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# Magnesium Sulfate
## Overview
Magnesium sulfate is an essential mineral that plays a role in numerous biochemical reactions. It is administered parenterally for specific medical conditions.
## Primary Indications
* Treatment of hypomagnesemia.
* Prevention and treatment of eclampsia in pregnant patients.
* Management of acute bronchospasm in severe asthma exacerbations.
* Management of torsades de pointes.
## Adult Dosing
* **Hypomagnesemia:**
* Severe deficiency: 4-6 grams IV infusion over 4-10 hours. Subsequent doses based on serum magnesium levels.
* Less severe deficiency: 1-2 grams IV infusion over 5-60 minutes.
* **Eclampsia prophylaxis/treatment:** 4-6 grams IV loading dose infused over 5-10 minutes, followed by a maintenance infusion of 1-2 grams per hour. Adjustments based on clinical response and serum magnesium levels. Dosing may vary by protocol.
* **Acute bronchospasm (severe asthma):** 1-2 grams IV infused over 15-30 minutes.
* **Torsades de Pointes:** 1-2 grams IV diluted in 10-50 mL D5W or NS and infused over 5-10 minutes. Repeat doses may be given.
## Pediatric Dosing
* **Hypomagnesemia:** Dosing is highly variable and based on severity and protocol. A common regimen for severe deficiency is 25-50 mg/kg IV infused over 4 hours, not to exceed 2 grams. Subsequent doses based on serum magnesium.
* **Eclampsia:** Not typically used in pediatric patients.
* **Acute bronchospasm:** 25-50 mg/kg IV infused over 10-20 minutes, maximum 2 grams.
* **Torsades de Pointes:** 25-50 mg/kg IV infused over 10-20 minutes, maximum 2 grams.
## Dose Adjustments
* **Renal Impairment:** Magnesium is renally excreted. Use with caution in patients with impaired renal function. Reduce dose and monitor serum magnesium levels closely. Avoid in severe renal impairment.
## Contraindications
* Hypermagnesemia.
* Heart block.
* Myocardial infarction.
* Fecal impaction (for rectal administration, which is not parenteral).
* Anuria.
## Adverse Effects
* **Common:** Flushing, warmth, sweating, hypotension, nausea, vomiting, drowsiness, decreased reflexes.
* **Serious:** Respiratory depression, cardiac arrest, hypermagnesemia (leading to neuromuscular blockade, loss of deep tendon reflexes, altered mental status, ECG changes, and asystonia).
## Key Drug Interactions
* **Neuromuscular blockers:** Increased neuromuscular blockade.
* **Calcium channel blockers:** Potential for additive hypotensive effects and bradycardia.
* **Digitalis glycosides:** Can potentiate cardiac toxicity.
* **Nifedipine:** Increased risk of hypotension.
## Monitoring
* **Serum magnesium levels:** Monitor frequently, especially during continuous infusions and in patients with renal impairment. Therapeutic range is typically 1.7-2.2 mmol/L (4-7 mg/dL) for most indications, though higher levels may be targeted for eclampsia.
* **Vital signs:** Blood pressure, heart rate, respiratory rate.
* **Deep tendon reflexes:** Loss of reflexes indicates toxicity.
* **Urine output:** Monitor for adequate renal function.
* **ECG:** Monitor for signs of hypermagnesemia (e.g., PR, QRS, and QT interval prolongation).
## Clinical Pearls
* Magnesium sulfate is highly irritating to veins; dilute appropriately and infuse slowly to minimize phlebitis.
* Always have IV calcium available (e.g., calcium gluconate 1 gram IV) as an antidote for severe magnesium toxicity.
* In eclampsia, continuous infusion is typically guided by clinical response and serum magnesium levels, which should be maintained between 4.2-8.4 mg/dL (1.7-3.5 mmol/L).
* Intravenous magnesium sulfate should be administered with caution in patients receiving other CNS depressants.
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**Disclaimer:** This information is intended for clinical use and is not a substitute for professional medical advice. Always consult the most current prescribing information and relevant institutional protocols before administering any medication.
