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# Magnesium Sulphate
## Overview
Magnesium sulphate is an electrolyte that plays a crucial role in numerous biochemical reactions in the body. It is available for intravenous (IV) and intramuscular (IM) administration.
## Primary Indications
* Treatment of hypomagnesemia.
* Management of severe preeclampsia and eclampsia.
* Treatment of torsades de pointes.
* Adjunctive therapy in acute asthma exacerbations.
## Adult Dosing
* **Hypomagnesemia:**
* **IV infusion:** 4 grams as a loading dose, followed by 1-2 grams per hour. Dosing may be adjusted based on serum magnesium levels and clinical response. Maximum infusion rate generally 2 grams/hour.
* **IM injection:** 1 gram every 4 hours as needed.
* **Preeclampsia/Eclampsia:**
* **IV infusion (eclampsia):** 4 grams as a loading dose over 5 minutes, followed by 1-2 grams per hour maintenance infusion. (Specific protocols may vary, e.g., Zinsargen protocol).
* **Torsades de Pointes:**
* **IV infusion:** 1-2 grams diluted in 10-50 mL dextrose 5% or normal saline, administered over 5-10 minutes. Repeat doses may be given as continuous infusion.
* **Acute Asthma Exacerbations:**
* **IV infusion:** 1.2 to 2 grams diluted in 100 mL normal saline, administered over 15-20 minutes.
## Pediatric Dosing
* **Hypomagnesemia:** Dosing is highly variable and based on serum magnesium levels. A common starting point for severe hypomagnesemia is 25-50 mg/kg (elemental magnesium) IV over 4-6 hours. Subsequent doses should be guided by serum magnesium concentrations.
* **Eclampsia:** Dosing follows adult protocols or specific pediatric emergency guidelines.
* **Asthma Exacerbations:** 25-50 mg/kg IV over 15-30 minutes. Maximum dose typically 2 grams.
## Dose Adjustments
Dose adjustments are primarily based on serum magnesium levels and renal function. In patients with impaired renal function, reduce the maintenance dose.
## Contraindications
* Hypermagnesemia.
* Heart block.
* Myocardial infarction (caution).
* Gastrointestinal obstruction.
* Rectal bleeding (for rectal administration, if applicable).
## Adverse Effects
Common: Flushing, hypotension, nausea, vomiting, diaphoresis, drowsiness, decreased deep tendon reflexes.
Serious: Respiratory depression, cardiac arrest, hypermagnesemia, loss of deep tendon reflexes, decreased urine output.
## Key Drug Interactions
* **Calcium:** Can antagonize the effects of magnesium; concurrent administration may lead to arrhythmias.
* **Neuromuscular Blocking Agents:** Magnesium can potentiate neuromuscular blockade; caution and careful monitoring are required.
* **Nifedipine:** Increased risk of hypotension and neuromuscular blockade.
* **Tetracyclines and Quinolones:** Magnesium can decrease absorption; separate administration by at least 2 hours.
## Monitoring
* Serum magnesium levels (essential for dosing adjustments).
* Deep tendon reflexes.
* Respiratory rate and function.
* Blood pressure.
* Urine output.
* Electrocardiogram (ECG), especially in patients receiving high doses or with cardiac risk factors.
## Clinical Pearls
* Magnesium sulphate should be administered slowly to avoid adverse effects like hypotension and flushing.
* Monitor for signs of hypermagnesemia (e.g., absent reflexes, hypotension, respiratory depression), especially in patients with renal impairment.
* For torsades de pointes, magnesium is effective regardless of baseline magnesium levels.
* Ensure adequate hydration and renal function before administering magnesium sulphate.
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**Disclaimer:** This information is intended for healthcare professionals and is not a substitute for professional medical advice. Always consult the most current prescribing information and local institutional protocols for definitive guidance.
