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# Magnesium Sulphate
## Overview
Magnesium sulphate is an electrolyte that plays a crucial role in numerous enzymatic reactions and physiological processes, including neuromuscular transmission and cardiac excitability.
## Primary Indications
* Treatment of hypomagnesemia
* Prevention and treatment of seizures in preeclampsia and eclampsia
* Management of acute severe asthma exacerbations (off-label in some regions)
* Torsades de Pointes
## Adult Dosing
* **Hypomagnesemia:**
* Severe symptomatic hypomagnesemia: 4-5 grams (32-40 mEq) IV infusion over 5-20 minutes. Follow with 1-2 grams (8-16 mEq) per hour by continuous infusion until symptoms resolve and serum magnesium levels normalize.
* Asymptomatic hypomagnesemia: 1 gram (8 mEq) IV infusion over 5-10 minutes every 6 hours for 4 doses. Or 5 grams (40 mEq) IM divided into two doses every 12 hours for 4 doses.
* **Preeclampsia/Eclampsia:** Loading dose: 4-6 grams (32-48 mEq) IV infusion over 15-30 minutes. Maintenance dose: 1-2 grams (8-16 mEq) per hour by continuous IV infusion. Dosing may vary based on local protocol.
* **Torsades de Pointes:** 1-2 grams (8-16 mEq) IV in 10 mL of D5W over 5-10 minutes. Repeat doses as needed. Continuous infusion of 0.5-1 gram (4-8 mEq) per hour may be considered.
* **Acute Asthma (off-label):** 1-2 grams (8-16 mEq) IV infusion over 15-30 minutes.
## Pediatric Dosing
* **Hypomagnesemia:** 25-50 mg/kg/dose IV over 10-20 minutes. Maximum dose 2 grams (16 mEq). May repeat every 4-6 hours as needed. For continuous infusion, 20-30 mg/kg/hour. Dosing may vary based on local protocol.
* **Preeclampsia/Eclampsia:** Dosing is not well established in pediatric patients and should be guided by expert consultation and local protocol.
* **Torsades de Pointes:** 25-50 mg/kg IV over 10-20 minutes. Maximum dose 2 grams (16 mEq). May repeat. Continuous infusion of 10-20 mg/kg/hour may be considered.
## Dose Adjustments
* **Renal Impairment:** Use with caution. Reduce dose and monitor serum magnesium levels closely. Magnesium is renally excreted.
## Contraindications
* Hypermagnesemia
* Heart block
* Myocardial infarction
* Severe renal impairment
## Adverse Effects
Common: Flushing, sweating, hypotension, nausea, vomiting, somnolence, decreased deep tendon reflexes.
Serious: Respiratory depression, cardiac arrest, hypermagnesemia.
## Key Drug Interactions
* **Neuromuscular blockers:** Potentiates neuromuscular blockade.
* **Calcium channel blockers:** Increased risk of hypotension and bradycardia.
* **Tetracyclines and bisphosphonates:** Magnesium can decrease the absorption of these agents; separate administration by at least 2-4 hours.
## Monitoring
* **Serum magnesium levels:** Prior to and during therapy, especially with prolonged or high-dose infusions.
* **Renal function:** Assess baseline and monitor throughout therapy.
* **Vital signs:** Blood pressure, heart rate, respiratory rate.
* **Deep tendon reflexes:** Decreased reflexes can indicate rising magnesium levels.
* **Urine output:** Monitor for adequate renal function.
## Clinical Pearls
* Magnesium sulphate is a potent medication; IV administration requires careful monitoring.
* Rapid IV administration can cause flushing, sweating, and hypotension. Infuse slowly.
* Discontinue infusion if deep tendon reflexes diminish or respiratory rate falls below 16 breaths per minute.
* Always confirm the concentration and required elemental magnesium (mEq or mmol) for the ordered dose.
This information is intended for healthcare professionals. Always consult the current prescribing information and institutional protocols before administering any medication.
