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# Magnesium Sulfate
## Overview
Magnesium sulfate is an essential mineral that plays a crucial role in numerous physiological processes, including neuromuscular function, cardiac conduction, and enzyme activity. It is available in intravenous and intramuscular formulations.
## Primary Indications
* **Hypomagnesemia:** Treatment and prevention of low magnesium levels.
* **Eclampsia/Preeclampsia:** Prevention and treatment of seizures in pregnant women with severe preeclampsia or eclampsia.
* **Torsades de Pointes:** Treatment of polymorphic ventricular tachycardia associated with a prolonged QT interval.
* **Bronchospasm:** Adjunctive therapy in severe, refractory bronchospasm (e.g., asthma, COPD).
## Adult Dosing
* **Hypomagnesemia:**
* **Acute, Symptomatic:** 4-6 grams IV infused over 5-15 minutes, followed by a continuous infusion of 1-2 grams/hour.
* **Chronic/Prophylaxis:** 4 grams IM every 4-6 hours for 4 doses, or 1 gram/hour IV infusion.
* *Dosage may vary based on serum magnesium levels and patient response.*
* **Eclampsia/Preeclampsia:**
* **Loading Dose:** 4-6 grams IV infused over 5-20 minutes.
* **Maintenance Dose:** 1-2 grams/hour IV infusion.
* *Alternative: 5 grams IM in each buttock (total 10g) followed by 5g IM every 4 hours.*
* **Torsades de Pointes:**
* **Acute:** 1-2 grams IV in 10 mL of D5W or NS, infused over 5-10 minutes. May repeat once. Follow with continuous infusion of 0.5-1 gram/hour.
* **Bronchospasm (Adjunctive):**
* **Acute Severe:** 1-2 grams IV infused over 15-20 minutes.
## Pediatric Dosing
* **Hypomagnesemia:** Dosing is highly variable and should be guided by local protocols, serum magnesium levels, and patient weight. Generally, doses range from 25-50 mg/kg/dose IV or IM.
* **Eclampsia/Preeclampsia:** Not typically used in pediatric patients.
* **Torsades de Pointes:** 25-50 mg/kg IV, maximum 2 grams. Infusion rate typically over 10-20 minutes.
* **Bronchospasm (Adjunctive):** 25-50 mg/kg IV infused over 15-20 minutes, maximum 2 grams.
## Dose Adjustments
* **Renal Impairment:** Magnesium sulfate is renally excreted. Use with caution in patients with impaired renal function. Reduce dose and monitor serum magnesium levels closely. Dose adjustments are generally based on renal function (eGFR) and local protocols.
* **Hepatic Impairment:** No specific dose adjustment is typically required for hepatic impairment.
## Contraindications
* Hypermagnesemia.
* Heart block or myocardial damage (use with caution).
* Severe renal failure (use with extreme caution and dose reduction).
## Adverse Effects
* **Common:** Flushing, warmth, hypotension, diaphoresis, nausea, vomiting.
* **Serious:** Respiratory depression, loss of deep tendon reflexes, cardiac arrhythmias, CNS depression, hypermagnesemia.
## Key Drug Interactions
* **Neuromuscular Blockers:** Magnesium can potentiate neuromuscular blockade, leading to prolonged muscle weakness or paralysis.
* **Calcium Channel Blockers:** Increased risk of hypotension and cardiac depression.
* **Antibiotics (Tetracyclines, Quinolones):** Magnesium can decrease the absorption of oral tetracyclines and fluoroquinolones. Separate administration by at least 2 hours.
* **Digoxin:** High doses of magnesium may increase digoxin toxicity risk.
## Monitoring
* **Serum Magnesium Levels:** Monitor frequently, especially during infusion and with dose adjustments. Target levels vary by indication.
* **Renal Function:** Monitor BUN and creatinine.
* **Deep Tendon Reflexes:** Assess for loss of reflexes, an early sign of toxicity.
* **Respiratory Rate and Effort:** Monitor for signs of respiratory depression.
* **Blood Pressure and Heart Rate:** Monitor for hypotension and arrhythmias.
* **Urine Output:** Essential for assessing renal function.
## Clinical Pearls
* Magnesium sulfate is a central nervous system depressant.
* Always dilute before IV administration to prevent local irritation and rapid administration-related toxicity.
* Hypermagnesemia can mimic hypocalcemia.
* Discontinue infusion if deep tendon reflexes are lost, respiratory rate decreases below 16 breaths/min, or urine output is inadequate.
* Have calcium gluconate readily available as an antidote for severe magnesium toxicity.
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*Disclaimer: This information is intended for healthcare professionals and does not substitute for professional medical advice. Always consult the most current prescribing information, institutional protocols, and your knowledge base to ensure accurate and safe patient care.*
