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# Magnesium Sulphate
## Overview
Magnesium sulphate is an essential mineral and electrolyte used to treat and prevent hypomagnesemia and for its tocolytic, anticonvulsant, and antiarrhythmic properties.
## Primary Indications
* Treatment and prevention of hypomagnesemia.
* Prevention of seizures in preeclampsia and eclampsia.
* Management of status epilepticus when other anticonvulsants fail.
* Tocolysis to delay preterm labor.
* Treatment of torsades de pointes.
* Management of severe bronchospasm in asthma refractory to standard treatment.
## Adult Dosing
* **Hypomagnesemia:**
* Intravenous (IV): 1 to 6 grams (as 10% or 50% solution) infused over 5 to 60 minutes, followed by a continuous infusion of 0.5 to 1 gram per hour.
* Intramuscular (IM): 1 gram every 4 hours as needed.
* **Preeclampsia/Eclampsia Prophylaxis:** Loading dose: 4 grams IV infused over 5 to 10 minutes. Maintenance dose: 1 to 2 grams per hour IV infusion.
* **Torsades de Pointes:** 1 to 2 grams IV in 50-100 mL of D5W over 5 to 10 minutes. May repeat q 5-15 minutes. Further doses can be given as continuous infusion.
* **Status Epilepticus/Asthma:** Dosing often guided by protocol, typically 1-2 grams IV over 5-15 minutes, potentially repeated.
## Pediatric Dosing
* **Hypomagnesemia:**
* IV: 25-50 mg/kg per dose (maximum 2 grams) infused over 10 minutes. May repeat q 4-12 hours.
* IM: 25-50 mg/kg per dose (maximum 2 grams).
* **Preeclampsia/Eclampsia Prophylaxis:** Dosing is less established and often based on adult protocols extrapolated to weight. Consult pediatric guidelines or local protocol.
* **Status Epilepticus/Asthma:** Typically 25-50 mg/kg IV over 10-20 minutes, maximum 2 grams. Consult specific pediatric emergency guidelines.
## Dose Adjustments
* **Renal Impairment:** Use with caution. Magnesium is renally excreted; accumulation can occur. Reduce dose and monitor serum magnesium levels closely. In severe renal impairment, dose may need significant reduction or discontinuation.
## Contraindications
* Myocardial damage.
* Heart block.
* Hypermagnesemia.
* Hyperkalemia (with caution, can worsen).
* Shock.
* Anuria.
## Adverse Effects
Common: Flushing, sweating, hypotension, nausea, vomiting, drowsiness, decreased deep tendon reflexes.
Serious: Respiratory depression, cardiac arrhythmias, cardiac arrest, coma, hypermagnesemia (weakness, lethargy, hyporeflexia, ECG changes, hypotension, respiratory arrest, cardiac arrest).
## Key Drug Interactions
* **Neuromuscular Blockers:** Magnesium can potentiate neuromuscular blockade, leading to prolonged respiratory depression.
* **Calcium Channel Blockers:** Additive hypotensive effects and increased risk of cardiac conduction abnormalities.
* **Other CNS Depressants:** Additive CNS depression.
* **Tetracyclines and Quinolones:** Magnesium can decrease absorption of these antibiotics; administer at least 2 hours before or 4-6 hours after magnesium.
## Monitoring
* Serum magnesium levels (especially with IV infusions, renal impairment, or prolonged use).
* Respiratory rate and depth.
* Blood pressure.
* Deep tendon reflexes.
* Urine output.
* ECG, particularly with IV administration or risk of hypermagnesemia.
## Clinical Pearls
* Always dilute magnesium sulphate for IV infusion to avoid rapid administration which can cause hypotension and cardiac arrest.
* Monitor for signs of magnesium toxicity, especially in patients with renal insufficiency.
* Magnesium sulphate is incompatible with many IV solutions; check compatibility before co-administration.
* For IM administration, no more than 2 mL (or 0.2g) of a 50% solution should be injected into a single site due to pain and risk of tissue damage.
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**Disclaimer:** This information is for educational purposes only and does not substitute for professional medical advice. Always consult the most current prescribing information and institutional protocols before administering any medication.
