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# Magnesium Sulfate
## Overview
Magnesium sulfate is an essential electrolyte used for life-threatening arrhythmias, eclampsia, and severe asthma. It acts as a calcium channel blocker and neuromuscular depressant.
## Primary Indications
* **Hypomagnesemia:** Replacement for symptomatic or severe deficiency.
* **Obstetric:** Prevention/treatment of seizures in eclampsia or severe preeclampsia; fetal neuroprotection in preterm labor.
* **Cardiovascular:** Torsades de pointes (TdP) with a pulse, refractory ventricular fibrillation/pulseless ventricular tachycardia.
* **Respiratory:** Adjunctive treatment in severe, acute asthma exacerbations.
## Adult Dosing
* **Torsades de Pointes (with pulse):** 1–2 g IV/IO over 5–20 minutes.
* **Hypomagnesemia (severe/symptomatic):** 1–4 g IV over 1–4 hours. Maintenance often requires 0.5–1 g/hour for 24 hours.
* **Eclampsia/Preeclampsia:** 4–6 g IV loading dose over 20 minutes, followed by 1–2 g/hour continuous infusion.
* **Severe Asthma:** 2 g IV over 20 minutes as a single dose.
## Pediatric Dosing
* **Torsades de Pointes:** 25–50 mg/kg IV/IO (max 2 g).
* **Hypomagnesemia:** 25–50 mg/kg IV per dose (max 2 g). Can repeat every 6–12 hours.
* **Severe Asthma:** 25–75 mg/kg IV (max 2 g) over 20 minutes.
## Dose Adjustments
* **Renal Impairment:** Reduce dose and frequency in patients with renal impairment (CrCl <30 mL/min). Monitor magnesium levels frequently to prevent accumulation and toxicity.
## Contraindications
* Myocardial damage (heart block).
* Severe renal failure.
* Avoid IV administration in patients with hypermagnesemia.
## Adverse Effects
* **Common:** Flushing, sweating, hypotension, transient bradycardia.
* **Serious:** Respiratory depression (first sign: loss of deep tendon reflexes), complete heart block, circulatory collapse, paralytic ileus.
## Key Drug Interactions
* **Neuromuscular Blockers:** Potentiates effect; use with extreme caution.
* **Calcium Channel Blockers:** May enhance hypotensive and neuromuscular blocking effects.
* **Digoxin:** Use caution; magnesium may exacerbate digitalis toxicity if corrected too rapidly.
## Monitoring
* **Serum Magnesium:** Target levels vary by indication (typically 2–4 mEq/L for seizure prophylaxis).
* **Clinical Safety:** Monitor vital signs (respiratory rate >12 bpm required), blood pressure, presence of deep tendon reflexes (patellar reflex is a marker for toxicity), and urine output (>0.5 mL/kg/hr).
* **Toxicity Treatment:** Keep 10% Calcium Gluconate at the bedside to reverse severe symptoms (respiratory depression).
## Clinical Pearls
* **Reflexes:** If patellar reflexes disappear, stop infusion immediately.
* **IV Push:** Never administer undiluted IV push in conscious patients due to risk of cardiac arrest and severe flushing.
* **Protocols:** Dosing for eclampsia often strictly follows local institutional "Magnesium Protocol" sets; always verify institutional guidelines.
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*Disclaimer: This information is for educational purposes only. Clinical practice guidelines frequently evolve. Always verify current prescribing information, institutional protocols, and patient-specific factors with verified drug databases (e.g., Lexicomp, Micromedex) or a pharmacist before administration.*
