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# Magnesium sulphate
## Overview
Magnesium sulphate is a concentrated electrolyte primarily utilized for critical care conditions. It acts as a calcium antagonist and cofactor in numerous enzymatic reactions. Available as IV infusion (most common) or IM injection.
## Primary Indications
* **Hypomagnesemia:** Correction of deficiency.
* **Torsades de Pointes/Arrhythmias:** Acute management of refractory ventricular arrhythmias.
* **Eclampsia/Preeclampsia:** Prevention and control of seizures.
* **Severe Asthma:** Adjunctive therapy for acute, refractory exacerbations.
## Adult Dosing
* **Hypomagnesemia:** 1–4 g (8–32 mEq) IV over 4–60 minutes. Mild cases may use 1–2 g; severe/symptomatic cases require faster infusion (e.g., 2 g over 15 minutes).
* **Torsades de Pointes:** 2 g IV bolus over 5–15 minutes, followed by a continuous infusion of 3–20 mg/min as needed.
* **Eclampsia/Preeclampsia:** 4–6 g IV loading dose over 15–20 minutes, followed by 1–2 g/hr continuous maintenance infusion.
* **Severe Asthma:** 2 g IV bolus over 20 minutes as a one-time dose.
## Pediatric Dosing
* **Hypomagnesemia:** 25–50 mg/kg/dose IV/IM every 4–6 hours as needed (Max: 2 g/dose).
* **Severe Asthma:** 25–50 mg/kg/dose IV (Max: 2 g) administered over 20 minutes.
* *Note: Always verify pediatric dosing against local institutional protocols (e.g., Harriet Lane).*
## Dose Adjustments
* **Renal Impairment:** Reduce dose and frequency in patients with CrCl <30 mL/min or elevated serum creatinine. Accumulation risk is high; monitor levels strictly.
## Contraindications
* Heart block (unless pacemaker present).
* Myocardial damage.
* Severe renal impairment (if used at high doses).
* Avoid within 2 hours of delivery in patients with eclampsia if possible (monitor neonate for neuro/respiratory depression).
## Adverse Effects
* **Common:** Flushing, hypothermia, diaphoresis.
* **Serious (Dose-dependent):** Hypotension, bradycardia, respiratory depression, loss of deep tendon reflexes (DTRs), AV block, cardiac arrest.
## Key Drug Interactions
* **Neuromuscular Blockers:** Potentiates effect; risk of prolonged paralysis.
* **Aminoglycosides:** May potentiate neuromuscular blockade.
* **Calcium Channel Blockers:** Enhances risk of hypotension and heart block.
* **Digoxin:** Increased risk of toxicity if magnesium is used for arrhythmias.
## Monitoring
* **Safety Thresholds:** Monitor DTRs (patellar reflex should be present), respiratory rate (>12/min), and urine output (>30 mL/hr).
* **Serum Levels:** Monitor baseline and periodically thereafter. Therapeutic range for preeclampsia: 4–7 mEq/L (or 4.8–8.4 mg/dL).
* **ECG:** Monitor for widening QRS or prolonged PR interval.
* **Antidote:** Keep 10% Calcium Gluconate at bedside to reverse magnesium toxicity.
## Clinical Pearls
* **Administration:** Concentrated solutions (e.g., 50%) must be diluted for IV use to prevent vein irritation.
* **Safety:** Always double-check infusion pump settings; rapid IV push can cause cardiac arrest.
* **Preeclampsia:** If using for seizure prophylaxis, absent patellar reflexes are often the first clinical sign of toxicity before respiratory arrest.
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**Disclaimer:** This information is for educational purposes only. Always consult your institution’s clinical guidelines, medication package inserts, or a qualified pharmacist to verify dosing, compatibility, and safety before prescribing or administering medication.
