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# Magnesium Sulfate
## Overview
Magnesium sulfate is an electrolyte that plays a vital role in numerous biochemical and physiological processes. It is a centrally acting skeletal muscle relaxant and anticonvulsant.
## Primary Indications
* Hypomagnesemia
* Preeclampsia and Eclampsia (seizure prophylaxis and treatment)
* Torsades de Pointes
* Asthma exacerbations (adjunctive therapy)
* Constipation (osmotic laxative)
## Adult Dosing
* **Hypomagnesemia:**
* **Severe (<1 mg/dL):** 4-6 g IV infusion over 5-60 minutes, followed by 1-2 g/hour infusion as needed.
* **Less severe:** 1-2 g IV/IM every 4-6 hours as needed.
* **Oral replacement:** 2.5-5 g of magnesium sulfate administered orally in 4-5 divided doses.
* **Preeclampsia/Eclampsia:**
* **Loading dose:** 4-6 g IV infusion over 5-20 minutes.
* **Maintenance infusion:** 1-2 g/hour IV infusion. Adjust based on clinical response and toxicity.
* **Torsades de Pointes:** 1-2 g IV bolus in 5% dextrose in water (D5W) over 5-10 minutes, followed by a continuous infusion of 0.5-1 g/hour.
* **Asthma Exacerbations:** 1-2 g IV infusion in 50-100 mL normal saline over 15-20 minutes.
* **Constipation:** 10-30 g orally as a single dose, taken with a full glass of water. Onset is typically 30 minutes to 6 hours.
## Pediatric Dosing
Dosing is often weight-based and may vary significantly by indication and institutional protocol. Consult specific pediatric guidelines.
* **Hypomagnesemia:** Typically 25-50 mg/kg/dose IV over 1-4 hours, not to exceed 2 g per dose. Maintenance infusions vary. Oral dosing varies.
* **Eclampsia:** Loading doses often 40 mg/kg IV, followed by maintenance infusions.
## Dose Adjustments
* **Renal Impairment:** Reduce dose and monitor serum magnesium levels closely. Magnesium is renally excreted. Dosage adjustments are not standardized and depend on the degree of renal impairment.
## Contraindications
* Hypermagnesemia
* Heart block greater than first degree (unless a pacemaker is present)
* Myocardial infarction
* Gastrointestinal obstruction (for oral administration)
* Anuria
## Adverse Effects
Common: Flushing, sweating, hypotension, nausea, vomiting, diarrhea (oral), decreased deep tendon reflexes, drowsiness, muscle weakness.
Serious: Respiratory depression, cardiac arrest, hypermagnesemia, hypothermia.
## Key Drug Interactions
* **Neuromuscular Blocking Agents:** Magnesium can potentiate neuromuscular blockade, increasing the risk of respiratory depression and prolonged paralysis.
* **Calcium Channel Blockers:** Additive hypotensive effects.
* **Antibiotics:** May interfere with absorption of tetracyclines and fluoroquinolones when given concurrently. Separate administration by at least 2 hours.
## Monitoring
* Serum magnesium levels (especially with IV infusions or renal impairment)
* Deep tendon reflexes
* Respiratory rate and depth
* Blood pressure
* Urine output
* ECG (for prolonged QT interval or cardiac arrhythmias)
## Clinical Pearls
* Magnesium sulfate is administered as a 50% solution (500 mg/mL). Ensure correct calculation of elemental magnesium.
* IM injections can be painful and should be given deep into a large muscle.
* Intravenous magnesium sulfate should be administered slowly to avoid adverse effects, particularly hypotension and flushing.
* For eclampsia, ensure the patient has adequate renal function and is receiving intravenous fluids. Continuous monitoring is crucial.
* Oral magnesium sulfate acts as an osmotic laxative; it should not be used in patients with intestinal obstruction or severe renal impairment.
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*This information is intended for healthcare professionals. Always consult the most current prescribing information and institutional protocols before administering any medication.*
