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# Magnesium Sulfate
## Overview
Magnesium sulfate is an inorganic salt that acts as a mineral supplement and an anticonvulsant. It plays a role in numerous enzymatic reactions and neuromuscular transmission.
## Primary Indications
* Treatment of hypomagnesemia
* Management of pre-eclampsia and eclampsia
* Prevention and treatment of seizures in specific conditions (e.g., eclampsia, status epilepticus in pediatric patients)
* Treatment of torsades de pointes
* Bronchodilation in severe asthma exacerbations
## Adult Dosing
* **Hypomagnesemia:**
* Severe deficiency: 4-5 grams IV infused over 15-30 minutes, followed by 1-2 grams per hour as a continuous infusion.
* Less severe deficiency: 1 gram IM every 6 hours for 4 doses, or 1 gram IV every 12 hours.
* **Pre-eclampsia/Eclampsia:** Loading dose: 4-6 grams IV infused over 5-10 minutes. Maintenance infusion: 1-2 grams per hour. Dose may be adjusted based on clinical response and magnesium levels. Alternative IM dosing exists (e.g., 5 grams IM in each buttock, followed by 5 grams IM every 4 hours).
* **Torsades de Pointes:** 1-2 grams IV in 50-100 mL D5W over 5-10 minutes. May repeat if necessary. Continuous infusion of 0.5-1 gram per hour may be considered.
* **Asthma (Severe Exacerbations):** 1-2 grams IV diluted in 50-100 mL normal saline infused over 15-30 minutes.
## Pediatric Dosing
* **Hypomagnesemia:** Dosing varies significantly by age and weight. A common guideline is 25-50 mg/kg/dose IV every 4-6 hours, with a maximum dose of 2 grams per dose. Maintenance infusion rates are typically 0.5-1 mmol/kg/hour (approximately 12-24 mg/kg/hour). Specific protocols are essential.
* **Eclampsia:** Often follows adult protocols but may be adjusted based on size.
* **Status Epilepticus:** 25-50 mg/kg/dose IV infused over 10-20 minutes, not to exceed 2 grams per dose. May be repeated.
* **Torsades de Pointes:** 25-50 mg/kg IV infused over 10-20 minutes, not to exceed 2 grams per dose. Continuous infusion may follow.
## Dose Adjustments
Reduce dose and frequency in patients with impaired renal function. In severe renal impairment, magnesium sulfate may be contraindicated.
## Contraindications
* Hypermagnesemia
* Heart block
* Myocardial infarction (in the setting of acute MI, caution is advised)
* Hypersensitivity to magnesium sulfate
## Adverse Effects
Common: Flushing, hypotension, nausea, vomiting, drowsiness, decreased deep tendon reflexes.
Serious: Respiratory depression, cardiac arrest, hypermagnesemia, hypothermia, decreased urine output.
## Key Drug Interactions
* **Nondepolarizing Neuromuscular Blockers:** Magnesium can potentiate neuromuscular blockade, requiring reduced doses of these agents.
* **Calcium Channel Blockers:** Additive myocardial depression and hypotension.
* **Antibiotics (Tetracyclines, Quinolones):** Magnesium can impair absorption; administer these agents at least 2 hours before or 4-6 hours after magnesium.
* **Digoxin:** Increased risk of digoxin toxicity and AV block.
## Monitoring
* Serum magnesium levels (aim for therapeutic range based on indication, often 2-3.5 mEq/L for eclampsia)
* Renal function (BUN, creatinine, urine output)
* Deep tendon reflexes (loss of reflexes indicates toxicity)
* Respiratory rate and depth
* Blood pressure
* Cardiac rhythm (ECG)
## Clinical Pearls
* Rapid IV infusion can cause hypotension, flushing, and cardiac arrhythmias. Infuse slowly and monitor vital signs closely.
* Loss of deep tendon reflexes is an early sign of magnesium toxicity.
* Calcium gluconate (1 gram IV) is the antidote for severe magnesium toxicity.
* Ensure adequate hydration and urinary output during magnesium therapy.
* Dosing in neonates and infants requires extreme caution and adherence to specific protocols due to immature renal function.
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*Please verify current prescribing information and institutional protocols before administration.*
