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# Magnesium Sulphate
## Overview
Magnesium sulphate is an essential mineral that plays a vital role in numerous physiological processes. It is available in intravenous (IV) and intramuscular (IM) formulations for parenteral administration.
## Primary Indications
* Treatment of hypomagnesemia.
* Management of eclampsia and pre-eclampsia.
* Treatment of torsades de pointes.
* Management of severe bronchospasm in asthma refractory to standard therapy.
## Adult Dosing
* **Hypomagnesemia:**
* **Severe deficiency (serum magnesium < 1.7 mg/dL):** 4-5 grams IV infused over 15-60 minutes, followed by 1-2 grams every 4-12 hours as needed, based on serum magnesium levels. Maximum daily dose generally 20-30 grams.
* **Less severe deficiency:** 1-2 grams IV or IM every 6-12 hours for 3-4 doses.
* **Eclampsia/Pre-eclampsia (prophylaxis and treatment):** Loading dose: 4-6 grams IV infused over 5-20 minutes. Maintenance infusion: 1-2 grams per hour. Some protocols utilize IM administration (e.g., 5 grams IM in each buttock initially, followed by 5 grams IM every 4 hours). Dosing protocols can vary significantly; consult local guidelines.
* **Torsades de Pointes:** 1-2 grams IV in 50-100 mL D5W infused over 5-10 minutes. May repeat bolus, followed by an infusion of 0.5-1 gram per hour.
* **Asthma (severe, refractory):** 1.2-2 grams IV infused over 15-20 minutes.
## Pediatric Dosing
Dosing is highly variable and depends on indication and severity. Consult pediatric-specific guidelines.
* **Hypomagnesemia:** Generally 25-50 mg/kg/dose IV over 10-15 minutes. Maximum single dose typically 2 grams. Maintenance doses may be given over several hours.
* **Eclampsia/Pre-eclampsia:** Follows adult protocols, adjusted for weight. Often 40 mg/kg IV loading dose, followed by 10-20 mg/kg/hour infusion.
* **Asthma:** Typically 25-40 mg/kg IV over 15-30 minutes. Maximum single dose typically 2 grams.
## Dose Adjustments
Reduce dose and/or frequency in patients with **renal impairment**. Magnesium is renally excreted. Monitor magnesium levels closely.
## Contraindications
* Myocardial damage.
* Heart block.
* Hypermagnesemia.
* Severe renal dysfunction.
## Adverse Effects
* **Common:** Flushing, sweating, hypotension, nausea, vomiting, decreased deep tendon reflexes.
* **Serious:** Respiratory depression, cardiac arrest, coma, hypermagnesemia (muscle weakness, ECG changes, bradycardia, hypotension).
## Key Drug Interactions
* **Neuromuscular blocking agents:** May potentiate neuromuscular blockade, leading to prolonged respiratory depression.
* **Calcium channel blockers:** Increased risk of hypotension and bradycardia.
* **Digitalis glycosides:** IV magnesium can potentiate digitalis toxicity.
* **Tetracyclines and bisphosphonates:** Oral magnesium can reduce the absorption of these drugs; administer separately.
## Monitoring
* **Serum magnesium levels:** Crucial for guiding therapy and preventing toxicity. Frequency depends on clinical status and dose.
* **Renal function:** Assess baseline and monitor during therapy.
* **Vital signs:** Blood pressure, heart rate, respiratory rate.
* **Deep tendon reflexes:** Assess for signs of magnesium toxicity.
* **Urine output:** Indicator of renal perfusion and function.
* **ECG:** Especially in patients receiving high doses or with cardiac concerns.
## Clinical Pearls
* Magnesium sulphate is a central nervous system depressant.
* IV administration is generally preferred for rapid correction of hypomagnesemia and in emergent situations like eclampsia or torsades de pointes.
* IM injections can be painful; consider administration with lidocaine if tolerated and protocol allows.
* Always use an infusion pump for IV magnesium infusions to ensure controlled administration rate.
* Be aware of the potential for delayed toxicity, especially in renal impairment.
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*This information is intended for educational purposes and is not a substitute for professional medical advice. Always consult the most current prescribing information and institutional protocols before administering any medication.*
