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# Magnesium sulfate
## Overview
Magnesium sulfate is an essential mineral used as an electrolyte replacement, anticonvulsant, and bronchodilator. It acts by depressing the central nervous system and blocking peripheral neuromuscular transmission.
## Primary Indications
* Hypomagnesemia (prophylaxis/treatment).
* Eclampsia and severe pre-eclampsia (seizure prevention).
* Torsades de Pointes or life-threatening ventricular arrhythmias.
* Severe refractory acute asthma (adjunctive therapy).
## Adult Dosing
* **Hypomagnesemia:** 1–2 g IV/IM administered over 15–60 minutes. Severe cases may require 4–8 g over 12–24 hours.
* **Eclampsia/Pre-eclampsia:** Loading dose of 4–6 g IV over 15–30 minutes, followed by 1–2 g/hr continuous infusion.
* **Torsades de Pointes:** 1–2 g IV bolus over 5–15 minutes, may repeat once.
* **Acute Asthma:** 2 g IV over 20 minutes as a single dose.
## Pediatric Dosing
* **Hypomagnesemia:** 25–50 mg/kg/dose IV/IM (max 2 g/dose). May repeat q6h as needed.
* **Asthma:** 25–50 mg/kg (max 2 g) IV as a single dose over 20 minutes (consult institutional protocols for specific age/weight cut-offs).
## Dose Adjustments
* **Renal Impairment:** Must be cautious or avoid in severe renal failure (CrCl <30 mL/min). If necessary, do not exceed 20 g/48 hours and monitor levels frequently. Dose reduction is mandatory in renal insufficiency.
## Contraindications
* Heart block or myocardial damage.
* Severe renal impairment (CrCl <20 mL/min).
* Presence of hypermagnesemia.
## Adverse Effects
* **Common:** Flushing, sweating, hypotension, transient bradycardia.
* **Severe:** Respiratory depression, loss of deep tendon reflexes (DTRs), cardiac arrest, hypocalcemia.
## Key Drug Interactions
* **Neuromuscular Blockers:** Enhanced/prolonged effects.
* **Calcium Channel Blockers:** Risk of additive hypotension and potentiation of neuromuscular blockade.
* **Aminoglycosides:** Potential for increased neuromuscular blockade.
* **Digoxin:** Potential for increased risk of cardiac conduction abnormalities if magnesium shifts electrolytes rapidly.
## Monitoring
* **Serum Magnesium:** Maintain therapeutic range (typically 1.7–2.3 mg/dL for maintenance; 4–8 mg/dL for eclampsia).
* **Clinical Signs:** Monitor DTRs (loss of patellar reflex is an early sign of toxicity), respiratory rate (>12-16 breaths/min), and urine output (>30 mL/hr).
* **Calcium:** Monitor serum calcium as magnesium administration can affect calcium homeostasis.
## Clinical Pearls
* **Toxicity Reversal:** Keep **Calcium Gluconate (1 g IV)** at the bedside to reverse magnesium-induced respiratory depression or severe toxicity.
* **IV Administration:** Rapid IV push can lead to hypotension and cardiac arrhythmias. Infusion rate should generally not exceed 1 g/min, except in emergency cases (e.g., Torsades).
* **Eclampsia:** Dosing protocols vary significantly by institution; always adhere to institutional standing orders for maintenance infusions.
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*Disclaimer: This information is for educational purposes only. Clinical protocols vary; always verify current prescribing information, institutional guidelines, and patient-specific factors before administration.*
