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# Magnesium Sulphate
## Overview
Magnesium sulfate is an electrolyte supplement used for magnesium replacement and as an anticonvulsant. It is available in intravenous (IV) and intramuscular (IM) formulations.
## Primary Indications
* **Hypomagnesemia:** Treatment of magnesium deficiency.
* **Eclampsia/Preeclampsia:** Prevention and treatment of seizures in patients with eclampsia and preeclampsia.
* **Torsades de Pointes:** Management of polymorphic ventricular tachycardia associated with prolonged QT interval.
* **Status Asthmaticus:** Adjunctive treatment in severe asthma exacerbations.
## Adult Dosing
* **Hypomagnesemia (Severe):**
* **IV:** 4-6 g (32-48 mEq) infused over 10-60 minutes, followed by a maintenance infusion of 1-2 g (8-16 mEq) per hour, or 1 g (8 mEq) IM every 4 hours as needed.
* **IM:** 1 g (8 mEq) every 4 hours for 4 doses.
* **Eclampsia Prophylaxis/Treatment:**
* **Loading Dose (IV):** 4-6 g (32-48 mEq) infused over 5-10 minutes.
* **Maintenance Dose (IV):** 1-2 g (8-16 mEq) per hour. May be adjusted based on clinical response and magnesium levels.
* **IM:** 5 g (40 mEq) in each buttock (total 10 g) for loading, followed by 5 g (40 mEq) in alternating buttocks every 4 hours.
* **Torsades de Pointes:**
* **IV:** 1-2 g (8-16 mEq) diluted in 10 mL D5W, infused over 5-10 minutes. Repeat doses may be given. Further infusions of 0.5-1 g/hour may be required.
* **Status Asthmaticus:**
* **IV:** 2 g (16 mEq) diluted in 100 mL NS, infused over 20 minutes.
## Pediatric Dosing
Dosing in pediatrics is highly variable and often based on local protocols and magnesium levels.
* **Hypomagnesemia:**
* **IV:** 25-50 mg/kg/dose (0.1-0.2 mEq/kg/dose) over 10-60 minutes, not to exceed 1 g/dose. Maintenance infusions may be given.
* **Eclampsia:** Generally not recommended due to lack of established pediatric guidelines.
## Dose Adjustments
* **Renal Impairment:** Magnesium is renally excreted. Reduce dose and monitor serum magnesium levels closely in patients with impaired renal function. Avoid if CrCl < 30 mL/min.
## Contraindications
* Hypermagnesemia.
* Heart block.
* Myocardial infarction.
* Digitalis toxicity.
* Severe renal impairment (CrCl < 30 mL/min).
## Adverse Effects
Common: Flushing, sweating, hypotension, somnolence, nausea, vomiting, decreased deep tendon reflexes.
Serious: Respiratory depression, cardiac arrhythmias, cardiac arrest, paralysis, hypermagnesemia (loss of deep tendon reflexes, hypotension, ECG changes, cardiac arrest).
## Key Drug Interactions
* **Neuromuscular Blockers (e.g., succinylcholine, vecuronium):** Magnesium can potentiate neuromuscular blockade, increasing the risk of prolonged respiratory depression.
* **Calcium Channel Blockers:** Additive hypotensive effects and potential for bradycardia.
* **Tetracyclines, Bisphosphonates, Quinolones:** Magnesium can decrease the absorption of these oral drugs; administer at least 2 hours apart.
## Monitoring
* **Serum Magnesium Levels:** Essential, especially with IV infusions and in renal impairment. Target levels vary by indication (e.g., 4-7 mEq/L for eclampsia).
* **Renal Function:** Monitor BUN and creatinine.
* **Vital Signs:** Blood pressure, heart rate, respiratory rate.
* **Deep Tendon Reflexes:** Assess for loss of reflexes, an early sign of hypermagnesemia.
* **Urine Output:** Ensure adequate renal function.
* **ECG:** Monitor for changes, especially in patients with cardiac conditions or receiving high doses.
## Clinical Pearls
* Magnesium sulfate is a potent medication; use with caution and careful monitoring.
* Rapid IV infusion can cause hypotension and cardiovascular depression. Dilute and infuse slowly as recommended.
* The IM route can be painful.
* Always verify the concentration and intended use (e.g., 50% solution) before administration.
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*This information is intended for clinical use and does not substitute for professional medical advice. Always consult the most current prescribing information and institutional protocols.*
