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# Magnesium sulphate
## Overview
Magnesium sulphate is an essential electrolyte used for its anticonvulsant, antiarrhythmic, and tocolytic properties. It acts as a physiological calcium antagonist and neuromuscular blocker.
## Primary Indications
* **Eclampsia/Pre-eclampsia:** Seizure prophylaxis and treatment.
* **Torsades de Pointes:** Immediate management of polymorphic ventricular tachycardia associated with long QT interval.
* **Severe Asthma:** Adjunctive therapy for acute exacerbations unresponsive to bronchodilators/steroids.
* **Hypomagnesaemia:** Symptomatic or severe deficiency.
## Adult Dosing
* **Eclampsia:** 4–6 g IV loading dose over 15–20 minutes, followed by 1–2 g/hour continuous infusion.
* **Torsades de Pointes/Cardiac Arrest:** 1–2 g IV/IO bolus over 5–20 minutes.
* **Severe Asthma:** 2 g IV over 20 minutes (single dose).
* **Hypomagnesaemia:** 1–4 g IV/IM, titrated based on serum levels. Max 12 g/24 hours for severe deficiency.
## Pediatric Dosing
* **Asthma:** 25–75 mg/kg (max 2 g) IV infused over 20–30 minutes.
* **Hypomagnesaemia:** 25–50 mg/kg/dose IV/IM every 6 hours as needed.
* *Note:* Pediatric dosing is highly protocol-dependent; verify with pediatric-specific institutional guidelines (e.g., PALS/standardized formularies).
## Dose Adjustments
* **Renal Impairment:** Reduce dose in patients with CrCl < 30 mL/min. Magnesium is renally excreted; monitor closely for accumulation and toxicity.
## Contraindications
* Heart block (unless pacemaker present).
* Myocardial damage.
* Severe renal impairment (Relative contraindication; requires extreme caution).
* Hypocalcaemia (correct first, if possible).
## Adverse Effects
* **Common:** Flushing, sweating, hypotension, transient bradycardia.
* **Severe (Toxicity):** Loss of deep tendon reflexes (early sign), respiratory depression, cardiac arrest, AV block.
## Key Drug Interactions
* **Neuromuscular Blockers:** Potentiates effect; risk of prolonged paralysis.
* **CNS Depressants:** May increase sedative/depressant effects.
* **Calcium Channel Blockers:** Increased risk of severe hypotension and neuromuscular blockade.
* **Digoxin:** Increased risk of arrhythmias if accompanied by hypomagnesaemia.
## Monitoring
* **Clinical:** Assess deep tendon reflexes (DTRs), respiratory rate (>12-16 bpm), and urine output (>0.5 mL/kg/hr) hourly during continuous infusion.
* **Laboratory:** Serum magnesium levels periodically. Normal range: 1.7–2.2 mg/dL (0.85–1.1 mmol/L).
* **Antidote:** Calcium gluconate (1 g IV) should be readily available at the bedside to reverse respiratory depression/toxicity.
## Clinical Pearls
* **Toxicity signs:** Loss of patellar reflex often precedes respiratory paralysis.
* **Administration:** Slow IV administration is critical in non-arrest settings to avoid hypotension and asystole.
* **Local Protocols:** Institutional protocols for eclampsia or asthma vary significantly; always confirm infusion rates and concentration requirements with local clinical pathways.
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**Educational Disclaimer:** This information is for educational purposes only and does not replace professional medical judgment or institutional policies. Always verify specific doses, contraindications, and administration protocols using primary drug references (e.g., Lexicomp, Micromedex, or local hospital formulary) before prescribing or administering medication.
