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# Magnesium Sulphate ## Overview Magnesium sulphate is an electrolyte. It is an essential mineral involved in numerous enzymatic reactions and neuromuscular function. ## Primary Indications * Treatment of hypomagnesemia. * Management of eclampsia and pre-eclampsia. * Management of torsades de pointes. * Adjunctive treatment in severe asthma exacerbations. * Prevention and treatment of cardiac arrhythmias associated with hypokalemia or hypomagnesemia. ## Adult Dosing * **Hypomagnesemia:** * **Acute symptomatic hypomagnesemia:** 4 to 6 grams (32 to 48 mEq) IV over 5 to 10 minutes, followed by 1 to 2 grams (8 to 16 mEq) per hour as a continuous infusion, adjusted based on serum magnesium levels and clinical response. Maximum rate of infusion for initial dose typically 1g/min. * **Chronic or asymptomatic hypomagnesemia:** 6 grams (48 mEq) IM divided into two doses (3 grams each) every 12 hours for 4 doses, or 5 grams (40 mEq) in 1 liter of IV fluid infused over 3-4 hours daily. * **Eclampsia/Pre-eclampsia:** Loading dose of 4 to 6 grams IV infused over 5 to 10 minutes, followed by a maintenance infusion of 1 to 2 grams per hour. Some protocols may use IM administration. * **Torsades de Pointes:** 1 to 2 grams (8 to 16 mEq) IV as a bolus over 5 to 10 minutes, followed by 2 grams (16 mEq) diluted in 1 liter of IV fluid infused over the next hour. May repeat bolus if indicated. * **Asthma:** 2 grams (16 mEq) IV diluted in 50 mL of normal saline infused over 15 to 20 minutes. ## Pediatric Dosing * **Hypomagnesemia:** Dosing varies widely. A common regimen for severe hypomagnesemia is 25 to 50 mg/kg (0.1 to 0.2 mEq/kg) IV over 5 to 10 minutes, with a maximum of 2 grams. Maintenance infusion of 0.1 to 0.5 mEq/kg/hour. Specific protocols should be consulted. * **Eclampsia:** Pediatric dosing for eclampsia is not well-established. Consult local protocols. * **Torsades de Pointes:** 25 to 50 mg/kg (0.1 to 0.2 mEq/kg) IV over 5 to 10 minutes, maximum 2 grams. ## Dose Adjustments * **Renal Impairment:** Magnesium is primarily excreted by the kidneys. In patients with renal impairment, magnesium accumulation can occur, leading to toxicity. Dose reduction and careful monitoring are essential. Avoid use in severe renal impairment if possible. ## Contraindications * Hypermagnesemia. * Heart block. * Myocardial infarction. * Bowel obstruction or perforation. * Severe renal impairment. ## Adverse Effects * **Common:** Flushing, warmth, hypotension, nausea, vomiting, diarrhea, drowsiness, decreased deep tendon reflexes. * **Serious:** Respiratory depression, cardiac arrhythmias, cardiac arrest, coma, hypermagnesemia. ## Key Drug Interactions * **Neuromuscular blocking agents:** Magnesium can potentiate neuromuscular blockade, leading to prolonged muscle weakness or respiratory paralysis. * **Calcium:** Concurrent administration of calcium may antagonize the effects of magnesium. * **Certain antibiotics (e.g., tetracyclines, quinolones):** Magnesium can decrease the absorption of oral forms. Separate administration by at least 2-4 hours. * **Nifedipine:** Increased risk of hypotension and neuromuscular blockade. ## Monitoring * **Serum magnesium levels:** Monitor frequently, especially during IV infusions and with dose adjustments. Aim for levels between 2-4 mEq/L (1-2 mmol/L) for most indications, though higher levels may be targeted for torsades de pointes. * **Renal function (BUN, creatinine).** * **Deep tendon reflexes:** Loss of reflexes is an early sign of hypermagnesemia. * **Respiratory rate and pattern:** Monitor for signs of respiratory depression. * **Cardiac rhythm and blood pressure.** * **Urine output.** ## Clinical Pearls * Magnesium sulphate is a vesicant and should be administered cautiously to avoid extravasation. * Rapid IV administration can lead to hypotension and other adverse effects. * Always confirm the concentration of the magnesium sulphate solution being administered. * In cases of suspected hypermagnesemia, discontinue magnesium and consider calcium gluconate IV for acute symptoms. *** *This information is intended for healthcare professionals. It is essential to consult the most current prescribing information and relevant clinical guidelines for complete details, including contraindications, warnings, and adverse reactions, before making any treatment decisions.*