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# Magnesium Sulfate
## Overview
Magnesium sulfate is an electrolyte that is essential for the function of many enzyme systems, neuromuscular transmission, and myocardial contractility. It is available in oral and parenteral formulations.
## Primary Indications
* Treatment of hypomagnesemia
* Prevention and treatment of seizures in preeclampsia/eclampsia
* Management of torsades de pointes
* Bronchodilation in severe asthma exacerbations (adjunctive therapy)
## Adult Dosing
* **Hypomagnesemia:**
* **Severe (serum magnesium < 1 mg/dL):** 4-5 g (32-40 mEq) IV infusion over 5-10 minutes, followed by 1-2 g (8-16 mEq) per hour until serum magnesium is corrected. Alternatively, 1 g (8 mEq) IM every 6 hours for 4 doses.
* **Mild-to-moderate (serum magnesium 1-1.5 mg/dL):** 1-2 g (8-16 mEq) IM or IV infusion over 3-6 hours. Oral magnesium can be used for less severe cases, typically 20-40 mEq/day divided into 4 doses.
* **Preeclampsia/Eclampsia:** Loading dose: 4-6 g (32-48 mEq) IV infusion over 5-20 minutes. Maintenance dose: 1-2 g (8-16 mEq) per hour IV infusion. Alternatively, 5 g (40 mEq) IM in each buttock initially, followed by 5 g (40 mEq) IM every 4 hours.
* **Torsades de Pointes:** 1-2 g (8-16 mEq) IV in 10 mL of D5W rapidly over 5-20 minutes. May repeat dose and/or follow with an infusion of 0.5-1 g (4-8 mEq) per hour.
* **Asthma Exacerbation:** 1-2 g (8-16 mEq) IV infusion over 15-30 minutes.
## Pediatric Dosing
* **Hypomagnesemia:** Dosing varies significantly based on age, weight, and severity. Consult specific pediatric guidelines or local protocols. A common regimen for severe hypomagnesemia is 25-50 mg/kg (0.2-0.4 mEq/kg) IV infusion over 5-10 minutes, not to exceed 2 g (16 mEq).
* **Preeclampsia/Eclampsia:** Not typically used in pediatric patients.
* **Torsades de Pointes:** 25-50 mg/kg (0.2-0.4 mEq/kg) IV infusion over 10-20 minutes, not to exceed 2 g (16 mEq). May repeat and follow with infusion.
* **Asthma Exacerbation:** 25-50 mg/kg (0.2-0.4 mEq/kg) IV infusion over 15-30 minutes, maximum 2 g (16 mEq).
## Dose Adjustments
* **Renal Impairment:** Magnesium is renally excreted. Use with caution in patients with renal impairment. Reduce dose and monitor serum magnesium levels closely. In severe renal impairment, parenteral magnesium should generally be avoided.
## Contraindications
* Hypermagnesemia
* Heart block (greater than first degree) or myocardial damage (in patients receiving IV magnesium)
## Adverse Effects
* **Common:** Flushing, warmth, hypotension, nausea, vomiting, somnolence, decreased deep tendon reflexes.
* **Serious:** Respiratory depression, cardiac arrest, hypermagnesemia (especially in renal impairment), loss of deep tendon reflexes, altered mental status, paralysis.
## Key Drug Interactions
* **Neuromuscular Blockers:** Magnesium can potentiate neuromuscular blockade, leading to prolonged respiratory depression.
* **Calcium:** IV calcium may antagonize the cardiac effects of magnesium.
* **Tetracyclines and Fluoroquinolones:** Oral magnesium can decrease the absorption of these antibiotics. Separate administration by at least 2 hours.
## Monitoring
* **Primary:** Serum magnesium levels (especially with prolonged parenteral administration or in renal impairment), respiratory rate, blood pressure, deep tendon reflexes, urine output.
* **Secondary:** ECG (if indicated for cardiac effects).
## Clinical Pearls
* Parenteral magnesium sulfate can cause pain and phlebitis at the injection site; slow infusion rates and dilution may help.
* Observe patients for signs of magnesium toxicity, particularly decreased deep tendon reflexes, somnolence, and respiratory depression.
* Magnesium sulfate is a Category D drug for routine use in pregnancy, but it is a cornerstone of treatment for preeclampsia/eclampsia.
* In the setting of torsades de pointes, magnesium is considered first-line therapy regardless of serum magnesium level.
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**Disclaimer:** This information is intended for healthcare professionals and does not replace the need to consult current prescribing information, clinical guidelines, and institutional protocols. Always verify drug information with authoritative sources before making clinical decisions.
