexes, and coma. ## Key Drug Interactions * **Neuromuscular Blockers (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 neuromuscular blockade. * **Nifedipine:** Increased risk of hypotension, especially when used for tocolysis. * **Tetracyclines and Fluoroquinolones:** Magnesium can decrease the absorption of oral forms of these antibiotics. Administer at least 2 hours before or 4-6 hours after magnesium. ## Monitoring * **Serum Magnesium Levels:** Monitor frequently, especially during IV infusion and in patients with renal impairment. Therapeutic range for eclampsia is typically 4-7 mEq/L. * **Renal Function:** Assess baseline and monitor during therapy. * **Deep Tendon Reflexes:** Assess before each dose; loss of reflexes indicates hypermagnesemia. * **Respiratory Rate and Effort:** Monitor for signs of respiratory depression. * **Blood Pressure and Heart Rate:** Monitor for hypotension and cardiac effects. * **Urine Output:** Ensure adequate renal function. ## Clinical Pearls * IV administration can cause transient hypotension, especially with rapid infusion. * Monitor for signs of magnesium toxicity closely, particularly in patients with renal impairment. * Calcium gluconate (1 gram IV) is the antidote for magnesium toxicity. * Magnesium sulfate is teratogenic in animal studies; use in pregnancy should be carefully considered based on risk-benefit. *** **Disclaimer:** This information is intended for healthcare professionals. Always consult the most current prescribing information and institutional protocols for complete details and to verify dosing and safety.