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# Magnesium Sulphate
## Overview
Magnesium sulfate is an electrolyte that plays a vital role in numerous biochemical processes. It is administered intravenously or intramuscularly as a replacement therapy for magnesium deficiency and for its therapeutic effects in specific conditions.
## Primary Indications
* Hypomagnesemia
* Eclampsia and severe preeclampsia
* Torsades de Pointes
* Bronchodilator in severe asthma exacerbations (adjunctive therapy)
## Adult Dosing
Dosing is highly individualized based on magnesium levels and clinical indication. Protocols may vary.
* **Hypomagnesemia:**
* **Severe (serum Mg < 1.0 mEq/L or 0.5 mmol/L):** 4-6 grams IV infused over 5-60 minutes, followed by a continuous infusion of 1-2 grams/hour for up to 24 hours or until serum magnesium stabilizes.
* **Mild to moderate (serum Mg 1.0-1.5 mEq/L or 0.5-0.75 mmol/L):** 2-4 grams IV infused over 1-3 hours, followed by maintenance infusion as needed.
* **Intramuscular (IM):** 1-2 grams every 4-6 hours for 3-4 doses, typically for less severe cases or when IV access is challenging.
* **Eclampsia/Preeclampsia:** Loading dose of 4-6 grams IV over 5-20 minutes, followed by a maintenance infusion of 1-2 grams/hour. Adjustments based on seizure recurrence and magnesium levels.
* **Torsades de Pointes:** 1-2 grams IV in 10-20 mL D5W over 5-10 minutes. May repeat if necessary. Follow with infusion of 2 grams in 500 mL D5W at 1 mg/min.
* **Asthma (adjunctive):** 1-2 grams IV over 15-20 minutes.
## Pediatric Dosing
Dosing is weight-based and often guided by specific institutional protocols.
* **Hypomagnesemia:** Typical dose is 25-50 mg/kg/dose IV over 10-60 minutes. Maximum single dose usually 2 grams. Maintenance infusions vary significantly. IM administration also used.
* **Eclampsia:** Less common in pediatrics. Protocols may adapt adult dosing.
* **Torsades de Pointes:** 25-50 mg/kg IV over 10-20 minutes. Maximum 2 grams. May repeat.
## Dose Adjustments
* **Renal Impairment:** Magnesium is renally excreted. Reduce dose and monitor serum magnesium levels closely, especially in moderate to severe renal dysfunction. Avoid in severe renal failure if possible.
## Contraindications
* Hypermagnesemia
* Heart block greater than first degree
* Myocardial infarction (caution)
* Anuria or severe renal dysfunction (relative contraindication, requires significant dose reduction and monitoring)
## Adverse Effects
* **Common:** Flushing, sweating, hypotension, nausea, vomiting, decreased deep tendon reflexes, drowsiness.
* **Serious:** Respiratory depression, cardiac arrhythmias, cardiac arrest, hypermagnesemia (especially with renal impairment).
## Key Drug Interactions
* **Neuromuscular Blocking Agents:** Magnesium can potentiate neuromuscular blockade, leading to prolonged respiratory depression.
* **Calcium Channel Blockers:** Additive hypotensive effects.
* **Tetracyclines and Quinolones:** Magnesium can impair absorption. Separate administration by at least 2-3 hours.
* **Digoxin:** Increased risk of digoxin toxicity with hypermagnesemia.
## Monitoring
* **Serum Magnesium Levels:** Crucial, especially with infusions. Target levels vary by indication (e.g., 2-4 mEq/L or 1-2 mmol/L for eclampsia).
* **Renal Function (BUN, Creatinine):** Essential due to renally excreted nature.
* **Deep Tendon Reflexes:** Monitor for signs of magnesium toxicity.
* **Respiratory Rate and Effort:** Assess for respiratory depression.
* **Blood Pressure and Heart Rate:** Monitor for hypotension and arrhythmias.
* **Urine Output:** Indicator of renal perfusion and function.
## Clinical Pearls
* Always dilute magnesium sulfate for IV infusion to prevent phlebitis and reduce risk of adverse effects.
* Administer IV infusions slowly to avoid hypotension and hypermagnesemia.
* Monitor vital signs and reflexes closely during administration.
* Have calcium gluconate readily available as an antidote for magnesium toxicity.
* Consider the patient's underlying renal function before initiating or continuing magnesium therapy.
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*Please verify this information against the most current prescribing information and institutional protocols.*
