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# Magnesium Sulphate
## Overview
Magnesium sulfate is an electrolyte that plays a crucial role in numerous biochemical reactions in the body. It is available intravenously and intramuscularly for medical use.
## Primary Indications
* Treatment of hypomagnesemia
* Management of eclampsia and pre-eclampsia
* Treatment of torsades de pointes
* Adjunctive therapy in asthma exacerbations (off-label)
* Treatment of severe constipation (oral preparation, not typically used in acute care settings)
## Adult Dosing
Dosing is highly dependent on indication and patient status. Local protocols should be consulted.
* **Hypomagnesemia:**
* **Acute symptomatic:** 4-6 grams IV infused over 5-10 minutes, followed by 1-2 grams per hour via continuous infusion until symptoms resolve and serum magnesium levels normalize.
* **Chronic replacement:** Typically 1 gram IV or IM every 6 hours for 4 doses.
* **Eclampsia/Pre-eclampsia:**
* **Loading dose:** 4-6 grams IV infused over 15-20 minutes.
* **Maintenance infusion:** 1-2 grams per hour IV. Dosing adjusted based on clinical response and magnesium levels.
* **Torsades de Pointes:** 1-2 grams IV diluted in 10-50 mL D5W or NS, infused over 5-10 minutes. May repeat.
* **Asthma Exacerbation:** 1-2 grams IV diluted in 50-100 mL NS, infused over 15-30 minutes.
## Pediatric Dosing
Dosing is highly dependent on indication and patient status. Local protocols should be consulted.
* **Hypomagnesemia:** 25-50 mg/kg/dose IV infused over 30-60 minutes. Maximum single dose generally 2 grams. May repeat every 4-6 hours as needed.
* **Eclampsia/Pre-eclampsia:** Not typically used in pediatric patients for this indication.
* **Torsades de Pointes:** 25-50 mg/kg IV infused over 10-20 minutes. Maximum dose generally 2 grams.
## Dose Adjustments
* **Renal Impairment:** Magnesium is renally excreted. Reduce dose and monitor serum magnesium levels closely in patients with impaired renal function.
## Contraindications
* Hypermagnesemia
* Heart block (unless a pacemaker is present)
* Myocardial infarction (in certain contexts, especially if severe renal impairment)
* Myasthenia gravis (relative contraindication, use with caution)
* Known hypersensitivity to magnesium sulfate
## Adverse Effects
* **Common:** Flushing, sweating, hypotension, nausea, vomiting, decreased deep tendon reflexes.
* **Serious:** Respiratory depression, cardiac arrhythmias, cardiac arrest, hypermagnesemia (muscle weakness, lethargy, decreased reflexes, difficulty breathing, cardiac arrest).
## Key Drug Interactions
* **Nifedipine:** Increased risk of hypotension and neuromuscular blockade.
* **Neuromuscular Blocking Agents:** Increased risk of prolonged neuromuscular blockade.
* **Aminoglycosides:** Potential for additive neuromuscular blockade.
* **Calcium Salts:** May antagonize the effects of magnesium; administer separately.
## Monitoring
* **Serum Magnesium Levels:** Monitor frequently, especially during infusion and in patients with renal impairment. Target levels vary by indication.
* **Renal Function:** Assess baseline and monitor.
* **Vital Signs:** Blood pressure, heart rate, respiratory rate.
* **Deep Tendon Reflexes:** Assess for loss of reflexes, which indicates hypermagnesemia.
* **Urine Output:** Monitor for adequate renal function.
* **ECG:** Consider if cardiac effects are suspected.
## Clinical Pearls
* Always dilute magnesium sulfate prior to IV infusion. Rapid IV administration can cause hypotension, flushing, and cardiac arrest.
* Monitor for signs of hypermagnesemia, especially in patients with renal impairment or those receiving high doses. Loss of deep tendon reflexes is an early sign.
* Ensure calcium gluconate is readily available as an antidote for severe hypermagnesemia.
* In eclampsia, monitor fetal heart rate closely.
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**Disclaimer:** This information is for educational purposes only and does not substitute for professional medical advice. Always consult the most current prescribing information and guidelines, and consider individual patient factors before making any treatment decisions.
