Please check your internet connection and try again.
# Magnesium Sulfate
## Overview
Magnesium sulfate is an inorganic salt that acts as an electrolyte, CNS depressant, and smooth muscle relaxant. It is available in parenteral and oral formulations.
## Primary Indications
* Hypomagnesemia
* Eclampsia and severe preeclampsia (prevention and treatment)
* Torsades de Pointes
* Asthma exacerbations (adjunctive therapy)
* Constipation (oral formulation)
## Adult Dosing
* **Hypomagnesemia:**
* **Severe (serum Mg < 1.3 mg/dL):** 4-6 grams IV infused over 5-60 minutes, followed by a continuous infusion of 2-4 grams/hour for up to 24-48 hours.
* **Less Severe (serum Mg 1.3-1.7 mg/dL):** 1-2 grams IV infused over 5-60 minutes.
* **Maintenance:** Dosing varies based on serum magnesium levels and renal function, typically 4-6 grams IV daily.
* **Eclampsia/Preeclampsia:** 4-6 grams IV loading dose over 5-20 minutes, followed by a continuous infusion of 1-2 grams/hour. Alternatively, IM dosing can be used (e.g., 5g IM in each buttock initially, then 5g IM every 4 hours). Protocols vary significantly by institution.
* **Torsades de Pointes:** 1-2 grams IV in 50-100 mL D5W over 5-10 minutes. Repeat doses may be administered. For ongoing treatment, a continuous infusion of 0.5-1 gram/hour may be used.
* **Asthma Exacerbations:** 1-2 grams IV infused over 15-30 minutes.
* **Constipation (Oral):** Magnesium citrate solution (e.g., 10 oz bottle) or milk of magnesia (30-60 mL). Onset is typically 30 minutes to 6 hours.
## Pediatric Dosing
Dosing is highly variable and often based on institutional protocols.
* **Hypomagnesemia:** Typically 25-50 mg/kg/dose IV over 10-30 minutes, not to exceed 2 grams. Doses may be repeated every 12-24 hours. Maintenance infusion: 20-30 mg/kg/hour.
* **Eclampsia/Preeclampsia:** Similar to adults, but dosing adjusted for weight.
* **Asthma Exacerbations:** Typically 25-50 mg/kg IV infused over 15-30 minutes, not to exceed 2 grams.
## Dose Adjustments
* **Renal Impairment:** Magnesium is renally excreted. Use with caution in patients with renal impairment. Reduced doses and increased monitoring of serum magnesium levels are necessary. Avoid in severe renal failure if possible.
## Contraindications
* Hypermagnesemia
* Heart block greater than first degree
* Myocardial infarction (if hyperkalemic)
* Myocardial conduction abnormalities
* Severe renal dysfunction
* Intestinal obstruction (for oral preparations)
* Rectal impaction (for oral preparations)
## Adverse Effects
* **Common:** Flushing, sweating, hypotension, hypothermia, nausea, vomiting, decreased deep tendon reflexes, drowsiness, muscle weakness.
* **Serious:** Respiratory depression, cardiac arrest, hypermagnesemia (neuromuscular blockade, absent reflexes, ECG changes, cardiovascular collapse).
## Key Drug Interactions
* **Calcium Salts:** May antagonize the cardiac and CNS depressant effects of magnesium.
* **Neuromuscular Blockers (e.g., rocuronium, vecuronium):** Magnesium can potentiate neuromuscular blockade, leading to prolonged paralysis.
* **Digoxin:** IV magnesium can potentially exacerbate digoxin toxicity by increasing myocardial contractility.
* **Tetracyclines and Fluoroquinolones:** Oral magnesium can decrease the absorption of these antibiotics by forming insoluble complexes. Separate administration by at least 2-4 hours.
## Monitoring
* **Serum Magnesium Levels:** Monitor regularly, especially during continuous infusions or in patients with renal impairment. Therapeutic levels for hypomagnesemia are generally 2-3.5 mg/dL. Levels above 4 mg/dL can cause adverse effects.
* **Renal Function:** Monitor serum creatinine and BUN.
* **Vital Signs:** Blood pressure, heart rate, respiratory rate.
* **Deep Tendon Reflexes:** Assess for loss of reflexes, an early sign of hypermagnesemia.
* **Urine Output:** Monitor for adequacy of renal function.
* **ECG:** Especially in patients receiving high doses or with risk factors for cardiac issues.
## Clinical Pearls
* Magnesium sulfate is a vesicant; infuse through a central line if possible, especially with higher concentrations or prolonged infusions. Dilute appropriately.
* Rapid IV infusion can cause hypotension and flushing.
* Oral magnesium sulfate can cause diarrhea.
* In eclampsia, monitor for seizure recurrence and signs of magnesium toxicity. Have IV calcium gluconate readily available as an antidote for magnesium toxicity.
* For Torsades de Pointes, magnesium is effective regardless of the patient's baseline magnesium level.
***
*This information is intended as a quick reference and does not replace the need to consult the official prescribing information and institutional protocols. Always verify current drug information before administration.*
