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# Magnesium Sulphate
## Overview
Magnesium sulphate is a parenteral mineral supplement used for electrolyte replacement, seizure prophylaxis, and as a smooth muscle relaxant. Pharmacokinetics are dependent on renal clearance.
## Primary Indications
* **Hypomagnesemia:** Correction of deficiency.
* **Eclampsia/Preeclampsia:** Seizure prophylaxis and treatment.
* **Torsades de Pointes:** Acute management of polymorphic ventricular tachycardia.
* **Asthma:** Adjunctive treatment for severe acute exacerbations.
## Adult Dosing
* **Hypomagnesemia (Mild):** 1–2 g IV/IM every 6 hours for 3–4 doses.
* **Hypomagnesemia (Severe, symptomatic):** 2–4 g IV over 10–60 minutes.
* **Eclampsia/Preeclampsia:** 4–6 g IV loading dose over 15–20 minutes, followed by a continuous infusion of 1–2 g/hour.
* **Torsades de Pointes:** 1–2 g IV bolus over 5–20 minutes, may repeat once.
* **Asthma (Severe):** 2 g IV single dose over 20 minutes.
## Pediatric Dosing
* **Hypomagnesemia:** 25–50 mg/kg/dose IV every 6 hours for 3–4 doses.
* **Asthma (Severe):** 25–75 mg/kg IV (max 2 g) over 20–30 minutes, usually as a single dose.
## Dose Adjustments
* **Renal Impairment:** Reduce dose by 50% or avoid if CrCl < 30 mL/min; use extreme caution in dialysis patients. Magnesium accumulates rapidly in renal failure.
## Contraindications
* Hypermagnesemia.
* Heart block or myocardial damage.
* Anuria/Severe renal impairment.
## Adverse Effects
* **Common:** Flushing, infusion-site pain, hypotension (transient).
* **Serious:** Respiratory depression (early sign: loss of patellar reflex), cardiac arrhythmias (hypotension, asystole), hypermagnesemia (lethargy, confusion).
## Key Drug Interactions
* **Neuromuscular Blockers:** Potentiates effect; risk of prolonged paralysis.
* **Calcium Channel Blockers:** May cause severe hypotension.
* **Digoxin:** Potential for increased digitalis toxicity risk if hypomagnesemia is corrected rapidly.
## Monitoring
* **Serum Magnesium:** Target physiologic range 1.7–2.3 mg/dL (varies by clinical context/ICU protocols).
* **Clinical:** Monitor deep tendon reflexes (DTRs), respiratory rate, and blood pressure before each dose/infusion rate change.
* **Renal:** Monitor urine output (maintain > 0.5 mL/kg/hr for eclampsia patients).
## Clinical Pearls
* **Toxicity Reversal:** Always have intravenous **Calcium Gluconate** (1 g) readily available at the bedside to reverse respiratory depression or cardiac toxicity associated with magnesium overdose.
* **Administration:** Rapid IV bolus can cause hypotension and cardiovascular collapse.
* **Local Protocol:** Dosing for eclampsia and severe asthma may vary significantly by facility/regional guidelines; always consult institutional order sets.
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*Disclaimer: This information is for educational purposes only. Dosing, contraindications, and monitoring parameters should be verified against current institutional policies, the patient's electronic health record, and official FDA-approved prescribing information.*
