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# Magnesium Sulfate
## Overview
Magnesium sulfate is an electrolyte supplement and anticonvulsant. It acts as an NMDA receptor antagonist and calcium channel blocker, inhibiting neuromuscular transmission and reducing smooth muscle contraction.
## Primary Indications
* **Hypomagnesemia:** Replacement for deficiency.
* **Eclampsia/Pre-eclampsia:** Prevention and treatment of seizures.
* **Torsades de Pointes:** First-line treatment for cardiac arrest or symptomatic rhythms.
* **Severe Asthma:** Adjunctive therapy for acute exacerbations unresponsive to initial treatment.
## Adult Dosing
* **Hypomagnesemia:** 1–4 g IV/IM. Common regimen: 2 g IV over 10–20 minutes. Maintenance dosing varies by severity.
* **Eclampsia/Pre-eclampsia:** 4–6 g IV loading dose over 15–20 minutes, followed by 1–2 g/hour continuous infusion.
* **Torsades de Pointes:** 1–2 g IV/IO push over 5–20 minutes; may repeat once.
* **Severe Asthma:** 2 g IV infusion over 20 minutes (single dose).
## Pediatric Dosing
* **Hypomagnesemia:** 25–50 mg/kg/dose IV/IM (max 2 g/dose). May repeat q6h.
* **Asthma:** 25–75 mg/kg IV (max 2 g) infused over 20 minutes.
* *Note: Always verify protocols, as institutional pediatric guidelines vary significantly.*
## Dose Adjustments
* **Renal Impairment:** Reduce dose in patients with renal insufficiency (CrCl <30 mL/min). Monitor magnesium levels frequently; accumulation risk is high.
## Contraindications
* Heart block or myocardial damage.
* Severe renal impairment (unless as a last resort under close hemodynamic monitoring).
* Avoid IV administration within 2 hours of delivery (risk of fetal toxicity).
## Adverse Effects
* **Common:** Flushing, sensation of warmth, hypotension, bradycardia.
* **Serious:** Respiratory depression (toxicity sign), loss of deep tendon reflexes (early sign of toxicity), heart block, cardiac arrest.
* **Antidote:** Calcium gluconate (1 g IV push) for severe respiratory/cardiac toxicity.
## Key Drug Interactions
* **Neuromuscular Blockers:** Potentiates effect; risk of prolonged paralysis.
* **CNS Depressants:** Enhances sedation and respiratory depression.
* **Digoxin:** Increases risk of dig-toxicity induced rhythm disturbances if hypomagnesemia is corrected too rapidly.
## Monitoring
* **Clinical:** Check patellar reflexes (absence indicates toxic levels), respiratory rate (>12/min required), and urine output (>30 mL/hr).
* **Serum:** Magnesium levels (therapeutic range for eclampsia/seizure prophylaxis: 4–7 mg/dL). Baseline and periodic ECG for cardiac indications.
## Clinical Pearls
* **Administration:** Rapid IV push can cause profound hypotension and asystole. Reserve rapid push for cardiac arrest only.
* **Toxicity:** Loss of deep tendon reflexes is usually the first objective sign of hypermagnesemia (often seen at 7–10 mg/dL).
* **Local Policy:** Dosing for obstetric and pediatric indications is highly sensitive to institutional protocols; verify specific infusion titration orders against your hospital's policy.
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**Educational Disclaimer:** This information is for educational purposes only. Clinical practice is subject to institutional policy and local prescribing guidelines. Always verify current clinical information, contraindications, and drug-drug interactions using institutional formulary resources or authoritative clinical databases before administration.
