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# Magnesium Sulphate
## Overview
Magnesium sulphate is an electrolyte that plays a crucial role in numerous physiological processes, including neuromuscular function, myocardial contractility, and enzyme activity.
## Primary Indications
* Hypomagnesemia
* Eclampsia and pre-eclampsia
* Torsades de pointes
* Bronchospasm (adjunctive therapy)
* Constipation (oral administration)
## Adult Dosing
**Hypomagnesemia:**
* **Intravenous (IV):**
* Treatment of acute deficiency: 4-5 grams IV infused over 5-60 minutes. May be followed by 1-2 grams/hour continuous infusion or intermittent doses of 1 gram every 4 hours as needed to maintain serum magnesium levels.
* Maintenance: Dosing varies based on serum magnesium levels and renal function. Typical maintenance infusion is 1-2 grams every 12-24 hours.
* **Intramuscular (IM):**
* Treatment of acute deficiency: 1 gram every 4 hours for 4 doses.
* **Oral:** Doses vary widely based on formulation and indication (e.g., laxative effect). Specific dosing depends on local protocol.
**Eclampsia/Pre-eclampsia:**
* Loading dose: 4-6 grams IV infused over 5 minutes.
* Maintenance infusion: 1-2 grams/hour. May be adjusted based on clinical response and magnesium levels.
* IM: 5 grams IM into each buttock (total 10 grams) for loading dose, followed by 5 grams IM every 4 hours.
**Torsades de Pointes:**
* 2 grams IV bolus, followed by continuous infusion of 1 gram/hour or as needed.
**Bronchospasm:**
* 1-2 grams IV infused over 15-30 minutes.
**Constipation:**
* Oral: Dose varies by formulation (e.g., Milk of Magnesia). Consult specific product information.
## Pediatric Dosing
Specific pediatric dosing often depends on local protocols and institutional guidelines.
**Hypomagnesemia:**
* **IV:**
* Loading dose: 25-50 mg/kg (0.1-0.2 mEq/kg) per dose, infused over 10-60 minutes. Maximum single dose generally 2 grams.
* Maintenance infusion: 20-30 mg/kg/day (0.1-0.15 mEq/kg/day) infused over 24 hours. May require higher doses in specific situations.
**Eclampsia/Seizures:**
* Follows adult protocols closely, but doses may be adjusted by weight and local guidelines.
## Dose Adjustments
* **Renal Impairment:** Magnesium is renally excreted. Reduce dose and monitor serum magnesium levels closely, especially in patients with moderate to severe renal impairment.
## Contraindications
* Hypermagnesemia
* Heart block
* Myocardial infarction
* Severe renal impairment (caution advised, dose reduction necessary)
* Hyperparathyroidism
* Addison's disease
## Adverse Effects
* **Common:** Flushing, sweating, hypotension, nausea, vomiting, decreased reflexes, somnolence.
* **Serious:** Respiratory depression, cardiac arrhythmias, cardiac arrest, hypermagnesemia (symptoms include absent deep tendon reflexes, ECG changes, hypotension, bradycardia, respiratory depression, coma).
## Key Drug Interactions
* **Neuromuscular Blockers:** Magnesium can potentiate the effects of neuromuscular blocking agents, leading to prolonged neuromuscular blockade.
* **Calcium Channel Blockers:** Additive hypotensive effects and increased risk of arrhythmias.
* **Tetracyclines and Quinolone Antibiotics:** Magnesium can decrease the absorption of these agents; administer at least 2 hours before or 4-6 hours after.
## Monitoring
* **Serum Magnesium Levels:** Essential, especially with IV administration or in renal impairment. Target levels depend on indication (e.g., for hypomagnesemia, typically 2-4 mEq/L; for eclampsia, typically 4-7 mEq/L).
* **Renal Function:** Monitor BUN and creatinine.
* **Deep Tendon Reflexes:** Loss of reflexes indicates approaching toxicity.
* **Respiratory Rate and Depth:** Monitor for signs of respiratory depression.
* **Blood Pressure:** Monitor for hypotension.
* **Cardiac Rhythm:** ECG monitoring may be indicated.
## Clinical Pearls
* Always dilute IV magnesium sulphate prior to infusion to reduce risk of local irritation and severe hypotension.
* Rapid IV infusion can cause flushing, diaphoresis, and hypotension.
* Discontinue magnesium infusion if deep tendon reflexes are lost, urine output is inadequate, or respiratory rate falls below 16 breaths/minute.
* Calcium gluconate or calcium chloride should be readily available as an antidote for magnesium toxicity.
* Oral magnesium formulations can cause diarrhea.
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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 local protocols for definitive guidance.
