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# Magnesium Sulfate
## Overview
Magnesium sulfate is an electrolyte that is essential for the normal functioning of the neuromuscular system and acts as a cofactor in many enzymatic reactions.
## Primary Indications
* Treatment of hypomagnesemia.
* Prevention and treatment of eclampsia and preeclampsia.
* Management of torsades de pointes.
* Treatment of severe asthma exacerbations (adjunctive therapy).
* Management of acute myocardial infarction (adjunctive therapy).
## Adult Dosing
* **Hypomagnesemia:**
* **Mild deficiency:** 1 gram (8 mEq) intramuscularly (IM) or intravenously (IV) every 6 hours for 4 doses, or 5 grams (40 mEq) added to 1 L of IV fluid infused over 3-4 hours.
* **Severe deficiency:** 4 grams (32 mEq) IV initially, followed by a continuous infusion of 1-2 grams (8-16 mEq) per hour, adjusted based on serum magnesium levels. Maximum infusion rate typically 2 grams/hour.
* **Preeclampsia/Eclampsia:** Loading dose of 4-6 grams IV infused over 5-20 minutes, followed by a maintenance infusion of 1-2 grams per hour. Dosing may vary based on local protocol and patient response.
* **Torsades de Pointes:** 1-2 grams (8-16 mEq) IV in 10-20 mL D5W over 5-10 minutes. Repeat doses may be given every 5-15 minutes. Can also be given as a continuous infusion of 0.5-1 gram per hour.
* **Severe Asthma:** 1.2-2 grams (10-16 mEq) IV infused over 15-20 minutes.
* **Acute Myocardial Infarction:** 8 mmol (approx. 1 gram) IV infusion over 5 minutes, followed by a 16 mmol (approx. 2 grams) infusion over 60 minutes.
## Pediatric Dosing
* **Hypomagnesemia:** Dosing is highly variable and based on serum magnesium levels and clinical status. Typically, 25-50 mg/kg/dose IV every 6-8 hours. Maintenance infusions can range from 100-200 mg/kg/day (max 1000 mg/day or 16 mEq/day) divided and infused over 4-12 hours.
* **Eclampsia:** Loading dose 40 mg/kg (max 2 grams) IV over 5-20 minutes. Maintenance infusion 10 mg/kg/hour (max 6 grams/day or 10 mEq/hour).
* **Torsades de Pointes:** 25-50 mg/kg IV as a single dose, max 2 grams.
## Dose Adjustments
Dose adjustments are primarily guided by serum magnesium levels, renal function, and clinical response. In patients with renal impairment, magnesium should be used with extreme caution and doses reduced.
## Contraindications
* Hypermagnesemia.
* Heart block (greater than first degree) or myocardial damage (in patients receiving IV magnesium).
* Hyperkalemia (use with caution, as magnesium can increase potassium levels).
## Adverse Effects
Common: Flushing, sweating, hypotension, nausea, vomiting, decreased reflexes, drowsiness.
Serious: Respiratory depression, cardiac arrhythmias, cardiac arrest, coma, hypermagnesemia (muscle weakness, bradycardia, hypotension, cardiac arrest).
## Key Drug Interactions
* **Neuromuscular Blockers:** Magnesium can potentiate neuromuscular blockade, leading to prolonged respiratory depression.
* **Calcium Channel Blockers:** Additive hypotensive effects and increased risk of bradycardia and arrhythmias.
* **Antibiotics (e.g., tetracyclines, quinolones):** Magnesium can impair absorption; separate administration by at least 2-3 hours.
* **Bisphosphonates:** Magnesium can decrease absorption; separate administration by at least 2 hours.
## Monitoring
* Serum magnesium levels (prior to and regularly during therapy, especially with IV infusions).
* Renal function (BUN, creatinine).
* Deep tendon reflexes.
* Respiratory rate and depth.
* Blood pressure.
* Urine output.
* ECG (especially with rapid IV administration or in patients with cardiac risk factors).
## Clinical Pearls
* IV magnesium should be administered slowly and with continuous monitoring. Rapid infusion can cause hypotension and other adverse effects.
* When treating hypomagnesemia, it's important to also assess and replete potassium and calcium, as these electrolytes can be depleted with magnesium deficiency.
* IM injections of magnesium sulfate are painful and should be administered deep into a large muscle mass, often with lidocaine.
* In patients with renal insufficiency, magnesium accumulation can lead to toxicity.
This information is intended for clinical decision-making and does not replace a thorough review of current prescribing information and patient-specific factors. Always verify current drug information with official sources before prescribing or administering.
