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# Magnesium Sulfate
## Overview
Magnesium sulfate is an essential mineral used for treating hypomagnesemia, preeclampsia/eclampsia, and as an adjunct in severe asthma or arrhythmias. It acts as a calcium antagonist and CNS depressant.
## Primary Indications
* **Obstetrics:** Prevention/control of seizures in preeclampsia and eclampsia.
* **Cardiac:** Torsades de pointes with a pulse; refractory ventricular arrhythmias (hypomagnesemia-associated).
* **Metabolic:** Acute hypomagnesemia.
* **Pulmonary:** Adjunctive therapy for severe acute asthma (refractory cases).
## Adult Dosing
* **Hypomagnesemia (Mild):** 1–2 g IM or IV (slowly over 1 hour).
* **Hypomagnesemia (Severe/Symptomatic):** 1–4 g IV over 5–60 minutes; may repeat. Do not exceed 8 g/24 hours for asymptomatic patients.
* **Torsades de Pointes:** 1–2 g IV push over 5–20 minutes.
* **Eclampsia/Preeclampsia:** 4–6 g IV loading dose over 15–20 minutes, followed by a continuous infusion of 1–2 g/hour.
* **Severe Asthma:** 2 g IV administered over 20 minutes (single dose).
## Pediatric Dosing
* **Hypomagnesemia:** 25–50 mg/kg/dose IV (max 2 g/dose) every 4–6 hours for 3–4 doses.
* **Asthma:** 25–75 mg/kg IV (max 2 g) administered as a single dose over 20–30 minutes.
* **Torsades de Pointes:** 25–50 mg/kg IV (max 2 g).
## Dose Adjustments
* **Renal Impairment:** Reduce dose by 50% in patients with CrCl < 30 mL/min or elevated serum creatinine. Magnesium is renally cleared; accumulation poses high risk of toxicity.
## Contraindications
* Myocardial damage or heart block.
* Severe renal impairment (CrCl < 20 mL/min).
* Avoid use within 2 hours of delivery if possible.
## Adverse Effects
* **Common:** Flushing, sweating, hypotension (rapid infusion), bradycardia.
* **Toxicity:** Loss of deep tendon reflexes (first sign of toxicity), respiratory depression (paralysis), cardiac arrest, hypocalcemia.
* **Antidote:** Calcium gluconate (1 g IV) to reverse respiratory depression/cardiac toxicity.
## Key Drug Interactions
* **Neuromuscular Blockers:** Potentiates effect; risk of prolonged paralysis.
* **CNS Depressants:** Enhances sedation.
* **Aminoglycosides:** Potential for additive neuromuscular blockade.
* **Calcium Channel Blockers:** Risk of profound hypotension.
## Monitoring
* **Reflexes:** Check patellar reflexes hourly; absence indicates toxicity.
* **Respiratory:** Monitor RR (maintain > 12–16 breaths/min).
* **Cardiac:** Continuous ECG monitoring in acute settings.
* **Labs:** Serum magnesium levels periodically (target 1.7–2.3 mg/dL).
* **Urine Output:** Maintain ≥ 30 mL/hour during infusion.
## Clinical Pearls
* **Administration:** Rapid IV push can cause cardiac arrest; always administer via infusion pump.
* **Local Protocols:** Eclampsia management protocols vary significantly by institution; strictly adhere to facility-specific guidelines for OB maintenance dosing.
* **Extravasation:** Ensure site is patent; magnesium is a tissue irritant.
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*Disclaimer: This information is for educational purposes only. Clinical guidelines and local hospital protocols may vary. Always verify current prescribing information, dosing, and compatibility via institutional resources and formal drug references before administration.*
