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# Magnesium sulphate
## Overview
Magnesium sulphate is an essential electrolyte used for the treatment of hypomagnesemia, eclampsia, and refractory arrhythmias. It acts as a calcium antagonist and cofactor for many enzymatic reactions.
## Primary Indications
* **Hypomagnesemia:** Severe symptomatic deficiency.
* **Obstetrics:** Prevention of seizures in eclamptic/preeclamptic patients and fetal neuroprotection (preterm labor).
* **Cardiology:** Torsade de pointes (including drug-induced).
* **Pulmonology:** Adjunctive therapy for severe, refractory acute asthma exacerbations.
## Adult Dosing
* **Hypomagnesemia:** 1–4 g IV/IM. Common maintenance: 1 g/hour IV infusion for 6–12 hours.
* **Eclampsia (Preeclampsia):** Loading dose 4–6 g IV over 15–20 minutes, followed by 1–2 g/hour maintenance infusion.
* **Torsade de pointes:** 2 g IV bolus over 5–15 minutes.
* **Severe Asthma:** 2 g IV over 20 minutes (typically single dose).
## Pediatric Dosing
* **Hypomagnesemia:** 25–50 mg/kg/dose (max 2 g) IV/IM every 6 hours for 3–4 doses.
* **Asthma:** 25–50 mg/kg (max 2 g) IV over 20 minutes.
* **Note:** Dosing varies widely by institution; always consult local pediatric protocols and verify concentration.
## Dose Adjustments
* **Renal Impairment:** Reduce dose and frequency in patients with renal failure. Monitor serum magnesium closely; toxic drug accumulation occurs rapidly in patients with CrCl <30 mL/min.
## Contraindications
* Heart block (unless pacemaker present).
* Myocardial damage.
* Severe renal impairment (CrCl <20 mL/min) requires extreme caution/dose reduction.
## Adverse Effects
* **Dose-dependent:** Flushing, diaphoresis, hypotension, and bradycardia.
* **Toxic:** Loss of deep tendon reflexes (early sign), respiratory depression, cardiac arrest.
* **Hypermagnesemia:** Nausea, vomiting, confusion, EKG changes (prolonged PR, widened QRS).
## Key Drug Interactions
* **Neuromuscular Blockers:** Potentiates neuromuscular blockade.
* **CNS Depressants:** Enhances CNS depression (barbiturates, opioids).
* **Digitalis:** May precipitate digitalis toxicity if hypomagnesemia is corrected rapidly.
* **Calcium Channel Blockers:** Increases risk of hypotension and neuromuscular blockade.
## Monitoring
* **Clinical:** Assess patellar reflexes hourly (if on continuous infusion), respiratory rate (>12/min expected), and urine output (>30 mL/h).
* **Laboratory:** Serum magnesium (therapeutic range for eclampsia/asthma is often higher than homeostatic serum levels; consult protocol).
* **Antidote:** **Calcium gluconate** (1 g IV) should be immediately available at the bedside to treat respiratory depression or cardiac toxicity.
## Clinical Pearls
* Rapid IV administration can lead to hypotension and cardiac collapse; infusion pumps are mandatory for continuous drips.
* Serum levels do not always correlate with intracellular magnesium status.
* Ensure IV site patency; extravasation can cause local tissue injury.
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**Educational Disclaimer:** This information is for educational purposes only. Dosage, indications, and safety protocols can vary significantly based on local institutional guidelines and patient-specific factors. Always consult the latest package insert, official clinical guidelines, or your hospital’s pharmacy department before prescribing or administering medication.
