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# Magnesium Sulphate
## Overview
Magnesium sulphate is an essential mineral that plays a crucial role in various physiological processes, including neuromuscular function, cardiac rhythm, and enzyme activity.
## Primary Indications
* Treatment of hypomagnesemia.
* Management of eclampsia and pre-eclampsia.
* Treatment of severe asthma exacerbations (off-label, often used adjunctively).
* Management of torsades de pointes.
## Adult Dosing
* **Hypomagnesemia:**
* **Mild:** 1 gram (8 mEq) intramuscularly (IM) or intravenously (IV) every 6 hours for 4 doses.
* **Severe:** 4 grams (32 mEq) IV infusion over 1 hour, followed by an infusion of 1-2 grams (8-16 mEq) per hour as needed, guided by serum magnesium levels and clinical response. Dosing depends on the degree of deficiency and can range from 16 to 40 mEq over several hours.
* **Eclampsia/Pre-eclampsia:**
* **Loading Dose:** 4-6 grams IV infusion over 5-20 minutes.
* **Maintenance Infusion:** 1-2 grams per hour IV. Dosing may vary based on local protocols and institutional guidelines. A typical regimen is 4g IV loading followed by 1g/hr IV maintenance for 24 hours after the last seizure or delivery.
* **Torsades de Pointes:** 1-2 grams (8-16 mEq) IV in 10-20 mL of D5W over 5-10 minutes. Repeat if necessary.
* **Asthma (Adjunctive):** 1-2 grams IV infusion over 15-30 minutes.
## Pediatric Dosing
* **Hypomagnesemia:** Dosing is highly variable and depends on serum magnesium levels. A common initial IV dose is 25-50 mg/kg (0.1-0.2 mEq/kg) per dose, infused over 1-2 hours. Maximum single dose typically 2 grams (16 mEq). Further doses and infusion rates are guided by serum magnesium concentrations.
* **Eclampsia/Pre-eclampsia:** Not typically used in pediatric patients.
* **Torsades de Pointes:** 25-50 mg/kg (0.1-0.2 mEq/kg) IV as a single dose, infused over 10-20 minutes. Maximum single dose typically 2 grams (16 mEq).
* **Asthma (Adjunctive):** 25-50 mg/kg IV infusion over 15-30 minutes. Maximum dose typically 2 grams.
## Dose Adjustments
No specific dose adjustments are typically required for hepatic impairment. Dose reduction may be considered in severe renal impairment due to the risk of accumulation. Monitor serum magnesium levels closely.
## Contraindications
* Hypermagnesemia.
* Heart block (unless a pacemaker is present).
* Myocardial infarction.
* Pulmonary edema.
* Shock.
* Severe renal failure.
## Adverse Effects
Common adverse effects include flushing, sweating, nausea, vomiting, and hypotension. More serious adverse effects with rapid IV infusion or overdose include:
* **Neuromuscular blockade:** Decreased deep tendon reflexes, muscle weakness, paralysis.
* **Cardiovascular:** Hypotension, bradycardia, cardiac arrest, ECG changes.
* **Respiratory:** Respiratory depression.
* **Central nervous system:** Drowsiness, lethargy, confusion.
## Key Drug Interactions
* **Neuromuscular Blockers:** Magnesium sulphate can potentiate the effects of neuromuscular blocking agents.
* **Calcium Channel Blockers:** Increased risk of hypotension and bradycardia.
* **Tetracyclines and Bisphosphonates:** Magnesium can decrease the absorption of these agents. Administer these drugs at least 2 hours before or 4-6 hours after magnesium sulphate.
* **Nifedipine:** Concurrent use in eclampsia has been associated with severe hypotension and muscle weakness.
## Monitoring
* Serum magnesium levels (especially with IV infusions or in renal impairment).
* Deep tendon reflexes.
* Respiratory rate and depth.
* Blood pressure and heart rate.
* Urine output.
* ECG (especially with high doses or in cardiac disease).
## Clinical Pearls
* Magnesium sulphate should be administered slowly to avoid adverse effects. Rapid IV infusion can lead to hypotension, flushing, and cardiorespiratory depression.
* The antidote for magnesium toxicity is intravenous calcium (e.g., calcium gluconate).
* In patients with renal insufficiency, monitor magnesium levels closely as accumulation can occur.
* Ensure calcium gluconate is readily available when administering magnesium sulphate, especially IV.
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*This information is intended for healthcare professionals. Always consult the most current prescribing information and institutional protocols for definitive guidance.*
