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# Magnesium Sulphate
## Overview
Magnesium sulphate is an essential mineral that plays a vital role in numerous biochemical functions. It is available in intravenous (IV) and intramuscular (IM) formulations.
## Primary Indications
* Hypomagnesemia (treatment and prevention)
* Eclampsia and pre-eclampsia (treatment of seizures)
* Torsades de Pointes
* Bronchospasm (adjunctive therapy in severe cases)
## Adult Dosing
* **Hypomagnesemia:**
* *Severe depletion:* 4-5 g IV infusion over 5-60 minutes, followed by 1-2 g/hour infusion as needed.
* *Less severe depletion:* 1 g IV or IM every 6 hours for 4 doses.
* **Eclampsia/Pre-eclampsia:** Loading dose: 4-6 g IV infusion over 5-20 minutes. Maintenance infusion: 1-2 g/hour. Alternative IM dosing: 5 g IM in each buttock initially, followed by 5 g IM every 4 hours. Dosing may vary by protocol.
* **Torsades de Pointes:** 1-2 g IV in 10-20 mL D5W or NS over 5-10 minutes. May repeat bolus or start infusion of 2 g/hour.
* **Bronchospasm:** 1-2 g IV infusion over 15-30 minutes.
## Pediatric Dosing
* **Hypomagnesemia:** Dosing varies significantly based on age and severity. Commonly, 25-50 mg/kg/dose IV or IM every 4-6 hours. Maximum single dose typically 2 g. Consult specific pediatric guidelines.
* **Eclampsia/Pre-eclampsia:** Similar to adult regimens, but often weight-based. Refer to institutional protocols.
* **Torsades de Pointes:** 25-50 mg/kg IV bolus over 10-20 minutes. Infusion of 2-5 mg/kg/minute may follow.
## Dose Adjustments
Renal impairment: Use with caution. Magnesium is renally eliminated. Reduce dose and monitor serum magnesium levels closely. Avoid in severe renal failure if possible.
## Contraindications
* Hypermagnesemia
* Heart block
* Myocardial infarction (relative contraindication)
* Hyperpotassemia (relative contraindication)
* Severe renal dysfunction
## Adverse Effects
* Flushing, hypotension, somnolence, decreased reflexes, respiratory depression, cardiac arrest.
* Hypermagnesemia: nausea, vomiting, ileus, urinary retention, hypotension, bradycardia, ECG changes, CNS depression, muscle weakness, respiratory paralysis.
## Key Drug Interactions
* **Neuromuscular Blockers:** Potentiates neuromuscular blockade.
* **Calcium Salts:** May antagonize cardiac and CNS effects of magnesium.
* **Nifedipine:** Increased risk of hypotension and neuromuscular blockade.
* **Tetracyclines and Bisphosphonates:** Magnesium may decrease absorption; separate administration by at least 2 hours.
## Monitoring
* **Serum magnesium levels:** Monitor closely, especially during infusions and in patients with renal impairment. Target levels vary by indication (e.g., 4-7 mEq/L for eclampsia).
* **Renal function (BUN, creatinine).**
* **Deep tendon reflexes:** Loss of reflexes indicates toxicity.
* **Respiratory rate and depth.**
* **Cardiac rhythm and blood pressure.**
* **Urine output.**
## Clinical Pearls
* Magnesium sulphate is a CNS depressant and vasodilator.
* Always have calcium gluconate available as an antidote for magnesium toxicity.
* IV administration is preferred for rapid correction and in emergencies. IM administration can be painful.
* Dilute IV magnesium sulphate for infusion to prevent local irritation and phlebitis.
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*Disclaimer: This information is intended for clinical decision support and does not replace comprehensive drug information resources. Always verify current prescribing information with the manufacturer's package insert or other authoritative sources.*
