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# Magnesium Sulphate
## Overview
Magnesium sulphate is a parenteral mineral supplement and anticonvulsant. It acts as a calcium channel blocker at the neuromuscular junction and the central nervous system. Clinical effects are dependent on the titration of serum concentrations.
## Primary Indications
* **Eclampsia/Preeclampsia:** Prevention and control of seizures.
* **Life-threatening Torsades de Pointes:** Cardiac arrhythmia management.
* **Severe Hypomagnesemia:** Symptomatic replacement.
* **Asthma:** Adjunct for severe, refractory exacerbations.
## Adult Dosing
* **Eclampsia/Preeclampsia:** 4–6 g IV bolus over 15–20 minutes, followed by 1–2 g/hour continuous infusion. Duration determined by local protocols (typically 24 hours postpartum).
* **Torsades de Pointes:** 1–2 g IV/IO bolus over 5–20 minutes. May repeat or follow with infusion (0.5–1 g/hour) for recurring episodes.
* **Hypomagnesemia:** 1–2 g IV over 15–60 minutes. Severe symptomatic cases may require up to 4–8 g over 12–24 hours.
* **Severe Asthma:** 2 g IV over 20 minutes (single dose).
## Pediatric Dosing
* **Status Asthmaticus:** 25–50 mg/kg (maximum 2 g) IV administered over 20–30 minutes.
* **Hypomagnesemia:** 25–50 mg/kg/dose IV every 6–12 hours for 3–4 doses; may be repeated based on serum levels.
* *Note: Always verify paediatric doses against weight-based institutional formularies.*
## 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
* Hypersensitivity to magnesium.
* Heart block or significant myocardial damage.
* Severe renal impairment (unless dialysis is available).
* Avoid IV administration within 2 hours of delivery for eclampsia treatment (if possible) to prevent neonatal respiratory depression.
## Adverse Effects
* **Common:** Flushing, hypotension, bradycardia, sedation.
* **Serious (Magnesium Toxicity):** Loss of deep tendon reflexes (first sign of toxicity), respiratory depression, cardiac arrest, AV block.
## Key Drug Interactions
* **Neuromuscular Blockers:** Potentiates effect; risk of prolonged paralysis.
* **Aminoglycosides/Calcium Channel Blockers:** May enhance neuromuscular blockade or hypotension.
* **Digoxin:** Rapid infusion may increase risk of arrhythmias; monitor closely.
## Monitoring
* **Clinical:** Assess patellar reflexes, respiratory rate (>12-16 breaths/min), and urine output (>30 mL/hour).
* **Laboratory:** Serum magnesium concentrations (Therapeutic range: 4–7 mEq/L or 2–3.5 mmol/L for eclampsia; 1.7–2.3 mg/dL for maintenance).
* **Toxicity Management:** Keep **Calcium Gluconate (1 g IV)** at the bedside as an antidote for magnesium toxicity.
## Clinical Pearls
* **Administration:** Rapid IV bolus can cause profound hypotension and asystole.
* **Monitoring Trough:** In patients with renal failure, obtain magnesium levels before every subsequent dose.
* **Reflexes:** The disappearance of the patellar reflex usually occurs at serum concentrations of 7–10 mEq/L; respiratory paralysis occurs at >10 mEq/L.
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**Educational Disclaimer:** This information is for educational purposes only. Clinical protocols for dosing, especially in obstetrics and pediatrics, vary significantly by institution. Verify all doses against current, facility-specific clinical guidelines and the patient’s renal/cardiac status before prescribing or administering.
