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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 and treatment).
* Eclampsia and pre-eclampsia (seizure prophylaxis/management).
* Refractory asthma exacerbations (adjunctive therapy).
* Torsades de pointes (arrhythmia).
## Adult Dosing
* **Hypomagnesemia:** 1–4 g IV/IM. Common protocol: 1–2 g infused over 10–60 minutes. Severe cases may require 4–8 g/day in divided doses.
* **Eclampsia/Pre-eclampsia:** Loading dose 4–6 g IV over 15–20 minutes, followed by a maintenance infusion of 1–2 g/hour. Continue for 24 hours postpartum.
* **Refractory Asthma:** 2 g IV bolus over 20 minutes.
* **Torsades de pointes:** 2 g IV bolus over 5–20 minutes; may repeat once if rhythm persists.
## Pediatric Dosing
* **Hypomagnesemia:** 25–50 mg/kg/dose IV/IM q4–6h as needed.
* **Asthma:** 25–75 mg/kg IV (max 2 g) as a single dose over 20 minutes.
* *Note: Always verify pediatric dosing against weight-based institutional protocols.*
## Dose Adjustments
* **Renal Impairment:** Reduce dose in patients with renal failure. Monitor serum magnesium closely; caution if CrCl <30 mL/min. Maximum infusion rate usually 1 g/hour in patients with renal impairment.
## Contraindications
* Heart block (unless pacemaker present).
* Myocardial damage.
* Severe renal impairment (CrCl <20 mL/min) requires extreme caution/dose reduction.
* Hypermagnesemia.
## Adverse Effects
* **Common:** Flushing, sweating, hypotension, transient hypotension.
* **Serious:** Respiratory depression (early sign: loss of patellar reflexes), cardiac arrest, hypocalcemia.
* **Toxicity:** Deep tendon reflex (DTR) loss (levels >7 mg/dL), respiratory paralysis, heart block.
## Key Drug Interactions
* **Neuromuscular Blockers:** Enhanced/prolonged effect of neuromuscular blockade.
* **Aminoglycosides:** Potential for additive neuromuscular blockade.
* **CNS Depressants:** Exaggerated respiratory depression.
* **Calcium Channel Blockers:** May potentiate hypotension.
## Monitoring
* **Serum Magnesium:** Target clinical range (1.7–2.3 mg/dL for replacement; 4.8–8.4 mg/dL for eclampsia).
* **Safety Checks (for IV infusions):** Assess deep tendon reflexes (DTRs) every hour, respiratory rate (>12/min), and urine output (>30 mL/hour).
* **Antidote:** Calcium gluconate (1 g IV) should be immediately available at the bedside to treat magnesium toxicity.
## Clinical Pearls
* **Local Protocols:** Eclampsia dosing is highly protocol-dependent; verify specific institutional order sets.
* **Infusion Site:** Magnesium is irritating to veins; dilute concentrations for IV administration.
* **Hypermagnesemia:** If toxicity occurs, hold infusion and administer calcium gluconate to antagonize neuromuscular effects.
* **Renal Clearance:** Magnesium is cleared renally; frequent assessment of kidney function is critical in stable patients receiving long-term infusions.
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**Educational Disclaimer:** This information is for educational purposes only. Always verify doses, contraindications, and drug interactions against current institutional protocols, electronic health record (EHR) systems, and official prescribing information (package inserts) before administration.
