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# Magnesium sulfate
## Overview
Magnesium sulfate is an essential mineral used for electrolyte replenishment, seizure prevention, and as an adjunctive agent in respiratory and cardiovascular therapy. It acts as a physiological calcium antagonist and neuromuscular blocker.
## Primary Indications
* **Hypomagnesemia:** Correction of deficiency.
* **Eclampsia/Preeclampsia:** Prevention and treatment of seizures.
* **Torsades de Pointes/Arrhythmias:** Management of life-threatening ventricular arrhythmias.
* **Severe Asthma:** Adjunctive therapy for acute exacerbations.
* **Preterm Labor:** Historically used for tocolysis; now primarily for fetal neuroprotection.
## Adult Dosing
* **Hypomagnesemia (Mild):** 1–2 g IV or IM every 4–6 hours as needed.
* **Hypomagnesemia (Severe symptomatic):** 1–4 g IV over 5–60 minutes; may follow with a continuous infusion (e.g., 0.5–1 g/hour) for maintenance.
* **Eclampsia/Preeclampsia:** Loading dose of 4–6 g IV over 15–20 minutes, followed by 1–2 g/hour continuous infusion. Maintain for 24 hours postpartum.
* **Torsades de Pointes:** 2 g IV bolus over 5–15 minutes; may repeat once if rhythm persists.
* **Acute Asthma:** 2 g IV infusion over 20 minutes.
## Pediatric Dosing
* **Hypomagnesemia:** 25–50 mg/kg/dose IV/IM every 4–6 hours as needed; max 2 g/dose.
* **Acute Asthma:** 25–75 mg/kg IV infusion over 20 minutes; max 2 g/dose.
* **Arrhythmias:** 25–50 mg/kg IV bolus over 10–20 minutes; max 2 g.
## Dose Adjustments
* **Renal Impairment:** Reduce dose in patients with renal insufficiency (CrCl <30 mL/min). Monitor serum magnesium levels frequently; risk of toxicity is significantly increased.
## Contraindications
* Heart block or myocardial damage.
* Severe renal impairment (CrCl <20 mL/min).
* Recent myocardial infarction.
* Avoid use within 2 hours of delivery if possible unless treating eclampsia/neuroprotection.
## Adverse Effects
* **Early signs of toxicity:** Loss of deep tendon reflexes (DTRs), flushing, hypotension, diaphoresis.
* **Severe toxicity:** Respiratory depression, cardiac arrest, AV block, paralysis.
* **Injection site:** Local irritation/pain upon administration.
## Key Drug Interactions
* **CNS Depressants:** May cause additive respiratory depression.
* **Neuromuscular Blockers:** Potentiates the effects; may cause prolonged paralysis.
* **Calcium Channel Blockers:** Increased risk of severe hypotension and neuromuscular blockade.
* **Digoxin:** Use caution; magnesium may alter cardiac conduction.
## Monitoring
* **Serum Magnesium:** Maintain therapeutic range (typically 1.5–2.5 mg/dL for replenishment; 4–7 mEq/L or 4.8–8.4 mg/dL for eclampsia).
* **Clinical Signs:** Assess DTRs (the first clinical sign of hypermagnesemia is loss of patellar reflex), respiratory rate (>12-16 breaths/min), and urine output (>30 mL/hour).
* **Antidote:** Keep **Calcium Gluconate 1g IV** readily available at the bedside to treat respiratory depression or cardiac toxicity.
## Clinical Pearls
* **Administration:** Rapid IV push can cause hypotension and cardiac collapse; infusion rates should be controlled.
* **Neuroprotection:** Magnesium sulfate for fetal neuroprotection (preterm delivery <32 weeks) is a widely accepted practice; consult local obstetrical protocols for specific transition to postpartum monitoring.
* **Renal Function:** Always confirm adequate urine output before and during continuous infusions, as magnesium is renally excreted.
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**Educational Disclaimer:** This information is for educational purposes only. Drug dosing, indications, and safety protocols can vary significantly by clinical setting and institutional policy. Always verify specific doses and administration guidelines with the most current pharmacy database (e.g., Lexicomp, Micromedex) or your institution’s clinical protocols before prescribing or administering medication.
