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# Magnesium sulfate
## Overview
Magnesium sulfate is an essential electrolyte used for the treatment of hypomagnesemia, eclampsia, and as an adjunct in cardiac arrhythmias. It acts as a physiologic calcium channel blocker and cofactor for enzymatic processes.
## Primary Indications
* Hypomagnesemia
* Eclampsia/Preeclampsia (seizure prophylaxis and treatment)
* Torsades de pointes (pulmonary edema/ventricular arrhythmias)
* Refractory status asthmaticus (adjunct)
## Adult Dosing
* **Hypomagnesemia:** 1–4 g IV/IM. Common regimen: 2 g IV over 15–60 minutes. Severe deficit may require 1–2 g/hr infusion.
* **Torsades de pointes:** 2 g IV push over 5–15 minutes, followed by infusion if necessary.
* **Eclampsia/Preeclampsia:** 4–6 g IV loading dose over 15–20 minutes, followed by 1–2 g/hr continuous infusion. (Refer to Zuspan or Parkland protocols).
* **Severe Asthma:** 2 g IV infusion over 15–20 minutes.
## Pediatric Dosing
* **Hypomagnesemia:** 25–50 mg/kg/dose IV/IM every 6 hours for 3–4 doses. Maximum: 2 g/dose.
* **Status Asthmaticus:** 25–75 mg/kg IV (max 2 g) infused over 20 minutes.
* **Arrhythmia:** 25–50 mg/kg IV (max 2 g) over 10–20 minutes.
## Dose Adjustments
* **Renal Impairment:** Reduce dose or increase interval in patients with serum creatinine >1.5 mg/dL or CrCl <30 mL/min. Magnesium accumulates rapidly in renal failure.
## Contraindications
* Heart block
* Myocardial damage
* Severe renal impairment (unless strictly monitored)
* Recent myocardial infarction
## Adverse Effects
* **Common:** Flushing, sweating, hypotension, warmth.
* **Serious (Magnesium Toxicity):** Loss of deep tendon reflexes (early sign), respiratory depression, bradycardia, AV block, cardiac arrest.
* **Antidote:** Calcium gluconate 1 g IV should be available at the bedside for rapid reversal of toxic effects.
## Key Drug Interactions
* **Neuromuscular Blockers:** Potentiates effect (risk of respiratory paralysis).
* **Aminoglycosides:** Potentiates neuromuscular blockade.
* **CNS Depressants:** May increase sedative effects.
* **Digitalis:** Use with extreme caution; may cause cardiac conduction disturbances.
## Monitoring
* **Serum Magnesium:** Maintain therapeutic range (typically 1.7–2.3 mg/dL for asymptomatic status; 4–7 mEq/L for preeclampsia).
* **Physical:** Deep tendon reflexes (DTRs), respiratory rate (must be >12 breaths/min), and urine output (at least 30 mL/hr).
* **ECG:** Monitor for PR interval prolongation or QRS widening.
## Clinical Pearls
* **Always** recheck DTRs before subsequent doses of infusion. Absent DTRs are the first clinical indicator of impending toxic magnesium levels.
* **Safety:** Magnesium sulfate is a high-alert medication. Ensure proper concentration labeling to avoid lethal dose errors.
* **Compatibility:** Highly dependent on local protocol; verify pharmacy compatibility charts before Y-site administration, as magnesium can precipitate with certain drugs.
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*Disclaimer: This information is for educational purposes only. Always consult current institutional protocols and the full prescribing information (package insert) before ordering or administering medications.*
