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# Magnesium Sulphate
## Overview
Magnesium sulphate is a parenteral mineral supplement used for anticonvulsant therapy, neuromuscular stabilization, and management of life-threatening arrhythmias.
## Primary Indications
* **Eclampsia/Pre-eclampsia:** Prevention and treatment of seizures.
* **Torsades de Pointes:** Management of polymorphic ventricular tachycardia.
* **Status Asthmaticus:** Adjunctive therapy for severe acute exacerbations.
* **Hypomagnesemia:** Treatment of symptomatic deficiency.
## Adult Dosing
* **Eclampsia:** 4–6 g IV loading dose over 15–20 minutes, followed by 1–2 g/hour continuous infusion.
* **Torsades de Pointes (with pulse):** 1–2 g IV/IO over 5–20 minutes.
* **Status Asthmaticus:** 2 g IV over 20 minutes as a single dose.
* **Severe Hypomagnesemia:** 1–4 g IV over 1–4 hours; may repeat as needed based on serum levels.
## Pediatric Dosing
* **Status Asthmaticus:** 25–75 mg/kg IV (max 2 g) over 20 minutes.
* **Hypomagnesemia (Acute):** 25–50 mg/kg/dose IV; may repeat every 6 hours for 3–4 doses.
* *Note:* Pediatric dosing is highly variable; institutional protocols must be consulted.
## Dose Adjustments
* **Renal Impairment:** Reduce dosage and frequency in patients with renal insufficiency (CrCl <30 mL/min). Monitor serum magnesium levels closely; avoid doses exceeding 20 g per 48 hours unless serum levels are monitored.
## Contraindications
* Myasthenia gravis (may precipitate respiratory crisis).
* Heart block.
* Severe renal impairment (except in emergency settings).
* Hypersensitivity to magnesium products.
## Adverse Effects
* **Common:** Flushing, infusion site pain, sweating, nausea.
* **Serious:** Hypotension, respiratory depression, bradycardia, complete heart block, cardiac arrest.
* **Toxicity:** Loss of deep tendon reflexes (first sign of hypermagnesemia, typically at 7–10 mEq/L).
## Key Drug Interactions
* **Neuromuscular Blockers:** Potentiates the effects of non-depolarizing agents.
* **CNS Depressants:** May cause additive respiratory/CNS depression.
* **Digoxin:** Concurrent use may increase the risk of cardiac conduction disturbances.
* **Aminoglycosides:** Risk of increased neuromuscular blockade.
## Monitoring
* **Reflexes:** Patellar reflex check hourly (loss of reflex precedes respiratory arrest).
* **Respiratory Rate:** Monitor continuously (maintain >12–16 breaths/min).
* **Urine Output:** Maintain >0.5 mL/kg/hr in obstetric patients (magnesium is renally excreted).
* **Serum Levels:** Monitor 2–4 hours after initiation or with renal impairment. Target range for pre-eclampsia: 4–8 mg/dL (1.7–3.3 mmol/L).
* **Antidote:** **Calcium Gluconate** (e.g., 1 g IV) should be immediately available at the bedside to treat severe respiratory depression or cardiac toxicity.
## Clinical Pearls
* **Extravasation:** Ensure proper IV line placement; concentrate infusion to prevent phlebitis.
* **Renal Clearance:** Magnesium toxicity is almost exclusively associated with accumulation in renally impaired patients receiving continuous infusions.
* **Practice Variation:** Dosing protocols for pre-eclampsia and asthma are highly institution-specific; always verify against local guidelines.
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*Disclaimer: This information is for educational purposes only. Always consult current institutional protocols, official prescribing information (package insert), and clinical pharmacist support before prescribing or administering medication.*
