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# Magnesium Sulfate
## Overview
Magnesium sulfate is an electrolyte that plays a role in numerous biochemical reactions. It is administered for various medical conditions, primarily related to magnesium deficiency and obstetric emergencies.
## Primary Indications
* Treatment of hypomagnesemia.
* Prevention and treatment of seizures in preeclampsia and eclampsia.
* Management of status epilepticus refractory to other treatments.
* Bronchodilator in acute severe asthma exacerbations.
* Tocolytic agent to inhibit preterm labor.
## Adult Dosing
* **Hypomagnesemia (Symptomatic):**
* Initial IV bolus: 4-5 grams of magnesium sulfate (20-40 mEq) infused over 5-20 minutes.
* Maintenance IV infusion: 1-2 grams of magnesium sulfate (8-16 mEq) per hour, adjusted based on serum magnesium levels and clinical response. Total daily dose typically 20-40 grams.
* IM injection: 1 gram (8 mEq) every 4 hours for 4 doses if IV access is not feasible.
* **Preeclampsia/Eclampsia Prophylaxis/Treatment:**
* Loading dose IV: 4-6 grams of magnesium sulfate infused over 15-20 minutes.
* Maintenance infusion IV: 1-2 grams per hour.
* Alternative IM: 5 grams of magnesium sulfate in each buttock (total 10 grams) every 4 hours.
* **Status Epilepticus (Adjunctive):**
* IV infusion: 1-2 grams of magnesium sulfate diluted in 50-100 mL of D5W or normal saline, infused over 10-20 minutes.
* **Asthma (Severe Exacerbation):**
* IV infusion: 1-2 grams of magnesium sulfate diluted in 50-100 mL of normal saline, infused over 15-30 minutes.
* **Tocolysis (Preterm Labor):**
* Loading dose IV: 4-6 grams of magnesium sulfate infused over 20-30 minutes.
* Maintenance infusion IV: 1-2 grams per hour. Dosing and duration are highly variable and dependent on local protocols and clinical response.
## Pediatric Dosing
Dosing in pediatric patients is often weight-based and may vary significantly based on the indication and institutional protocols. Consultation with a pediatric specialist or pharmacist is recommended.
* **Hypomagnesemia (IV):**
* Initial: 25-50 mg/kg (0.1-0.2 mEq/kg) per dose infused over 10 minutes, may repeat every 4-12 hours.
* Maintenance: 20-30 mg/kg/hour (0.08-0.12 mEq/kg/hour) infusion.
* **Eclampsia (IV):**
* Loading dose: 25-50 mg/kg (0.1-0.2 mEq/kg) per dose infused over 10 minutes, not to exceed 2 grams.
* Maintenance infusion: 10-15 mg/kg/hour (0.04-0.06 mEq/kg/hour), not to exceed 1 gram/hour.
* **Asthma (Severe Exacerbation, IV):**
* 25-50 mg/kg (0.1-0.2 mEq/kg) per dose infused over 15-30 minutes, maximum 2 grams.
## Dose Adjustments
* **Renal Impairment:** Magnesium sulfate is renally excreted. Use with caution and reduce dose in patients with impaired renal function. Monitor serum magnesium levels closely. Significant dose reduction may be necessary in severe renal impairment.
## Contraindications
* Hypermagnesemia.
* Hypocalcemia.
* Heart block.
* Myocardial infarction.
* Severe renal impairment.
* Anuria.
## Adverse Effects
Common: Flushing, hypotension, somnolence, nausea, vomiting.
Serious: Respiratory depression, cardiac arrest, absent deep tendon reflexes, hyperreflexia, muscle weakness, decreased urine output, diaphoresis.
## Key Drug Interactions
* **Neuromuscular Blockers (e.g., succinylcholine, vecuronium):** Magnesium sulfate can potentiate neuromuscular blockade, leading to prolonged respiratory depression.
* **Calcium Channel Blockers:** Additive hypotensive effects and risk of severe hypotension.
* **Digitalis Glycosides:** Hypermagnesemia can precipitate digitalis toxicity.
## Monitoring
* **Serum Magnesium Levels:** Monitor frequently, especially during IV infusions and in patients with renal impairment. Therapeutic range is typically 2.0-3.5 mEq/L for treatment of eclampsia and 1.7-2.2 mEq/L for hypomagnesemia.
* **Vital Signs:** Blood pressure, heart rate, respiratory rate.
* **Deep Tendon Reflexes:** Assess for loss of reflexes, which indicates magnesium toxicity.
* **Urine Output:** Monitor for adequate renal function.
* **Electrocardiogram (ECG):** Assess for cardiac effects.
## Clinical Pearls
* Magnesium sulfate administration can cause flushing and diaphoresis.
* Withhold magnesium sulfate if deep tendon reflexes are absent, respiratory rate is less than 12 breaths/minute, or urine output is less than 100 mL in the preceding 4 hours (in adults).
* Calcium gluconate or calcium chloride is the antidote for magnesium toxicity.
* Administration of IV magnesium sulfate can cause hypotension; administer infusions slowly and monitor blood pressure.
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**Disclaimer:** This information is intended for healthcare professionals. Always consult the current official prescribing information and relevant guidelines for complete and up-to-date details before making any clinical decisions.
