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# Magnesium Sulfate
## Overview
Magnesium sulfate is an essential mineral that plays a vital role in numerous physiological processes, including neuromuscular function, cardiac rhythm, and enzyme activity. It is available for intravenous (IV) and intramuscular (IM) administration.
## 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 (torsades de pointes).
* **Bronchospasm:** Adjunctive therapy for severe acute asthma unresponsive to standard treatment.
* **Constipation:** Oral form (magnesium citrate) is used as a laxative. (Note: This request focuses on parenteral magnesium sulfate).
## Adult Dosing
* **Hypomagnesemia:**
* **Severe:** 4-6 g IV over 1-2 hours, followed by 1-2 g/hour IV infusion. Total daily dose typically 16-24 g IV over 24 hours.
* **Mild/Moderate:** 1-2 g IM or IV every 4-6 hours for 4 doses.
* **Eclampsia/Preeclampsia (Loading Dose):** 4-6 g IV infused over 5-10 minutes.
* **Eclampsia/Preeclampsia (Maintenance Dose):** 1-2 g/hour IV infusion. Alternatively, 5 g IM in each buttock every 4 hours. Dosing should be guided by local protocol and patient response.
* **Torsades de Pointes:** 1-2 g IV diluted in 100 mL D5W infused over 5-10 minutes. May repeat bolus, followed by infusion of 0.5-1 g/hour IV.
* **Bronchospasm:** 1-2 g IV infused over 15-20 minutes.
## Pediatric Dosing
* **Hypomagnesemia:**
* **IV:** 20-50 mg/kg/dose (max 2 g) infused over 30-60 minutes, repeated every 4-6 hours as needed.
* **IM:** 25-50 mg/kg/dose (max 2 g) every 4-6 hours.
* **Eclampsia/Preeclampsia:** Dosing varies; consult pediatric critical care guidelines.
* **Torsades de Pointes:** 25-50 mg/kg/dose (max 2 g) IV infused over 10-20 minutes.
## Dose Adjustments
* **Renal Impairment:** Magnesium is primarily excreted by the kidneys. Use with caution in patients with renal impairment. Reduce dose and monitor magnesium levels closely.
## Contraindications
* Myasthenia gravis.
* Heart block.
* Hypermagnesemia.
* Shock.
* Recent myocardial infarction (unless for torsades de pointes).
## Adverse Effects
* **Common:** Flushing, sweating, hypotension, nausea, vomiting, decreased reflexes, drowsiness.
* **Serious:** Respiratory depression, cardiac arrest, hypermagnesemia (muscle weakness, bradycardia, hypotension, cardiac arrhythmias, cardiac arrest), hyperthermia.
## Key Drug Interactions
* **Neuromuscular Blockers:** Magnesium can potentiate neuromuscular blockade.
* **Calcium Channel Blockers:** Increased risk of hypotension and bradycardia.
* **Tetracyclines and Fluoroquinolones:** Magnesium can decrease absorption; administer at least 2 hours apart.
## Monitoring
* **Serum Magnesium Levels:** Crucial, especially with prolonged infusions or renal impairment. Target levels vary by indication (e.g., 2.5-7.5 mEq/L for eclampsia).
* **Renal Function:** Monitor serum creatinine and urine output.
* **Deep Tendon Reflexes:** Loss of reflexes can indicate hypermagnesemia.
* **Respiratory Rate and Effort:** Monitor for signs of respiratory depression.
* **Blood Pressure and Heart Rate:** Monitor for hypotension and bradycardia.
* **Electrocardiogram (ECG):** For torsades de pointes and monitoring for cardiac effects.
## Clinical Pearls
* Always dilute parenteral magnesium sulfate before IV infusion. Rapid IV injection can cause flushing, sweating, and hypotension.
* Magnesium administration can cause a sensation of warmth and flushing.
* In eclampsia, monitor urine output closely; adequate output (≥ 100 mL in 4 hours) is essential for safe magnesium administration.
* Calcium gluconate or calcium chloride is the antidote for severe hypermagnesemia.
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This information is intended for healthcare professionals. Always verify current prescribing information, local protocols, and patient-specific factors before initiating treatment.
