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# Magnesium Sulfate
## Overview
Magnesium sulfate is an essential mineral that plays a role in numerous biochemical processes, including neuromuscular transmission and muscle contraction.
## Primary Indications
* Treatment of hypomagnesemia.
* Management of preeclampsia and eclampsia.
* Treatment of torsades de pointes.
* Management of status epilepticus refractory to first-line agents.
* Treatment of bronchospasm in severe asthma exacerbations.
## Adult Dosing
* **Hypomagnesemia:**
* **Severe (serum magnesium < 1.3 mEq/L or < 0.65 mmol/L):** 4 to 5 grams (approximately 32 to 40 mEq or 16 to 20 mmol) IV infusion over 5 to 60 minutes, followed by a continuous infusion of 1 to 2 grams per hour, or intermittent IM doses of 1 to 2 grams every 4 to 6 hours.
* **Less Severe (serum magnesium 1.3 to 1.7 mEq/L or 0.65 to 0.85 mmol/L):** 1 to 2 grams (approximately 8 to 16 mEq or 4 to 8 mmol) IV infusion over 5 to 60 minutes.
* **Preeclampsia/Eclampsia Prophylaxis/Treatment:** 4 to 6 grams IV loading dose over 5 to 20 minutes, followed by a maintenance infusion of 1 to 2 grams per hour. Dosing may vary based on local protocol.
* **Torsades de Pointes:** 1 to 2 grams (approximately 8 to 16 mEq or 4 to 8 mmol) IV in 10 mL of D5W given over 5 to 10 minutes. May repeat if necessary. May also be given as a continuous infusion of 0.5 to 1 gram per hour.
* **Status Epilepticus (Refractory):** 4 to 6 grams IV over 10 to 30 minutes. Dosing may vary based on local protocol.
* **Bronchospasm (Severe Asthma):** 2 grams IV infusion over 15 to 30 minutes.
## Pediatric Dosing
Dosing is highly variable and depends on indication, age, and weight. Often guided by institutional protocols and serum magnesium levels.
* **Hypomagnesemia:** Typically 25 to 50 mg/kg/dose IV or IM divided over 4 doses in 24 hours. Maximum single dose usually 2 grams.
* **Preeclampsia/Eclampsia (Off-label):** Dosing varies; often 20-40 mg/kg/dose IV loading, followed by 10-20 mg/kg/hr IV infusion. Consult pediatric guidelines.
* **Status Epilepticus (Refractory):** 25 to 100 mg/kg/dose IV. Dosing and maximums vary by age and institution.
* **Torsades de Pointes:** 25 to 100 mg/kg/dose IV.
## Dose Adjustments
* **Renal Impairment:** Magnesium is renally excreted. Use with caution and monitor serum magnesium levels closely in patients with renal impairment. Dose reduction is often necessary. In severe renal impairment, magnesium sulfate may be contraindicated.
## Contraindications
* Hypermagnesemia.
* Heart block.
* Myocardial infarction.
* Duchenne muscular dystrophy.
## Adverse Effects
* **Common:** Flushing, sweating, nausea, vomiting, hypotension, lethargy, decreased deep tendon reflexes.
* **Serious:** Respiratory depression, cardiac arrhythmias, cardiac arrest, neuromuscular blockade, hypermagnesemia.
## Key Drug Interactions
* **Neuromuscular blocking agents:** May potentiate neuromuscular blockade.
* **Calcium channel blockers:** Increased risk of hypotension and bradycardia.
* **Tetracyclines and bisphosphonates:** Oral magnesium sulfate can decrease absorption; separate administration by at least 2-3 hours.
## Monitoring
* Serum magnesium levels (especially during prolonged infusions or in renal impairment).
* Renal function (BUN, creatinine).
* Deep tendon reflexes.
* Respiratory rate and effort.
* Blood pressure.
* Urine output.
* ECG (if indicated).
## Clinical Pearls
* Magnesium sulfate is a potent vasodilator; administer IV infusions slowly to avoid hypotension.
* Hypermagnesemia symptoms can mimic those of calcium channel blocker overdose.
* Always check for toxicity signs (loss of reflexes, decreased respiratory rate) before administering subsequent doses.
* IV administration is preferred for rapid correction of hypomagnesemia and management of acute conditions. IM administration can be painful.
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*Please verify current prescribing information and institutional protocols before administering any medication. This information is not a substitute for professional medical advice.*
