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# Magnesium Sulphate
## Overview
Magnesium sulphate is a parenteral essential electrolyte used for the treatment of hypomagnesemia, life-threatening arrhythmias, and eclampsia. It acts as a calcium antagonist and reduces acetylcholine release at the neuromuscular junction.
## Primary Indications
* **Hypomagnesemia:** Severe symptomatic deficiency.
* **Obstetrics:** Prevention of seizures in eclampsia/pre-eclampsia.
* **Cardiac:** Torsades de pointes with cardiac arrest or symptomatic ventricular arrhythmia.
* **Respiratory:** Adjunctive therapy for severe acute asthma exacerbations.
## Adult Dosing
* **Hypomagnesemia (Severe):** 1–4 g IV/IM. Common regimen: 2 g IV over 15–60 minutes. May repeat as needed based on serum levels.
* **Torsades de Pointes/Cardiac Arrest:** 1–2 g IV push (over 5–20 minutes).
* **Eclampsia/Pre-eclampsia:** Loading dose 4–6 g IV over 15–20 minutes, followed by a continuous infusion of 1–2 g/hour. Follow local institutional protocols strictly.
* **Severe Asthma:** 2 g IV over 20 minutes (single dose).
## Pediatric Dosing
*(Consult specialist guidelines/PALS/local protocol as dosing varies by indication)*
* **Hypomagnesemia:** 25–50 mg/kg/dose IV/IM (max 2 g/dose). May repeat q6h for 3–4 doses.
* **Torsades de Pointes:** 25–50 mg/kg/dose IV (max 2 g/dose).
* **Asthma:** 25–50 mg/kg IV infusion (max 2 g/dose) over 20 minutes.
## Dose Adjustments
* **Renal Impairment:** Reduce dose and frequency in patients with CrCl <30 mL/min. Magnesium accumulates rapidly in renal failure; monitor serum levels closely.
## Contraindications
* Heart block (unless pacemaker present).
* Myocardial damage.
* Severe renal impairment (CrCl <20 mL/min) unless absolutely necessary.
* Hypersensitivity to the drug.
## Adverse Effects
* **Common:** Flushing, sweating, hypotension, transient bradycardia.
* **Severe (Toxicity):** Depressed deep tendon reflexes (first sign of hypermagnesemia), respiratory paralysis, complete heart block, cardiac arrest, hypocalcemia.
* **Antidote:** Calcium gluconate (1 g IV) to reverse respiratory depression/cardiac toxicity.
## Key Drug Interactions
* **Neuromuscular Blockers:** Potentiates effects; increases risk of prolonged paralysis.
* **CNS Depressants:** Enhances sedation.
* **Aminoglycosides:** Potential for increased neuromuscular blockade.
* **Digitalis Glycosides:** Use caution; sudden changes in serum magnesium levels can predispose to digoxin toxicity.
## Monitoring
* **Serum Magnesium:** Maintain therapeutic range (typically 1.7–2.3 mg/dL, though higher ranges are targeted in eclampsia).
* **Clinical Signs:** Deep tendon reflexes (patellar reflex) should be monitored hourly during continuous infusions.
* **Respiratory Rate:** Must be >12-16 breaths/min.
* **Urine Output:** Essential during eclampsia management; ensure >30 mL/hour to prevent accumulation.
## Clinical Pearls
* Rapid IV administration can cause hypotension and cardiovascular collapse.
* Magnesium sulphate is not a primary treatment for hypokalemia, but potassium replacement is often refractory to correction until concurrent hypomagnesemia is rectified.
* Always confirm availability of calcium gluconate at the bedside prior to initiating high-dose magnesium infusions for eclampsia or cardiac stabilization.
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**Educational Disclaimer:** This information is for educational purposes only. Always verify drug doses, contraindications, and compatibility with the most recent local institutional protocols, prescribing monographs, or a clinical pharmacist before administration.
