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# Magnesium sulfate
## Overview
Magnesium sulfate is an electrolyte supplement and anticonvulsant. It acts by depressing the central nervous system and blocking peripheral neuromuscular transmission.
## Primary Indications
* **Eclampsia/Preeclampsia:** Prevention and control of seizures.
* **Torsades de Pointes:** Treatment of life-threatening ventricular arrhythmias.
* **Hypomagnesemia:** Severe symptomatic deficiency.
* **Acute Asthma:** Refractory moderate to severe exacerbations (adjunctive therapy).
## Adult Dosing
* **Eclampsia/Preeclampsia:** Loading dose of 4–6 g IV over 15–20 minutes, followed by 1–2 g/hour continuous IV infusion.
* **Torsades de Pointes/Arrhythmias:** 1–2 g IV/IO bolus over 5–20 minutes. May repeat once if needed.
* **Hypomagnesemia:** 1–4 g IV/IM. Severe deficiency may require 8–12 g over 24 hours. *Note: Dosing widely varies based on severity and local protocol; consult institution-specific guidelines.*
* **Acute Asthma:** 2 g IV over 20 minutes as a single dose.
## Pediatric Dosing
* **Hypomagnesemia:** 25–50 mg/kg/dose IV/IM; may repeat every 6 hours for 3–4 doses.
* **Acute Asthma:** 25–50 mg/kg (maximum 2 g) IV over 20–30 minutes as a single dose.
* **Arrhythmias:** 25–50 mg/kg/dose IV/IO (max 2 g).
## Dose Adjustments
* **Renal Impairment:** Requires dose reduction and increased monitoring. Magnesium is renally excreted; use with caution in patients with creatinine clearance < 30 mL/min.
## Contraindications
* Heart block.
* Myocardial damage.
* Severe renal impairment.
* Persistent use during the two hours preceding delivery (unless specifically indicated for eclampsia).
## Adverse Effects
* **Common:** Flushing, sweating, hypotension, warmth.
* **Serious:** Respiratory depression, loss of deep tendon reflexes (first sign of toxicity), cardiac arrest, hypothermia, paralysis.
## Key Drug Interactions
* **Neuromuscular Blockers:** Potentiates neuromuscular blockade.
* **CNS Depressants:** Enhances CNS depression.
* **Digoxin:** Potential for increased risk of cardiac conduction changes.
* **Aminoglycosides:** May produce excessive neuromuscular blockade.
## Monitoring
* **Serum Magnesium levels:** Maintain therapeutic range (typically 4–7 mg/dL for eclampsia; 1.7–2.3 mg/dL for maintenance).
* **Clinical Signs:** Assess deep tendon reflexes (patellar), respiratory rate (>12-16 breaths/min), and urine output (>30 mL/hr) prior to each dose.
* **Cardiac:** Monitor ECG for signs of magnesium toxicity (PR interval prolongation, QRS widening).
* **Toxicity Reversal:** Have 10% Calcium Gluconate readily available at the bedside for emergency reversal of magnesium toxicity.
## Clinical Pearls
* Rapid IV administration significantly increases the risk of hypotension and asystole.
* Magnesium sulfate is not a first-line treatment for asthma but is reserved for patients refractory to standard bronchodilators and systemic steroids.
* Always ensure the patient has adequate urine output before subsequent dosing to prevent accumulation.
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**Educational Disclaimer:** This information is for educational purposes only. Clinical practices vary by institution and patient status. Always verify current prescribing information, institutional protocols, and patient-specific factors before administration.
