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# Magnesium Sulfate
## Overview
Magnesium sulfate is an essential mineral that plays a vital role in numerous enzymatic reactions, neuromuscular transmission, and cardiac function. It is available for intravenous (IV), intramuscular (IM), and oral administration.
## Primary Indications
* **Hypomagnesemia:** Treatment of low magnesium levels.
* **Eclampsia and Preeclampsia:** Prevention and treatment of seizures in pregnant women.
* **Torsades de Pointes:** Treatment of this specific type of polymorphic ventricular tachycardia.
* **Bronchospasm:** Adjunctive therapy in severe asthma or COPD exacerbations refractory to standard treatment.
* **Severe Preeclampsia/Eclampsia Prophylaxis:** Prevention of seizures in women with severe preeclampsia.
## Adult Dosing
* **Hypomagnesemia:**
* **Acute Severe:** 4-6 grams IV infused over 5-60 minutes, followed by 1-2 grams/hour IV infusion.
* **Moderate:** 1-4 grams IV or IM every 4-6 hours for 3-5 doses.
* **Oral:** 25-50 mEq (200-400 mg elemental Mg) daily in divided doses.
* **Eclampsia/Preeclampsia:**
* **Loading Dose:** 4-6 grams IV infused over 5-10 minutes.
* **Maintenance Dose:** 1-2 grams/hour IV infusion.
* **IM Dosing (alternative):** 5 grams IM in each buttock every 4 hours.
* **Torsades de Pointes:** 1-2 grams IV in 50-100 mL D5W infused over 5-10 minutes. May repeat bolus and start infusion of 0.5-1 gram/hour.
* **Bronchospasm (Adjunctive):** 1-2 grams IV infused over 15-20 minutes.
## Pediatric Dosing
* **Hypomagnesemia:**
* **IV:** 25-50 mg/kg/dose (elemental Mg) infused over 5-10 minutes. Maximum dose 2 grams. Infusion may be repeated every 4-6 hours as needed.
* **IM:** 25-50 mg/kg/dose (elemental Mg) every 4-6 hours. Maximum dose 2 grams.
* **Eclampsia/Preeclampsia:** Dosing is generally extrapolated from adult guidelines and may vary based on gestational age and institutional protocol. Typically, a loading dose of 20-40 mg/kg (elemental Mg) followed by an infusion of 1-2 grams/hour.
* **Torsades de Pointes:** 25-50 mg/kg (elemental Mg) IV infused over 10-20 minutes. May repeat. Follow with infusion of 5-10 mg/kg/hour.
## Dose Adjustments
Reduce dose in patients with impaired renal function. Monitor magnesium levels closely.
## Contraindications
* Hypermagnesemia
* Heart block
* Myocardial infarction (with caution)
* Severe renal impairment
## Adverse Effects
Common: Flushing, sweating, nausea, vomiting, decreased reflexes, hypotension.
Serious: Respiratory depression, cardiac arrest, hypermagnesemia.
## Key Drug Interactions
* **Neuromuscular Blockers:** Potentiates neuromuscular blockade.
* **Calcium Channel Blockers:** Increased risk of hypotension and bradycardia.
* **Tetracyclines and Quinolones:** May decrease absorption when administered orally concurrently; separate administration by at least 2-3 hours.
## Monitoring
* **Serum Magnesium Levels:** Essential, especially with IV or IM therapy. Target levels vary by indication (e.g., 4-7 mEq/L for eclampsia).
* **Renal Function:** Monitor creatinine and BUN.
* **Vital Signs:** Blood pressure, heart rate, respiratory rate.
* **Deep Tendon Reflexes:** Assess for loss of reflexes, an early sign of hypermagnesemia.
* **Urine Output:** Ensure adequate renal excretion.
## Clinical Pearls
* Magnesium sulfate administered IV can cause flushing and a feeling of warmth.
* Rapid IV infusion can lead to hypotension and respiratory depression.
* In IM administration, divide doses between two large muscle masses to reduce pain and risk of sterile abscess.
* IV calcium (e.g., calcium gluconate) is the antidote for severe magnesium toxicity.
**Disclaimer:** This information is intended for healthcare professionals. Always consult the most current prescribing information and relevant guidelines before administering any medication. Dosing may vary based on patient-specific factors and local institutional protocols.
