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# Magnesium Sulfate
## Overview
Magnesium sulfate is an electrolyte used to treat or prevent hypomagnesemia and as an anticonvulsant in preeclampsia and eclampsia. It is also used as a tocolytic agent and in the management of certain cardiac arrhythmias.
## Primary Indications
* Treatment and prevention of hypomagnesemia.
* Prevention and treatment of seizures in preeclampsia and eclampsia.
* Tocolytic agent.
* Management of torsades de pointes.
## Adult Dosing
**Hypomagnesemia:**
* **Intramuscular (IM):** 1 g (8 mEq) every 6 hours for 4 doses (total 32 mEq over 24 hours).
* **Intravenous (IV):** 4 g (32 mEq) as a loading dose, followed by 1-2 g (8-16 mEq) per hour as a maintenance infusion. Dosing varies based on serum magnesium levels and renal function. A common regimen for severe hypomagnesemia is 5 g (40 mEq) in 1 L of IV fluid infused over 3 hours.
* **Oral:** Dosing varies widely; generally 200-400 mg elemental magnesium per day in divided doses.
**Preeclampsia/Eclampsia:**
* **Loading Dose (IV):** 4-6 g infused over 5-20 minutes.
* **Maintenance Dose (IV):** 1-2 g per hour. If seizures recur, an additional 2-4 g IV bolus may be administered.
* **IM:** 5 g (40 mEq) in each buttock (total 10 g) initially, followed by 5 g (40 mEq) every 4 hours.
**Torsades de Pointes:**
* **IV:** 1-2 g (8-16 mEq) diluted in 10-20 mL of D5W, infused over 5-10 minutes. May repeat every 5-15 minutes. Subsequent infusions may be given at a rate of 0.5-1 g/hour.
**Tocolytic:**
* Dosing is highly variable and institution-specific. Typically a loading dose followed by a maintenance infusion.
## Pediatric Dosing
Dosing in pediatric patients is complex and often based on weight, serum magnesium levels, and indication. Local protocols should be consulted.
**Hypomagnesemia (IV):**
* **Loading Dose:** 25-50 mg/kg (2-4 mEq/kg) infused over 30-60 minutes.
* **Maintenance Dose:** 20-30 mg/kg/day (1.6-2.4 mEq/kg/day) divided into 3-4 infusions.
**Eclampsia (IV):**
* Similar to adults, but lower doses may be used based on weight. Often 20-40 mg/kg loading dose, followed by maintenance.
## Dose Adjustments
**Renal Impairment:** Magnesium is renally excreted. Dosage reductions are necessary in patients with impaired renal function. Monitor serum magnesium levels closely. Avoid magnesium-containing medications and laxatives in patients with renal insufficiency.
## Contraindications
* Hypermagnesemia.
* Heart block.
* Myocardial infarction.
* Severe renal impairment.
* Hypersensitivity to magnesium sulfate.
## Adverse Effects
* **Common:** Flushing, sweating, hypotension, nausea, vomiting, lethargy, decreased reflexes, hypocalcemia, hypothermia.
* **Serious:** Respiratory depression, cardiac arrest, hypermagnesemia (muscle weakness, decreased deep tendon reflexes, confusion, coma, bradycardia, hypotension, cardiac arrhythmias).
## Key Drug Interactions
* **Neuromuscular Blockers:** Magnesium can potentiate the neuromuscular blocking effects of drugs like rocuronium and vecuronium.
* **Calcium Channel Blockers:** May increase risk of hypotension and bradycardia.
* **Tetracyclines and Bisphosphonates:** Oral magnesium can decrease the absorption of these agents. Separate administration by at least 2 hours.
* **Digoxin:** High doses of IV magnesium sulfate can cause digoxin toxicity.
## Monitoring
* **Serum Magnesium Levels:** Monitor frequently, especially in patients with renal impairment or receiving prolonged infusions. Therapeutic range for hypomagnesemia treatment is typically 2-4 mEq/L. Toxicity may occur above 4 mEq/L, and severe toxicity above 7 mEq/L.
* **Renal Function:** Assess baseline and monitor as needed.
* **Deep Tendon Reflexes:** Assess for signs of hypermagnesemia.
* **Respiratory Rate and Blood Pressure:** Monitor for signs of toxicity.
* **Urine Output:** Ensure adequate renal function.
## Clinical Pearls
* Magnesium sulfate is available in various concentrations; always verify the concentration to ensure correct dosing, especially for IV infusions.
* Rapid IV infusion can cause hypotension and cardiac arrhythmias.
* Hypermagnesemia can mimic hypocalcemia; monitor calcium levels if hypocalcemia is suspected or if patients are on long-term magnesium therapy.
* In acute myocardial infarction, magnesium may reduce infarct size and arrhythmias.
* Always consult institutional protocols for specific dosing regimens, particularly for tocolysis and pediatric populations, as these can vary significantly.
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**Disclaimer:** This information is intended for healthcare professionals. It is essential to consult the most current prescribing information and institutional protocols for definitive patient care decisions.
