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# Magnesium Sulfate
## Overview
Magnesium sulfate is an essential mineral that plays a crucial role in numerous biochemical reactions within the body, including neuromuscular transmission, cardiac excitability, and protein synthesis. It can be administered intravenously (IV) or intramuscularly (IM).
## Primary Indications
* **Hypomagnesemia:** Treatment of magnesium deficiency.
* **Eclampsia/Preeclampsia:** Prevention and treatment of seizures associated with severe preeclampsia and eclampsia.
* **Torsades de Pointes:** Treatment of polymorphic ventricular tachycardia with a prolonged QT interval.
* **Bronchodilator:** Adjunctive therapy in severe bronchospasm (e.g., asthma).
* **Anticonvulsant:** Adjunctive therapy for status epilepticus.
## Adult Dosing
* **Hypomagnesemia:**
* **Severe (serum Mg < 1.3 mg/dL):** Loading dose: 4-6 grams IV over 5-60 minutes. Maintenance dose: 1-2 grams per hour IV, adjusted based on serum magnesium levels and clinical response. Alternatively, 1 gram IM every 4 hours for 4 doses.
* **Mild/Moderate (serum Mg 1.3-2.1 mg/dL):** 1-2 grams IV or IM over 1-2 hours.
* **Eclampsia/Preeclampsia:**
* **Loading Dose:** 4-6 grams IV infused over 5-10 minutes.
* **Maintenance Dose:** 1-2 grams per hour IV infusion. Dosing may be adjusted based on local protocols and patient response.
* **Torsades de Pointes:** 1-2 grams IV in 50-100 mL D5W over 5-10 minutes. Further doses of 2 grams IV every 15-30 minutes if needed.
* **Bronchodilator (Adjunctive):** 1-2 grams IV infused over 15-30 minutes.
* **Status Epilepticus (Adjunctive):** 1-2 grams IV infused over 10-20 minutes.
Maximum daily IV dose is generally not well-defined and depends on indication and renal function.
## Pediatric Dosing
Dosing is highly variable and depends on indication, weight, and serum magnesium levels. Local protocols should be consulted.
* **Hypomagnesemia:** Loading dose: 25-50 mg/kg (0.1-0.2 mmol/kg) IV over 30-60 minutes. Maintenance dose: 20-30 mg/kg/day (0.08-0.12 mmol/kg/day) IV, divided every 6-12 hours. IM administration can also be used. Maximum single IV dose generally not to exceed 1 gram.
## Dose Adjustments
* **Renal Impairment:** Magnesium is renally excreted. In patients with impaired renal function, doses should be reduced and magnesium levels closely monitored to prevent accumulation and hypermagnesemia. Avoid if creatinine clearance is less than 30 mL/min.
## Contraindications
* Hypermagnesemia.
* Heart block.
* Myocardial infarction.
* Severe renal impairment (contraindicated for maintenance therapy).
## Adverse Effects
* **Common:** Flushing, warmth, hypotension, diaphoresis, nausea, vomiting.
* **Serious:** Respiratory depression, cardiac arrest, loss of deep tendon reflexes, somnolence, confusion, muscle weakness, hypocalcemia, hyperkalemia.
## Key Drug Interactions
* **Neuromuscular Blockers:** Magnesium can potentiate the effects of neuromuscular blocking agents, leading to prolonged muscle paralysis.
* **Calcium:** Calcium administration can antagonize the effects of magnesium.
* **Tetracyclines and Fluoroquinolones:** Magnesium can decrease the absorption of these antibiotics when administered orally. Separate administration by at least 2 hours.
## Monitoring
* **Serum Magnesium Levels:** Essential for guiding therapy and preventing toxicity, especially with prolonged infusions or impaired renal function. Target levels vary by indication.
* **Renal Function:** Monitor BUN, creatinine, and urine output.
* **Vital Signs:** Blood pressure, heart rate, respiratory rate.
* **Deep Tendon Reflexes:** Loss of reflexes is an early sign of hypermagnesemia.
* **Electrocardiogram (ECG):** Especially in Torsades de Pointes treatment or if cardiac effects are suspected.
* **Urine Output:** Adequate urine output is necessary for magnesium excretion.
## Clinical Pearls
* Rapid IV infusion can cause hypotension, flushing, and cardiac arrhythmias. Infuse as recommended.
* Magnesium sulfate is a CNS depressant. Monitor for signs of toxicity like somnolence and loss of reflexes.
* In patients with Torsades de Pointes, consider IV calcium if hypocalcemia is also present.
* For hypomagnesemia, IM injections can be painful and should be given deep into a large muscle with adequate aspiration.
**Disclaimer:** This information is intended for healthcare professionals. Always consult the most current prescribing information and relevant institutional protocols for complete details and to ensure patient safety.
