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# Magnesium Sulphate
## Overview
Magnesium sulphate is an essential mineral that plays a vital role in numerous physiological processes, including neuromuscular function, cardiac rhythm, and enzyme activity.
## Primary Indications
* Treatment of hypomagnesemia
* Prevention and treatment of seizures in pre-eclampsia and eclampsia
* Management of torsades de pointes
* Bronchodilation in severe asthma exacerbations (off-label use, typically in critical care settings)
## Adult Dosing
* **Hypomagnesemia:**
* **Severe (serum Mg < 1.3 mg/dL):** 4-5 g (32-40 mEq) IV infusion over 10-20 minutes, followed by 1-2 g/hr (8-16 mEq/hr) infusion for up to 24 hours or until serum Mg is corrected. Alternatively, 1 g IV every 10-15 minutes for up to 5 doses.
* **Mild/Moderate:** 1-2 g (8-16 mEq) IV infusion over 1-2 hours, or 1 g IM every 6 hours for 4 doses.
* **Oral repletion:** 3-6 g/day divided into doses.
* **Eclampsia/Pre-eclampsia:** 4-6 g (32-48 mEq) IV loading dose over 5-20 minutes, followed by a maintenance infusion of 1-2 g/hr (8-16 mEq/hr). An alternative intramuscular regimen is 5 g IM in each buttock initially, followed by 5 g IM every 4 hours. Dosing should be guided by local protocol and clinical response.
* **Torsades de Pointes:** 1-2 g (8-16 mEq) IV bolus, followed by 1 g/hr (8 mEq/hr) IV infusion.
* **Asthma (off-label):** 1-2 g (8-16 mEq) IV infusion over 15-20 minutes.
## Pediatric Dosing
Dosing varies significantly based on indication and severity. Generally based on weight and serum magnesium levels.
* **Hypomagnesemia:** IV doses range from 25-50 mg/kg (0.2-0.4 mEq/kg) per dose, infused over 5-10 minutes, not to exceed 2 g (16 mEq) per dose. Maintenance infusions are typically 20-30 mg/kg/day (0.16-0.24 mEq/kg/day).
* **Eclampsia/Pre-eclampsia:** Dosing protocols exist but are complex and require careful monitoring; generally follow adult principles adapted for weight.
* **Torsades de Pointes:** 25-50 mg/kg (0.2-0.4 mEq/kg) IV over 10-20 minutes.
## Dose Adjustments
* **Renal Impairment:** Reduce dose and monitor magnesium levels closely. In severe renal impairment, administration may be contraindicated.
## Contraindications
* Hypermagnesemia
* Heart block
* Myocardial infarction
* Gastrointestinal obstruction (for oral administration)
## Adverse Effects
* **Common:** Flushing, warmth, hypotension, somnolence, hyporeflexia, nausea, vomiting.
* **Serious:** Respiratory depression, cardiac arrhythmias, cardiac arrest, hypermagnesemia (especially with renal impairment).
## Key Drug Interactions
* **Nifedipine, Calcium Channel Blockers:** Increased risk of hypotension.
* **Neuromuscular Blockers (e.g., succinylcholine, vecuronium):** Potentiates neuromuscular blockade.
* **Tetracyclines, Bisphosphonates:** Decreased absorption when administered concurrently (separate administration by at least 2-3 hours).
## Monitoring
* **Essential:** Serum magnesium levels, blood pressure, respiratory rate, deep tendon reflexes, urine output.
* **Consider:** ECG, serum calcium and potassium levels.
## Clinical Pearls
* Magnesium sulphate is administered via IV, IM, or PO routes. IV infusion is preferred for rapid correction of severe hypomagnesemia and for eclampsia.
* IM injections can be painful; consider co-administration with lidocaine (1% without epinephrine).
* Monitor for signs of magnesium toxicity, which can be severe and life-threatening.
* Ensure adequate IV access and resuscitation equipment are available when administering IV magnesium.
* Dosing for eclampsia/pre-eclampsia can vary by institution; adherence to established protocols is critical.
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*Please verify current prescribing information for the most up-to-date details.*
