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# Magnesium Sulphate
## Overview
Magnesium sulphate is a parenteral mineral supplement and anticonvulsant. It acts as a calcium antagonist and reduces acetylcholine release at the neuromuscular junction. It undergoes renal elimination.
## Primary Indications
* **Obstetric:** Prevention/control of eclamptic seizures and neuroprotection for preterm infants at risk of cerebral palsy.
* **Cardiac:** Treatment of Torsades de Pointes (TdP) and hypomagnesemia-induced arrhythmias.
* **Metabolic:** Correction of severe hypomagnesemia.
* **Respiratory:** Adjunctive therapy for severe acute asthma exacerbations (refractory to standard therapy).
## Adult Dosing
* **Torsades de Pointes/Cardiac Arrest:** 1–2 g IV/IO over 5–20 minutes. May repeat once if needed.
* **Eclampsia (Pritchard/Zuspan):** Loading dose 4–6 g IV over 20 minutes, followed by 1–2 g/hour continuous infusion.
* **Severe Hypomagnesemia:** 1–4 g IV/IM. Dosage and rate depend on severity; typically 1–2 g over 1 hour.
* **Severe Asthma:** 2 g IV over 20 minutes.
## Pediatric Dosing
* **Hypomagnesemia:** 25–50 mg/kg/dose IV/IM (max 2 g/dose). Repeat every 6 hours as needed for 3–4 doses.
* **Asthma:** 25–50 mg/kg IV (max 2 g) administered over 15–30 minutes as a single dose.
* *Note: Dosing often dictated by local institutional protocols; confirm weight-based limits.*
## Dose Adjustments
* **Renal Impairment:** Reduce dose in patients with renal insufficiency (CrCl <30 mL/min). Monitor magnesium levels frequently. Avoid or dose reduce in severe renal failure.
## Contraindications
* Myasthenia gravis
* Hypersensitivity to magnesium
* Severe renal impairment (except in life-threatening situations)
* Heart block or myocardial damage
## Adverse Effects
* **Common:** Flushing, hypotension, bradycardia, diaphoresis, infusion site reactions.
* **Serious:** Magnesium toxicity (loss of deep tendon reflexes, respiratory depression, EKG changes: PR interval prolongation, QRS widening), cardiac arrest, coma.
## Key Drug Interactions
* **Neuromuscular Blockers:** Potentiates effect; risk of prolonged paralysis.
* **CNS Depressants:** May increase sedative effects.
* **Calcium Channel Blockers:** Increases risk of hypotension and neuromuscular blockade.
* **Digoxin:** Increased risk of digitalis toxicity if hypomagnesemia is corrected too abruptly.
## Monitoring
* **Clinical:** Respiratory rate (must be ≥12/min), urine output (>30 mL/hour), patellar reflexes (must be present).
* **Laboratory:** Serum magnesium concentrations (Target 1.5–2.5 mg/dL for routine, higher for pre-eclampsia).
* **Toxicity Markers:** If toxicity is suspected (e.g., loss of reflexes), check serum levels immediately and stop infusion.
## Clinical Pearls
* **Antidote:** Always have **Calcium Gluconate** (1 g IV) readily available to reverse respiratory depression or magnesium toxicity.
* **Asthma:** Magnesium acts as a smooth muscle relaxant; use only in patients who do not respond to initial aggressive inhaled beta-agonist therapy.
* **Administration:** Rapid IV bolus may cause profound hypotension and asystole. Reserve rapid infusion for cardiac arrest/TdP.
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*Disclaimer: This information is for educational purposes only. Dosing protocols vary by institution and patient variables. Always verify specific dosages and guidelines with your facility's drug formulary and current clinical prescribing resources before administration.*
