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# Magnesium Sulphate
## Overview
Magnesium sulphate is an inorganic salt used to treat and prevent hypomagnesemia and as an anticonvulsant in conditions like pre-eclampsia and eclampsia. It also has a role in acute asthma exacerbations and torsades de pointes.
## Primary Indications
* Hypomagnesemia (replacement therapy)
* Prevention and treatment of seizures in pre-eclampsia and eclampsia
* Torsades de Pointes
* Acute severe asthma exacerbations (adjunctive therapy)
## Adult Dosing
Dosing is highly variable based on indication and clinical scenario. Specific doses should follow institutional protocols.
* **Hypomagnesemia:**
* Mild deficiency: 1 gram IV infused over 1 hour, then 1 gram every 4-6 hours as needed.
* Severe deficiency: 4-5 grams IV infused over 3-4 hours, then 1-2 grams per hour as a continuous infusion.
* Intramuscular: 1 gram every 6 hours for 4 doses.
* **Eclampsia/Pre-eclampsia:** Loading dose: 4-6 grams IV over 5-20 minutes. Maintenance infusion: 1-2 grams per hour. Infusion duration typically 24 hours after seizure or last convulsion.
* **Torsades de Pointes:** 1-2 grams IV diluted in 100-1000 mL solution, infused over 5-60 minutes. May repeat. Continuous infusion of 0.5-1 gram per hour may follow.
* **Asthma (adjunctive):** 1-2 grams IV infused over 15-30 minutes.
## Pediatric Dosing
Dosing in pediatrics is less standardized and often based on weight and clinical context. Consult pediatric-specific guidelines or protocols.
* **Hypomagnesemia:** Generally 20-50 mg/kg/dose IV over 1-3 hours. Maximum single dose of 2 grams. May be repeated every 4-12 hours.
* **Eclampsia (rarely used):** May follow adult dosing principles with careful calculation based on weight and renal function.
## Dose Adjustments
* **Renal Impairment:** Magnesium is renally excreted. Reduce dose and/or increase interval in patients with impaired renal function. Monitor magnesium levels closely. Use with extreme caution or avoid in severe renal failure.
## Contraindications
* Hypermagnesemia
* Heart block
* Myocardial infarction (if risk of heart block)
* Heart failure
* Hypotension
* Shock
* Severe renal impairment
## Adverse Effects
Common: Flushing, warmth, hypotension, decreased reflexes, drowsiness, nausea, vomiting.
Serious: Respiratory depression, cardiac arrest, hypermagnesemia (especially with renal impairment).
## Key Drug Interactions
* **Neuromuscular Blockers:** Magnesium can potentiate neuromuscular blockade, leading to prolonged muscle weakness or respiratory depression.
* **Calcium Channel Blockers:** Increased risk of hypotension and bradycardia.
* **Cardiac Glycosides:** May worsen cardiac toxicity in patients receiving digoxin.
* **Tetracyclines/Quinolones:** Magnesium can decrease absorption; administer separately by at least 2 hours.
## Monitoring
* Serum magnesium levels (especially with continuous infusions or renal impairment)
* Respiratory rate
* Deep tendon reflexes
* Blood pressure
* Urine output
* Electrocardiogram (ECG) in high-dose or prolonged therapy
## Clinical Pearls
* Magnesium sulphate is highly irritating to veins; dilute appropriately and infuse slowly to minimize phlebitis and local pain.
* Always have calcium gluconate readily available as an antidote for severe magnesium toxicity.
* Monitor for signs of hypermagnesemia (hypotension, bradycardia, lethargy, decreased reflexes, respiratory depression) which are more likely in renal impairment or with rapid IV administration.
* When used for eclampsia, monitor fetal heart rate for potential bradycardia.
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**Disclaimer:** This information is intended for healthcare professionals. Always consult the most current prescribing information and relevant guidelines for complete details. Practice guidelines and institutional protocols may vary.
