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# Magnesium Sulfate
## Overview
Magnesium sulfate is an essential mineral involved in numerous physiological processes, including neuromuscular function, cardiac conduction, and enzyme activity.
## Primary Indications
* Treatment of hypomagnesemia.
* Prevention and treatment of seizures in pre-eclampsia and eclampsia.
* Management of torsades de pointes.
* Bronchodilation in severe asthma exacerbations (off-label, less common).
## Adult Dosing
* **Hypomagnesemia:**
* **Severe (serum Mg < 1.5 mg/dL):** 4-6 grams IV infused over 4-24 hours. May repeat up to 10-12 grams in 24 hours.
* **Less Severe (serum Mg 1.5-2.5 mg/dL):** 2-4 grams IV infused over 1-4 hours, then 1-2 grams IV every 4-8 hours as needed.
* **Maintenance:** 4-6 grams IM every 6-12 hours or 1-2 grams IV every 4-8 hours. Dosing should be guided by serum magnesium levels.
* **Pre-eclampsia/Eclampsia:** Loading dose: 4-6 grams IV over 5-10 minutes. Maintenance infusion: 1-2 grams/hour IV. Alternatively, 5 grams IM in each buttock (using 50% solution) for a total of 10 grams, followed by 5 grams IM every 4 hours. Dosing and duration are often guided by institutional protocols.
* **Torsades de Pointes:** 1-2 grams IV in 10 mL of D5W over 5-10 minutes. May be followed by an infusion of 0.5-1 gram/hour IV.
## Pediatric Dosing
Dosing in pediatrics is less standardized and often relies on institutional protocols.
* **Hypomagnesemia:** Typically 25-50 mg/kg/dose IV infused over 5-15 minutes, not to exceed 2 grams. May be repeated every 4-12 hours. Maintenance doses depend on serum magnesium levels.
* **Eclampsia (adjunctive):** Similar to adults, but specific pediatric protocols should be consulted.
## Dose Adjustments
* **Renal Impairment:** Magnesium is renally excreted. Use with caution in renal impairment. Reduce dose and monitor serum magnesium levels closely. Avoid in severe renal failure if possible.
## Contraindications
* Hypermagnesemia.
* Heart block.
* Myocardial infarction (caution).
* Shock.
* Concomitant use of certain medications (e.g., neuromuscular blocking agents) where additive effects may be dangerous.
## Adverse Effects
* **Common:** Flushing, sweating, hypotension, nausea, vomiting, decreased reflexes, drowsiness, muscle weakness.
* **Serious:** Respiratory depression, cardiac arrhythmias, cardiac arrest, hypocalcemia, hyperkalemia.
## Key Drug Interactions
* **Neuromuscular Blocking Agents (e.g., rocuronium, vecuronium):** Magnesium sulfate can potentiate neuromuscular blockade, leading to prolonged paralysis and respiratory depression.
* **Calcium Channel Blockers:** Increased risk of hypotension and bradycardia.
* **Antibiotics (Tetracyclines, Quinolones):** Magnesium can chelate these antibiotics, reducing their absorption. Separate administration by at least 2-3 hours.
* **Digoxin:** Increased risk of digoxin toxicity with IV magnesium.
## Monitoring
* **Serum Magnesium levels:** Essential for guiding dose adjustments.
* **Renal function (BUN, creatinine):** To assess risk of accumulation.
* **Deep tendon reflexes:** Loss of reflexes indicates hypermagnesemia.
* **Respiratory rate and effort:** Monitor for respiratory depression.
* **Blood pressure and heart rate:** Monitor for hypotension and arrhythmias.
* **Urine output:** Indicator of renal perfusion.
## Clinical Pearls
* Intravenous administration should be slow and controlled to avoid adverse effects. Rapid infusion can cause flushing, hypotension, and cardiac arrhythmias.
* Intramuscular administration is painful and requires deep injection.
* Magnesium sulfate can precipitate with certain IV solutions; check compatibility.
* Monitor calcium levels in patients receiving prolonged or high-dose magnesium therapy, as it can lead to hypocalcemia.
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*Please verify current prescribing information with the official drug product labeling and institutional protocols.*
