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# Magnesium Sulphate
## Overview
Magnesium sulphate is an essential mineral involved in numerous biochemical functions. It is available in oral and parenteral formulations.
## Primary Indications
* Hypomagnesemia
* Preeclampsia/Eclampsia (intravenous)
* Torsades de Pointes (intravenous)
* Constipation (oral, osmotic laxative)
* Asthma exacerbations (intravenous, adjunctive therapy)
## Adult Dosing
* **Hypomagnesemia:**
* **Severe (<1.0 mEq/L):** 4-6 grams IV infused over 5-60 minutes, followed by a continuous infusion of 2-4 grams/hour for up to 24 hours.
* **Less Severe (>1.0 mEq/L):** 1-4 grams IV infused over 5-60 minutes.
* Oral repletion: 2-4 grams orally per day in divided doses.
* **Preeclampsia/Eclampsia:** 4-6 grams IV loading dose over 5-20 minutes, followed by a maintenance infusion of 1-2 grams/hour. Higher doses may be required in eclampsia. Specific protocols vary.
* **Torsades de Pointes:** 1-2 grams IV in 10 mL D5W over 5-10 minutes. Repeat if necessary. Can also be given as an infusion.
* **Constipation:** 10-30 grams orally as a single dose. Onset is typically 30 minutes to 6 hours.
* **Asthma Exacerbations (Adjunctive):** 1-2 grams IV infused over 15-30 minutes.
## Pediatric Dosing
* **Hypomagnesemia:**
* **Severe (<1.0 mEq/L):** 25-50 mg/kg IV (elemental magnesium) infused over 5-15 minutes. Max 2 grams. May repeat every 4 hours. Maintenance infusion: 20-30 mg/kg/day IV (elemental magnesium).
* **Less Severe (>1.0 mEq/L):** 25-50 mg/kg IV (elemental magnesium) infused over 5-15 minutes. Max 2 grams.
* Oral repletion: Dosing is less established and depends on age and weight; consult specific pediatric guidelines.
* **Eclampsia (Adjunctive):** Pediatric dosing is not well-established; consult specialist literature or local protocols.
* **Asthma Exacerbations (Adjunctive):** 25-40 mg/kg IV (elemental magnesium) infused over 15-30 minutes. Max 2 grams.
## Dose Adjustments
* **Renal Impairment:** Use with extreme caution. Reduce dose and monitor magnesium levels closely. Avoid in severe renal failure if possible.
## Contraindications
* Hypermagnesemia
* Heart block
* Myocardial infarction (in the setting of acute MI, though sometimes used for torsades)
* Bowel obstruction (oral)
* Anuria (oral)
* Rectal bleeding (oral)
## Adverse Effects
* **Parenteral:** Flushing, hypotension, bradycardia, respiratory depression, CNS depression, hyperthermia, diaphoresis, hyporeflexia.
* **Oral:** Diarrhea, abdominal cramping, nausea.
## Key Drug Interactions
* **Neuromuscular Blockers:** Potentiates neuromuscular blockade.
* **Tetracyclines and Quinolones:** Magnesium can decrease absorption; separate administration by at least 2-4 hours.
* **Digoxin:** Increased risk of digoxin toxicity in hypermagnesemia.
* **Calcium Salts:** May antagonize the effects of magnesium.
## Monitoring
* Serum magnesium levels (especially with parenteral administration, renal impairment, or prolonged therapy)
* Renal function (creatinine)
* Deep tendon reflexes (for signs of hypermagnesemia)
* Respiratory rate and depth
* Blood pressure
* Cardiac rhythm
## Clinical Pearls
* IV magnesium can cause flushing and a feeling of warmth.
* Monitor urine output as an indicator of renal perfusion and to assess for potential toxicity.
* In preeclampsia/eclampsia, consider calcium gluconate readily available for reversal of toxicity.
* Oral magnesium sulphate is an osmotic laxative; ensure adequate hydration.
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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. Dosage and indications can vary.
