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# Magnesium Sulphate
## Overview
Magnesium sulphate is an electrolyte that plays a vital role in numerous physiological processes, including neuromuscular function, cardiac rhythm, and bone metabolism. It is available in parenteral and oral formulations.
## Primary Indications
* Treatment of hypomagnesemia.
* Management of eclampsia and pre-eclampsia.
* Treatment of torsades de pointes.
* Management of status epilepticus refractory to standard therapy.
* Use as a bronchodilator in severe asthma exacerbations.
## Adult Dosing
* **Hypomagnesemia:**
* Severe (serum Mg < 1.3 mEq/L or 0.65 mmol/L): 4-6 grams IV infused over 5-60 minutes, followed by 1-2 grams/hour as a continuous infusion. Total daily dose not to exceed 16-20 grams.
* Mild to moderate: 1-2 grams IV or IM every 4-6 hours for 4 doses, or 1 gram orally every 6 hours.
* **Eclampsia/Pre-eclampsia:** Loading dose: 4-6 grams IV infused over 5-10 minutes. Maintenance: 1-2 grams/hour IV infusion. Alternatively, 5 grams IM in each buttock. Local protocols may vary.
* **Torsades de Pointes:** 1-2 grams IV in 50-100 mL D5W over 5-10 minutes. May repeat dose if needed. Continuous infusion of 0.5-1 gram/hour may be considered.
* **Status Epilepticus (refractory):** 2-4 grams IV infused over 10-20 minutes.
* **Severe Asthma Exacerbation:** 1-2 grams IV infused over 15-30 minutes.
## Pediatric Dosing
* **Hypomagnesemia:** 25-50 mg/kg/dose IV or IM every 4-6 hours for 4 doses. Maximum single dose typically 2 grams.
* **Eclampsia/Pre-eclampsia:** Dosing varies and is often guided by institutional protocols. A common regimen includes a loading dose of 40 mg/kg (maximum 2 grams) IV followed by an infusion of 20 mg/kg/hour.
* **Status Epilepticus (refractory):** 25-100 mg/kg IV infused over 10-20 minutes. Maximum dose typically 2 grams.
* **Asthma:** 25-40 mg/kg IV infused over 15-30 minutes. Maximum dose typically 2 grams.
## Dose Adjustments
* **Renal Impairment:** Magnesium is renally excreted. Use with caution and reduce dose in patients with renal impairment. Monitor magnesium levels closely.
## Contraindications
* Hypermagnesemia.
* Heart block.
* Myocardial infarction with cardiac compromise.
* Hyperkalemia.
* Intestinal obstruction or perforation (for oral formulations).
## Adverse Effects
Common: Flushing, hypotension, nausea, vomiting, diarrhea (oral).
Serious: Respiratory depression, cardiac arrest, loss of deep tendon reflexes, muscle weakness, somnolence, confusion.
## Key Drug Interactions
* **Neuromuscular blockers (e.g., succinylcholine, rocuronium):** Potentiates neuromuscular blockade, increasing the risk of prolonged respiratory depression.
* **Calcium channel blockers:** May potentiate hypotension.
* **Nifedipine:** Additive hypotensive effects.
* **Digoxin:** High doses of IV magnesium can potentiate digoxin toxicity.
* **Tetracyclines and bisphosphonates:** Oral magnesium can decrease the absorption of these medications; separate administration by at least 2 hours.
## Monitoring
* Serum magnesium levels (especially with IV infusions and in renal impairment).
* Renal function (BUN, creatinine).
* Deep tendon reflexes.
* Respiratory rate and effort.
* Blood pressure.
* Urine output.
* ECG for prolonged QT interval or arrhythmias.
## Clinical Pearls
* Rapid IV infusion can cause hypotension and flushing. Infuse slowly.
* Magnesium sulphate is an antidote for torsades de pointes, even in the absence of hypomagnesemia.
* Monitor for signs of magnesium toxicity, especially in patients with impaired renal function.
* Oral magnesium can cause diarrhea, limiting its use for chronic supplementation.
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*Disclaimer: This information is intended for healthcare professionals. Always consult the most current prescribing information and institutional protocols before administering any medication.*
