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# Magnesium Sulphate
## Overview
Magnesium sulphate is an essential mineral used to treat and prevent hypomagnesemia and for its tocolytic, anticonvulsant, and bronchodilator properties. It is available for intravenous (IV) and intramuscular (IM) administration.
## Primary Indications
* Treatment of hypomagnesemia.
* Prevention of hypomagnesemia in specific patient populations (e.g., alcohol withdrawal, malnutrition).
* Tocolysis to inhibit premature labor.
* Prevention and treatment of seizures in preeclampsia and eclampsia.
* Status asthmaticus.
## Adult Dosing
Dosing varies significantly based on indication. Consult institutional protocols or specific guidelines for precise dosing.
* **Hypomagnesemia (Severe):**
* **Loading Dose:** 4-6 grams IV infused over 5-15 minutes, followed by a continuous infusion.
* **Maintenance Infusion:** 1-2 grams per hour IV, adjusted based on serum magnesium levels.
* **IM Dosing:** 1 gram IM every 4 hours for 4 doses (use Z-track method). Maximum daily IM dose is typically 30-40 grams.
* **Tocolysis:** Typically 4-6 grams IV loading dose followed by a maintenance infusion of 1-4 grams per hour IV.
* **Preeclampsia/Eclampsia:**
* **Loading Dose:** 4-6 grams IV infused over 5-20 minutes.
* **Maintenance Infusion:** 1-2 grams per hour IV.
* **IM Dosing:** 5 grams IM in each buttock (total 10g) initially, followed by 5 grams IM every 4 hours.
* **Status Asthmaticus:** 1-2 grams IV infused over 15-30 minutes.
## Pediatric Dosing
Pediatric dosing is complex and depends on indication, weight, and clinical status. Consult specialized pediatric references or guidelines.
* **Hypomagnesemia:** Dosing varies widely. For example, a common IV maintenance dose may range from 100-200 mg/kg/day divided into 4 doses, with loading doses calculated based on current and desired magnesium levels. Maximum doses are critical.
* **Eclampsia:** Similar to adults, though specific pediatric protocols exist.
## Dose Adjustments
* **Renal Impairment:** Magnesium is renally excreted. Use with caution and monitor serum magnesium levels closely. Dose reduction and/or increased monitoring interval is necessary in patients with impaired renal function.
## Contraindications
* Hypermagnesemia.
* Heart block.
* Myocardial infarction (caution advised).
* Severe renal impairment.
* Myasthenia gravis (caution advised, can worsen neuromuscular blockade).
* Bowel obstruction or perforation (for oral magnesium).
## Adverse Effects
Common: Flushing, sweating, hypotension, nausea, vomiting, decreased reflexes, drowsiness.
Serious: Respiratory depression, cardiac arrhythmias, cardiac arrest, neuromuscular blockade, hypermagnesemia.
## Key Drug Interactions
* **Neuromuscular Blockers (e.g., rocuronium, vecuronium):** Magnesium can potentiate neuromuscular blockade, increasing the risk of prolonged paralysis and respiratory depression.
* **Calcium Channel Blockers:** Additive hypotensive effects and potential for increased cardiac depression.
* **Tetracyclines and Fluoroquinolones:** Magnesium can decrease the absorption of these antibiotics; administer at least 2 hours before or 4-6 hours after magnesium.
* **Digoxin:** Hypermagnesemia can increase digoxin toxicity.
## Monitoring
* **Serum Magnesium Levels:** Crucial for guiding therapy, especially with IV infusions. Therapeutic range typically 2.0-3.5 mEq/L (or 4.0-7.0 mg/dL) for severe hypomagnesemia/eclampsia, though goals may vary.
* **Renal Function:** Monitor BUN and creatinine.
* **Deep Tendon Reflexes:** Assess for signs of hypermagnesemia (loss of reflexes).
* **Respiratory Rate and Effort:** Monitor for respiratory depression.
* **Blood Pressure and Heart Rate:** Monitor for hypotension and arrhythmias.
* **Urine Output:** Monitor for adequate renal function.
## Clinical Pearls
* Magnesium sulphate infusions can cause flushing, warmth, and transient hypotension. Administer IV infusions slowly and monitor vital signs.
* Loss of deep tendon reflexes is an early sign of magnesium toxicity.
* Always ensure adequate hydration and renal function before administering magnesium, especially IV.
* In eclampsia, magnesium sulphate is the drug of choice for seizure prophylaxis and treatment.
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**Disclaimer:** This information is intended for healthcare professionals and is not a substitute for professional medical advice. Always consult the most current prescribing information and institutional protocols before administering any medication.
