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# Magnesium Sulfate
## Overview
Magnesium sulfate is an essential mineral that plays a crucial role in various physiological processes, including neuromuscular function, cardiac rhythm, and enzyme activity. It is available in parenteral and oral formulations.
## Primary Indications
* **Hypomagnesemia:** Treatment and prevention of magnesium deficiency.
* **Eclampsia/Preeclampsia:** Prevention and treatment of seizures in patients with severe preeclampsia and eclampsia.
* **Torsades de Pointes:** Treatment of polymorphic ventricular tachycardia associated with a prolonged QT interval.
* **Bronchodilation:** Adjunctive therapy in severe, refractory bronchospasm in asthma or COPD.
## Adult Dosing
* **Hypomagnesemia (Symptomatic):**
* **Intravenous (IV):** 4 grams IV infused over 15-60 minutes. May be followed by a continuous infusion of 1-2 grams per hour. Dose may be adjusted based on serum magnesium levels and clinical response. Maximum infusion rate generally not to exceed 1 gram/hour to avoid hypotension.
* **Hypomagnesemia (Asymptomatic):**
* **Intramuscular (IM):** 1 gram IM every 6 hours for 4 doses.
* **Oral:** Varies widely based on product and elemental magnesium content; typically 200-400 mg elemental magnesium daily in divided doses.
* **Eclampsia/Preeclampsia:**
* **IV Loading Dose:** 4-6 grams IV over 5 minutes.
* **IV Maintenance Dose:** 1-2 grams per hour IV infusion. Local protocols may vary.
* **Torsades de Pointes:**
* **IV:** 1-2 grams IV in 10 mL D5W infused over 5-10 minutes. May be followed by an infusion of 0.5-1 gram per hour.
* **Bronchodilation (Adjunctive):**
* **IV:** 2 grams IV mixed with 100 mL normal saline or D5W infused over 20 minutes.
## Pediatric Dosing
Dosing varies significantly based on indication and weight. Specific protocols should be consulted.
* **Hypomagnesemia:**
* **IV:** 25-50 mg/kg per dose infused over 30-60 minutes. May be repeated. Maximum dose generally 1-2 grams per dose.
* **IM:** 25-50 mg/kg per dose (maximum 1 gram).
* **Eclampsia:** Limited data; consult pediatric critical care guidelines.
* **Torsades de Pointes:** 25-50 mg/kg IV (maximum 2 grams) infused over 10-20 minutes.
## Dose Adjustments
* **Renal Impairment:** Use with caution. Magnesium is renally excreted. In patients with severe renal impairment, magnesium accumulation can lead to hypermagnesemia. Monitor serum magnesium levels closely. Doses may need to be reduced.
## Contraindications
* Hypermagnesemia.
* Heart block.
* Myocardial infarction.
* Persistent hypotension.
* Myasthenia gravis (use with caution).
## Adverse Effects
* **Common:** Flushing, sweating, nausea, vomiting, hyporeflexia, hypotension, drowsiness.
* **Serious:** Respiratory depression, cardiac arrhythmias, cardiac arrest, hypermagnesemia (especially with renal impairment).
## Key Drug Interactions
* **Neuromuscular Blockers (e.g., succinylcholine, vecuronium):** Magnesium may potentiate neuromuscular blockade, increasing the risk of prolonged respiratory depression.
* **Calcium Channel Blockers:** Additive hypotensive effects and risk of cardiac arrhythmias.
* **Antibiotics (e.g., tetracyclines, quinolones):** Oral magnesium may decrease the absorption of these antibiotics by forming chelates. Separate administration by at least 2 hours.
* **Bisphosphonates:** Oral magnesium may decrease absorption. Separate administration by at least 2 hours.
## Monitoring
* **Serum Magnesium Levels:** Monitor frequently, especially during IV infusions and in patients with renal impairment. Therapeutic range for hypomagnesemia treatment is typically 2-4 mEq/L (1-2 mmol/L).
* **Renal Function:** Monitor serum creatinine and BUN.
* **Vital Signs:** Monitor blood pressure, heart rate, and respiratory rate.
* **Neurological Status:** Assess for deep tendon reflexes and respiratory effort, especially with IV administration.
* **Urine Output:** Monitor for adequate urine output (typically >0.5 mL/kg/hr) as an indicator of renal function.
## Clinical Pearls
* When treating hypomagnesemia, consider concomitant potassium and phosphate deficiencies, as they often coexist and may not correct until magnesium is replete.
* Magnesium sulfate is a calcium salt (if administered concurrently).
* In pregnant patients with preeclampsia/eclampsia, monitor for signs of magnesium toxicity, including loss of deep tendon reflexes, decreased respiratory rate (<14 breaths/min), and altered mental status. If toxicity is suspected, stop the infusion and administer calcium gluconate.
* Oral magnesium can cause diarrhea. Slow-release formulations or stool softeners may be considered.
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**Disclaimer:** This information is intended for healthcare professionals and does not replace individual clinical judgment. Always consult the most current prescribing information and relevant guidelines for definitive patient care decisions.
