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# Magnesium sulfate
## Overview
Magnesium sulfate is an essential electrolyte used for the treatment of hypomagnesemia and specific obstetric and neurological conditions. It acts as a physiological calcium antagonist and neuromuscular blocking agent.
## Primary Indications
* **Hypomagnesemia:** Replacement therapy.
* **Obstetrics:** Prevention/control of seizures in eclampsia and preeclampsia; fetal neuroprotection (preterm labor).
* **Cardiovascular:** Management of life-threatening ventricular arrhythmias (e.g., Torsades de Pointes).
* **Respiratory:** Adjunctive therapy for severe acute asthma.
## Adult Dosing
* **Hypomagnesemia (Mild):** 1–4 g IM or IV infusion over 1–4 hours.
* **Hypomagnesemia (Severe/Symptomatic):** 2–4 g IV bolus over 5–15 minutes, followed by 5–10 g infusion over 24 hours.
* **Eclampsia/Preeclampsia:** Loading dose of 4–6 g IV over 15–30 minutes, followed by maintenance infusion of 1–2 g/hour (protocol-dependent; maintain serum Mg 4–7 mEq/L).
* **Torsades de Pointes:** 1–2 g IV push over 5–15 minutes.
* **Severe Acute Asthma:** 2 g IV infusion over 20 minutes as a one-time dose.
## Pediatric Dosing
* **Hypomagnesemia:** 25–50 mg/kg/dose IM or IV (slow infusion). Max single dose 2 g.
* **Status Asthmaticus:** 25–50 mg/kg IV infusion over 20 minutes (max 2 g).
* **Note:** Always verify specific pediatric institutional protocols, as concentrations and infusion rates vary significantly by age and indication.
## Dose Adjustments
* **Renal Impairment:** Requires dose reduction and increased monitoring. Avoid if CrCl < 30 mL/min or exercise caution with bolus-only dosing; maintain serum levels closely.
## Contraindications
* Myasthenia gravis (may precipitate respiratory crisis).
* Severe renal impairment (CrCl < 20 mL/min for infusion).
* Heart block or myocardial damage (use with extreme caution).
* Hypermagnesemia.
## Adverse Effects
* **Expected/Early:** Flushing, sweating, hypotension, transient hypotension, depressed reflexes.
* **Severe:** Respiratory depression, cardiac conduction abnormalities (prolonged PR/QRS/QT), complete heart block, circulatory collapse, hypocalcemia.
* **Antidote:** Calcium gluconate (or calcium chloride) 1 g IV.
## Key Drug Interactions
* **Neuromuscular Blockers:** Potentiates effect; use caution with succinylcholine or other non-depolarizing agents.
* **Aminoglycosides:** Potential for additive neuromuscular blockade.
* **Digitalis Glycosides:** Risk of arrhythmias if rapid changes in serum magnesium occur.
## Monitoring
* **Clinical:** Patellar reflex (absence suggests early toxicity), respiratory rate (>12-16 breaths/min required), urine output (>30 mL/hour).
* **Laboratory:** Serum magnesium levels (Therapeutic range: 1.7–2.2 mg/dL for routine, up to 4–7 mEq/L for preeclampsia).
## Clinical Pearls
* **Safety:** Always calculate infusion rates carefully; rapid IV bolus can cause hypotension or asystole.
* **Administration:** Ensure a calcium source is immediately available at the bedside for rapid reversal of toxic effects.
* **Dosing Variability:** Many protocols for Obstetrics and Asthma are institutional-specific; verify local standard of care before ordering.
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**Educational Disclaimer:** This information is for educational purposes only. Always verify drug doses, contraindications, and monitoring requirements against current local guidelines, institutional protocols, and official manufacturer prescribing information prior to administration.
