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# Magnesium sulfate
## Overview
Magnesium sulfate is an essential electrolyte used for the treatment of hypomagnesemia, preeclampsia/eclampsia, and as an adjunctive agent for refractory bronchospasm or arrhythmias. It acts as a calcium antagonist and neuromuscular blocker.
## Primary Indications
* Hypomagnesemia
* Eclampsia and severe preeclampsia (seizure prophylaxis)
* Torsades de pointes (with or without cardiac arrest)
* Refractory status asthmaticus
* Preterm labor (neuroprotection, though off-label and varies by institutional protocol)
## Adult Dosing
* **Hypomagnesemia:** 1–4 g IV/IM. Common emergency regimen: 2 g IV over 15–60 minutes.
* **Torsades de Pointes/Cardiac Arrest:** 1–2 g IV push (over 5–20 minutes); may repeat once.
* **Eclampsia/Preeclampsia:** 4–6 g IV loading dose over 15–20 minutes, followed by 1–2 g/hr continuous IV infusion.
* **Asthma:** 2 g IV over 20 minutes (typically single dose adjunct).
## Pediatric Dosing
* **Hypomagnesemia:** 25–50 mg/kg/dose IV/IM; max 2 g per dose.
* **Torsades de Pointes:** 25–50 mg/kg IV/IO; max 2 g per dose.
* **Status Asthmaticus:** 25–50 mg/kg IV over 20 minutes; max 2 g per dose.
## Dose Adjustments
* **Renal Impairment:** Reduce dose or increase interval in patients with CrCl <30 mL/min. Magnesium accumulates rapidly in renal failure; monitor serum levels closely. Use with extreme caution.
## Contraindications
* Heart block (unless pacemaker present)
* Myocardial damage
* Severe renal impairment (CrCl < 20 mL/min)
* Hypersensitivity
## Adverse Effects
* **Common:** Flushing, sweating, hypotension, transient hypotension.
* **Serious:** Respiratory depression (early sign: loss of deep tendon reflexes), bradycardia, heart block, cardiac arrest, hypocalcemia.
## Key Drug Interactions
* **Neuromuscular Blockers:** Potentiates effect (e.g., vecuronium, rocuronium).
* **Calcium Channel Blockers:** May enhance hypotension.
* **Digoxin:** Use caution; magnesium may exacerbate digitalis toxicity signs.
* **Aminoglycosides:** Potential for additive respiratory depression.
## Monitoring
* **Serum Magnesium:** Targeted range 1.7–2.3 mg/dL (or higher depending on indication).
* **Clinical Signs:** Monitor deep tendon reflexes (DTRs), respiratory rate, and urine output (maintain >0.5 mL/kg/hr).
* **Antidote:** Calcium gluconate (1 g IV) must be immediately available for magnesium toxicity.
## Clinical Pearls
* **Infusion Rates:** Rapid administration can induce profound hypotension and asystole.
* **Reflexes:** If patellar reflexes disappear, suspect hypermagnesemia; hold maintenance infusion immediately and check serum levels.
* **Local Variability:** Administration protocols for obstetrics and status asthmaticus are highly institution-specific; always verify against local guidelines.
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**Educational Disclaimer:** This information is for educational purposes only. Clinical practice varies by institution and patient presentation. Always verify dosages and protocols with current institutional guidelines, electronic health records, or the drug manufacturer's prescribing information before administration.
