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# Magnesium Sulphate
## Overview
Magnesium sulphate is an electrolyte that plays a crucial role in numerous physiological processes, including neuromuscular transmission, cardiac conduction, and enzyme function. It is available in intravenous and intramuscular formulations.
## Primary Indications
* Treatment of hypomagnesemia.
* Management of eclampsia and preeclampsia.
* Treatment of severe asthma exacerbations (off-label use).
* Management of torsades de pointes.
* Prevention and treatment of cardiac arrhythmias associated with hypomagnesemia.
## Adult Dosing
Dosing varies significantly based on indication and severity.
* **Hypomagnesemia:**
* **Mild to Moderate:** 1-4 grams (8-32 mEq) intravenously (IV) or intramuscularly (IM) over 1-4 hours, followed by 1-2 grams (8-16 mEq) every 4-6 hours as needed.
* **Severe (with cardiac arrhythmias/seizures):** 4-5 grams (32-40 mEq) IV over 5-60 minutes. Maintenance infusion of 1-2 grams (8-16 mEq) per hour may be required.
* **Eclampsia/Preeclampsia:** Load: 4-6 grams (32-48 mEq) IV over 5-20 minutes. Maintenance: 1-2 grams (8-16 mEq) per hour via continuous infusion. Dosing may be adjusted per local protocol.
* **Torsades de Pointes:** 1-2 grams (8-16 mEq) IV, often as a bolus followed by an infusion.
* **Severe Asthma:** 1-2 grams (8-16 mEq) IV over 15-20 minutes.
## Pediatric Dosing
Dosing is less standardized and often guided by institutional protocols.
* **Hypomagnesemia:** Typical initial dose is 25-50 mg/kg/dose (0.2-0.4 mEq/kg/dose) IV or IM, not to exceed 2 grams per dose. Doses may be repeated every 4-12 hours.
* **Eclampsia:** Not typically used in pediatric patients.
* **Severe Asthma:** 25-75 mg/kg/dose (0.2-0.6 mEq/kg/dose) IV over 15-30 minutes. Maximum dose usually 2 grams.
## Dose Adjustments
* **Renal Impairment:** Use with caution. Magnesium is renally excreted. In severe renal impairment, doses should be reduced, and serum magnesium levels monitored closely.
## Contraindications
* Hypermagnesemia.
* Heart block greater than first-degree (unless patient has a pacemaker).
* Myocardial infarction.
* Bowel obstruction or perforation.
* Hypermagnesemia.
## Adverse Effects
* **Common:** Flushing, warmth, diaphoresis, hypotension, nausea, vomiting.
* **Serious:** Respiratory depression, cardiac arrest, absent deep tendon reflexes, muscle weakness, confusion, coma.
## Key Drug Interactions
* **Nifedipine/Calcium Channel Blockers:** Increased risk of hypotension and neuromuscular blockade.
* **Neuromuscular Blocking Agents:** Potentiated neuromuscular blockade.
* **Tetracyclines/Quinolones:** Reduced absorption due to complex formation. Administer these drugs at least 2-3 hours before or 4-6 hours after magnesium sulphate.
* **Digoxin:** Increased risk of digoxin toxicity with IV magnesium.
## Monitoring
* **Serum Magnesium Levels:** Essential, especially with prolonged or high-dose therapy, renal impairment, or suspicion of toxicity. 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 toxicity.
* **Urine Output:** Important indicator of renal function and fluid status.
* **ECG:** If cardiac arrhythmias are present or suspected.
## Clinical Pearls
* Administer IV magnesium sulphate slowly to avoid hypotension and flushing.
* Have calcium gluconate readily available as an antidote for magnesium toxicity.
* For IV administration, dilute magnesium sulphate in a compatible intravenous solution (e.g., D5W, NS).
* Intramuscular administration can be painful; consider lidocaine with IM injections.
* Monitor for signs of hypermagnesemia, particularly in patients with impaired renal function.
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**Disclaimer:** This information is intended for healthcare professionals. Always consult the most current prescribing information, institutional protocols, and your formulary before administering any medication.
