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# Magnesium Sulfate
## Overview
Magnesium sulfate is an essential mineral that plays a role in numerous biochemical reactions in the body. It is available for intravenous (IV) and intramuscular (IM) administration.
## Primary Indications
* Treatment of hypomagnesemia.
* Prevention and treatment of seizures in preeclampsia and eclampsia.
* Management of torsades de pointes.
* Treatment of status asthmaticus.
## Adult Dosing
### Hypomagnesemia
* **Severe symptomatic hypomagnesemia:** 4-5 grams (40-50 mEq or 2-2.5 mmol) of magnesium sulfate IV infused over 5-60 minutes, followed by a continuous infusion of 1-2 grams (10-20 mEq or 0.5-1 mmol) per hour. Alternatively, 1 gram (5 mEq or 0.5 mmol) IM every 6 hours for 4 doses.
* **Asymptomatic hypomagnesemia:** 1 gram (5 mEq or 0.5 mmol) IM every 6 hours for 4 doses or 1-2 grams (10-20 mEq or 0.5-1 mmol) IV infused over 5-60 minutes.
### Preeclampsia/Eclampsia
* **Loading dose:** 4-6 grams (20-30 mEq or 10-15 mmol) magnesium sulfate IV, infused over 5-20 minutes.
* **Maintenance dose:** 1-2 grams (5-10 mEq or 2.5-5 mmol) per hour IV infusion. Dose may be adjusted based on clinical response and magnesium levels. Local protocols often guide specific titration.
### Torsades de Pointes
* **With pulse:** 1-2 grams (5-10 mEq or 2.5-5 mmol) magnesium sulfate IV infused over 5-10 minutes. May be followed by infusion of 0.5-1 gram (2.5-5 mEq or 1.25-2.5 mmol) per hour.
* **Without pulse:** 2 grams (10 mEq or 5 mmol) magnesium sulfate IV as a bolus.
### Status Asthmaticus
* 1-2 grams (5-10 mEq or 2.5-5 mmol) magnesium sulfate IV infused over 15-30 minutes.
## Pediatric Dosing
Dosing in pediatrics is highly variable and often weight-based. Consult pediatric-specific guidelines or a pediatric pharmacist for precise dosing.
### Hypomagnesemia (Pediatric)
* **IV:** 25-50 mg/kg (0.1-0.2 mEq/kg or 0.05-0.1 mmol/kg) per dose infused over 10-30 minutes. Maximum single dose typically 2 grams.
* **IM:** 25-50 mg/kg per dose.
### Preeclampsia/Eclampsia (Pediatric)
* Dosing varies significantly by age and weight. Consult institutional protocols or pediatric specialists.
### Status Asthmaticus (Pediatric)
* **IV:** 25-100 mg/kg (0.1-0.4 mEq/kg or 0.05-0.2 mmol/kg) per dose infused over 15-30 minutes. Maximum single dose typically 2 grams.
## Dose Adjustments
* **Renal Impairment:** Magnesium is renally excreted. Use with caution in patients with renal impairment. Monitor magnesium levels closely and reduce the dose as necessary.
## Contraindications
* Hypermagnesemia.
* Heart block or myocardial damage (relative contraindication, use with caution).
* Hypersensitivity to magnesium sulfate.
## Adverse Effects
* **Common:** Flushing, warmth, hypotension, nausea, vomiting, drowsiness, decreased reflexes.
* **Serious:** Respiratory depression, cardiac arrest, hypermagnesemia (especially with renal impairment). Signs of hypermagnesemia include absent deep tendon reflexes, somnolence, confusion, muscle weakness, and decreased respiratory rate.
## Key Drug Interactions
* **Neuromuscular Blockers:** Magnesium can potentiolize neuromuscular blockade.
* **Calcium Channel Blockers:** Additive hypotensive effects and potential for cardiac depression.
* **Tetracyclines and Quinolones:** Magnesium can decrease the absorption of these antibiotics; administer at least 2 hours before or 4-6 hours after.
## Monitoring
* **Serum Magnesium Levels:** Essential, especially with IV infusions and in patients with renal impairment. Target levels vary by indication.
* **Renal Function:** Monitor serum creatinine and urine output.
* **Deep Tendon Reflexes:** Assess for loss of reflexes, which may indicate hypermagnesemia.
* **Respiratory Rate and Depth:** Monitor for respiratory depression.
* **Blood Pressure:** Monitor for hypotension, especially during rapid IV infusions.
* **Urine Output:** Important for assessing renal function and magnesium excretion.
## Clinical Pearls
* IV magnesium sulfate should be administered slowly to avoid hypotension and flushing.
* Rapid IV administration of magnesium sulfate can cause hypermagnesemia, CNS depression, and cardiac arrhythmias.
* When treating hypomagnesemia, correction of potassium and calcium levels may also be necessary.
* For intramuscular administration, divide the dose between two gluteal muscles to reduce pain and risk of induration.
* Ensure calcium gluconate (or calcium chloride) is readily available as an antidote for severe magnesium toxicity.
**Disclaimer:** This information is intended for healthcare professionals and is not a substitute for professional medical advice. Always consult the most current prescribing information, product monographs, and institutional protocols before administering any medication.
