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# Magnesium Sulphate
## Overview
Magnesium sulphate is a parenteral essential electrolyte and anticonvulsant. It acts as a physiological calcium antagonist, inhibiting neuromuscular transmission and exerting sedative and anticonvulsant effects.
## Primary Indications
* **Eclampsia/Pre-eclampsia:** Seizure prophylaxis and treatment.
* **Torsades de Pointes:** Management of life-threatening cardiac arrhythmias.
* **Severe Asthma:** Adjunctive therapy for acute exacerbations.
* **Hypomagnesemia:** Severe deficiency.
* **Preterm Labor:** Neuroprotection (fetal/neonatal).
## Adult Dosing
* **Eclampsia/Pre-eclampsia:** Loading dose 4–6 g IV over 15–20 minutes, followed by maintenance 1–2 g/hour by continuous IV infusion.
* **Torsades de Pointes:** 1–2 g IV push (diluted) over 5–20 minutes; may repeat once if necessary.
* **Severe Acute Asthma:** 2 g IV over 20 minutes as a single dose.
* **Hypomagnesemia:** 1–4 g IV/IM. Severe depletion may require 1 g/hour infusion; avoid clinical toxicity.
## Pediatric Dosing
* **Asthma:** 25–50 mg/kg (max 2 g) IV over 20 minutes.
* **Hypomagnesemia:** 25–50 mg/kg/dose IV/IM every 6 hours for 3–4 doses.
* **Cardiac Arrest (Torsades):** 25–50 mg/kg IV bolus (max 2 g).
## Dose Adjustments
* **Renal Impairment:** Reduce dose and frequency in patients with CrCl <30 mL/min. Magnesium is renally excreted; monitor serum levels closely to avoid toxicity.
* **Elderly:** Use lower end of dosing range; increased sensitivity to CNS suppression.
## Contraindications
* Myasthenia gravis.
* Heart block or myocardial damage (significant).
* Presence of hypermagnesemia.
* Anuria/severe renal impairment.
## Adverse Effects
* **Dose-dependent toxicity:** Loss of deep tendon reflexes (first sign of toxicity), respiratory depression, hypotension, flushing, bradycardia, lethargy, and cardiac arrest.
* **Antidote:** Calcium gluconate 1 g IV should be immediately available at the bedside for suspected toxicity.
## Key Drug Interactions
* **CNS Depressants:** Enhanced sedative effects.
* **Neuromuscular Blockers:** Potentiates neuromuscular blockade.
* **Aminoglycosides:** Potential for increased risk of respiratory paralysis.
* **Digoxin:** Use with caution; may precipitate serious conduction disturbances if magnesium is given rapidly.
## Monitoring
* **Clinical:** Check patellar reflexes (DTRs), respiratory rate (>12-16 breaths/min), and urine output (>30 mL/hour).
* **Laboratory:** Serum magnesium levels (Therapeutic range for eclampsia: 4–8 mg/dL; 2–4 mmol/L).
* **ECG:** Monitor for PR/QRS interval prolongation during rapid infusions.
## Clinical Pearls
* **Extravasation:** High risk; infuse via large vein.
* **Institutional Protocols:** Dosing for eclampsia often strictly follows facility-specific protocols (e.g., Zuspan regimen); always consult your local obstetric or ICU guidelines.
* **Hydration:** Ensure adequate renal function prior to administration.
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**Disclaimer:** This information is intended for educational purposes for healthcare professionals and must be verified against current institutional policies, local prescribing information, and the patient's specific clinical context. Always consult the latest drug monographs.
