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# Magnesium Sulphate
## Overview
Magnesium sulphate is a parenteral mineral supplement used for anticonvulsant activity in eclampsia, antiarrhythmic effects in specific tachyarrhythmias, and as an adjunctive treatment for severe bronchospasm. Mechanism involves blocking neuromuscular transmission and decreasing acetylcholine release.
## Primary Indications
* **Eclampsia/Preeclampsia:** Prevention and control of seizures.
* **Torsades de Pointes:** Treatment of drug-induced or hypomagnesemic arrhythmias.
* **Severe Acute Asthma:** Adjunctive therapy for bronchodilation unresponsive to standard treatment.
* **Hypomagnesemia:** Replacement therapy (severe symptomatic).
## Adult Dosing
* **Eclampsia:** Loading dose: 4–6 g IV over 15–20 minutes. Maintenance: 1–2 g/hour by continuous IV infusion.
* **Torsades de Pointes/Cardiac Arrest:** 1–2 g IV/IO over 5–20 minutes (push for pulseless patients).
* **Severe Asthma:** 2 g IV over 20 minutes as a single dose.
* **Severe Hypomagnesemia:** 1–4 g IM/IV; dose and rate vary based on urgency and local protocol.
## Pediatric Dosing
* **Severe Asthma:** 25–75 mg/kg (max 2 g) IV infused over 20 minutes.
* **Hypomagnesemia:** 25–50 mg/kg/dose every 4–6 hours for 3–4 doses; may repeat if indicated.
* **Status Asthmaticus:** Seek institutional guidelines; typically reserved for PICU settings.
## Dose Adjustments
* **Renal Impairment:** Reduce dose in renal failure (CrCl <30 mL/min). Clinical guidelines vary; monitor serum magnesium frequently. Risk of accumulation and toxicity is high.
## Contraindications
* Myasthenia gravis (due to worsening of neuromuscular blockade).
* Heart block or myocardial damage.
* Severe renal impairment (unless specific criteria met under strict monitoring).
## Adverse Effects
* **Common:** Flushing, sweating, hypotension, transient hypotension.
* **Serious (Toxicity):** Loss of deep tendon reflexes (early sign), respiratory depression, cardiac arrest, AV block.
* **Note:** Calcium gluconate is the antidote for magnesium toxicity.
## Key Drug Interactions
* **Neuromuscular Blocking Agents:** Potentiates effect (increased risk of paralysis).
* **CNS Depressants:** May increase sedation/respiratory depression.
* **Aminoglycosides:** May enhance neuromuscular blockade.
* **Digoxin:** Use with caution; may aggravate heart block.
## Monitoring
* **Serum Magnesium Levels:** Maintain target range (e.g., 4–7 mEq/L for eclampsia).
* **Clinical Signs:** Evaluate deep tendon reflexes (patellar reflex), respiratory rate (>12 breaths/min), and urine output (>30 mL/hr) prior to each maintenance dose in eclampsia.
* **ECG:** Monitor for conduction disturbances during rapid infusion.
## Clinical Pearls
* Rapid administration (IV push) can cause respiratory collapse and hypotension; infuse over 15–20+ minutes except in cardiac arrest.
* Always ensure calcium gluconate (1 g) is immediately available at the bedside whenever magnesium sulphate is infusing.
* Dosages are highly context-dependent; always consult institutional protocols/order sets (e.g., OB/peds/ICU) for specific titration parameters.
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**Educational Disclaimer:** This information is for educational purposes only. Clinical practice varies by institution. Consult the current package insert and your hospital’s latest clinical guidelines or pharmacy department before prescribing or administering medication.
