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# Magnesium Sulphate
## Overview
Magnesium sulphate is an electrolyte that plays a crucial role in various cellular functions, including nerve impulse transmission and muscle contraction. It is available for intravenous (IV) and intramuscular (IM) administration.
## Primary Indications
* Treatment of hypomagnesemia.
* Management of eclampsia and severe pre-eclampsia.
* Treatment of torsades de pointes.
* Adjunctive therapy in acute bronchospasm (e.g., severe asthma).
## Adult Dosing
* **Hypomagnesemia:**
* Severe deficiency (serum magnesium < 1.3 mg/dL): 4-6 grams IV over 5-60 minutes, followed by 1-2 grams per hour by continuous infusion until serum magnesium is normalized. Maintenance doses vary based on renal function and serum magnesium levels.
* Mild to moderate deficiency (serum magnesium 1.3-1.7 mg/dL): 1-2 grams IV or IM every 4-6 hours for 4 doses.
* **Eclampsia/Severe Pre-eclampsia:**
* Loading dose: 4-6 grams IV, infused over 5-10 minutes.
* Maintenance dose: 1-2 grams per hour IV infusion. Dosing may be adjusted based on clinical response and serum magnesium levels. IM dosing is also an option, typically 5 grams IM in each buttock initially, followed by 5 grams IM every 4 hours.
* **Torsades de Pointes:** 1-2 grams IV, diluted in 10 mL of D5W and administered IV push over 5-10 minutes. May repeat doses every 5 minutes as needed. Continuous infusion of 0.5-1 gram per hour may be used for sustained management.
* **Acute Bronchospasm:** 2 grams IV, diluted in 100 mL of normal saline or D5W, infused over 15-20 minutes.
## Pediatric Dosing
* **Hypomagnesemia:** Dosing varies significantly by age and severity. A common approach for severe hypomagnesemia is 25-50 mg/kg IV (maximum 2 grams) infused over 10-20 minutes, followed by a continuous infusion of 10-30 mg/kg/hour (maximum 1 gram/hour). Precise dosing should follow institutional protocols or expert consultation.
* **Eclampsia/Pre-eclampsia:** Pediatric dosing is not typically established for this indication.
* **Torsades de Pointes:** 25-50 mg/kg IV (maximum 2 grams) as a rapid infusion over 10-20 minutes.
* **Acute Bronchospasm:** 25-40 mg/kg IV (maximum 2 grams) infused over 15-30 minutes.
## Dose Adjustments
Dose reduction is necessary in patients with impaired renal function. Monitor serum magnesium levels closely.
## Contraindications
* Heart block.
* Hypermagnesemia.
* Myocardial damage.
* Shock.
## Adverse Effects
Common: Flushing, sweating, nausea, vomiting, hypotension, muscle weakness, lethargy, hyporeflexia.
Serious: Respiratory depression, cardiac arrhythmias, cardiac arrest, hyperthermia.
## Key Drug Interactions
* **Neuromuscular Blockers:** Magnesium can potentiate the effects of neuromuscular blocking agents, leading to prolonged neuromuscular blockade.
* **Calcium Channel Blockers:** Concurrent use may increase the risk of hypotension and bradycardia.
* **Digitalis Glycosides:** High doses of magnesium can potentiate digitalis toxicity in the presence of hypokalemia or hypocalcemia.
## Monitoring
* **Serum Magnesium Levels:** Essential for dose titration and assessment of efficacy/toxicity. Target levels vary by indication.
* **Renal Function:** Crucial for dose adjustment.
* **Vital Signs:** Blood pressure, heart rate, respiratory rate.
* **Deep Tendon Reflexes:** Loss of reflexes may indicate magnesium toxicity.
* **Urine Output:** Adequate renal excretion is important.
* **ECG:** To monitor for cardiac effects, particularly in torsades de pointes treatment.
## Clinical Pearls
* Always dilute magnesium sulphate before IV administration to reduce the risk of pain, phlebitis, and hypotension.
* Rapid IV infusion can cause hypotension, flushing, and cardiac depression.
* Magnesium toxicity is characterized by loss of deep tendon reflexes, somnolence, ECG changes, respiratory depression, and ultimately cardiac arrest.
* Antidote for magnesium toxicity is IV calcium (e.g., calcium chloride or calcium gluconate).
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**Disclaimer:** This information is intended for clinical professionals. Always consult the most current prescribing information and institutional protocols for complete and up-to-date guidance.
