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# Magnesium Sulfate
## Overview
Magnesium sulfate is an inorganic salt that acts as an electrolyte. It plays a crucial role in neuromuscular transmission, cardiac excitability, and enzyme activity.
## Primary Indications
* Treatment of hypomagnesemia
* Prevention and treatment of seizures in pre-eclampsia and eclampsia
* Management of torsades de pointes
* Bronchodilation in acute severe asthma (adjunctive therapy)
## Adult Dosing
* **Hypomagnesemia:**
* Severe (serum Mg < 1.3 mEq/L): 4-6 grams IV initially, followed by 1-2 grams/hour by continuous infusion. Duration depends on serum magnesium levels.
* Less Severe (serum Mg 1.3-1.7 mEq/L): 2 grams IV every 4-6 hours for 2-4 doses.
* Intramuscular: 1 gram IM every 6 hours for 4 doses (ensure adequate muscle mass, rotate sites).
* **Eclampsia/Pre-eclampsia:** 4-6 grams IV loading dose over 5-10 minutes, followed by a continuous infusion of 1-2 grams/hour. Alternative: 5 grams IM in each buttock (total 10g) as a loading dose, followed by 5 grams IM every 4 hours. Dosing can vary significantly based on local protocols.
* **Torsades de Pointes:** 1-2 grams IV in 50-100 mL D5W over 5-10 minutes. May repeat. Follow with a continuous infusion of 0.5-1 gram/hour.
* **Asthma (adjunctive):** 1-2 grams IV in 50-100 mL NS or D5W over 15-30 minutes.
## Pediatric Dosing
Dosing for pediatric patients is highly variable and depends on the indication and patient weight. It is essential to consult pediatric-specific guidelines or a pharmacist.
* **Hypomagnesemia:** Typically 25-50 mg/kg/dose IV or IM, up to a maximum of 2 grams per dose. May be followed by a continuous infusion.
* **Eclampsia/Pre-eclampsia:** Similar to adults, but precise dosing based on weight is crucial and varies by institution.
## Dose Adjustments
* **Renal Impairment:** Magnesium is renally excreted. Use with caution in patients with impaired renal function. Reduce dose and monitor serum magnesium levels closely. In severe renal impairment, avoid parenteral magnesium unless absolutely necessary and monitor very closely.
## Contraindications
* Hypermagnesemia
* Heart block
* Myocardial infarction (caution)
* Severe renal dysfunction
## Adverse Effects
* **Common:** Flushing, warmth, sweating, nausea, vomiting, hypotension, decreased reflexes, drowsiness.
* **Serious:** Respiratory depression, cardiac arrest, hypermagnesemia (symptoms include absent deep tendon reflexes, hypotension, bradycardia, ECG changes, respiratory arrest, cardiac arrest).
## Key Drug Interactions
* **Neuromuscular Blockers:** May potentiate neuromuscular blockade.
* **Calcium:** Calcium may antagonize the effects of magnesium.
* **Tetracyclines, Bisphosphonates:** Magnesium can decrease the absorption of oral tetracyclines and bisphosphonates. Separate administration by at least 2-4 hours.
## Monitoring
* **Serum Magnesium Levels:** Crucial, especially with IV infusions or in patients with renal impairment. Therapeutic range for hypomagnesemia treatment is typically 2.5-4.5 mEq/L.
* **Renal Function:** Monitor BUN and creatinine.
* **Vital Signs:** Blood pressure, heart rate, respiratory rate.
* **Deep Tendon Reflexes:** Assess for diminished or absent reflexes, a sign of toxicity.
* **Urine Output:** Indicates adequate renal perfusion.
* **ECG:** Especially in cardiac indications or if toxicity is suspected.
## Clinical Pearls
* When administering IV magnesium, monitor the patient closely for signs of toxicity. Have calcium gluconate readily available as an antidote.
* For IM administration, use large muscle masses and rotate injection sites. Pain and induration are common.
* Magnesium sulfate solutions are hypertonic and should be administered slowly to avoid phlebitis.
* In pre-eclampsia/eclampsia, continuous magnesium infusion is preferred for seizure prophylaxis after the loading dose.
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*Disclaimer: This information is intended for healthcare professionals. Always consult the most current prescribing information, institutional protocols, and patient-specific factors before making any treatment decisions.*
