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# Magnesium Sulfate
## Overview
Magnesium sulfate is an electrolyte that plays a crucial role in various cellular functions, including nerve impulse transmission and muscle contraction.
## Primary Indications
* Treatment and prevention of hypomagnesemia.
* Management of eclampsia and pre-eclampsia.
* Treatment of torsades de pointes.
* Adjunctive therapy for severe asthma exacerbations (less common).
## Adult Dosing
* **Hypomagnesemia:**
* **Mild deficiency:** 1 gram IV/IM every 6 hours for 4 doses.
* **Severe deficiency/Torsades de Pointes:** 1-4 grams IV infused over 5-60 minutes. Subsequent doses may be 1-2 grams per hour as needed.
* **Maintenance:** 4-6 grams added to 1000 mL of IV fluid daily.
* **Eclampsia/Pre-eclampsia (Prophylaxis and Treatment):**
* **Loading dose:** 4-6 grams IV infused over 5-20 minutes.
* **Maintenance infusion:** 1-2 grams per hour IV. Dosing may vary based on local protocol and patient response.
## Pediatric Dosing
Dosing in pediatrics is highly variable and often guided by serum magnesium levels and clinical indication. It is typically weight-based.
* **Hypomagnesemia:**
* **IV:** 20-50 mg/kg/dose (as anhydrous magnesium sulfate) infused over 10-15 minutes. Maximum dose typically 2 grams.
* **IM:** 25-50 mg/kg/dose (as anhydrous magnesium sulfate). Maximum dose typically 2 grams.
* **Eclampsia (Adjunctive):** Pediatric dosing is not well established and should be guided by specialist consultation and local protocols.
## Dose Adjustments
* **Renal Impairment:** Magnesium is renally excreted. In patients with renal impairment, reduce the dose and monitor serum magnesium levels closely. Use with caution and consider reduced doses in moderate to severe renal impairment.
## Contraindications
* Hypermagnesemia.
* Hypersensitivity to magnesium sulfate.
* Heart block.
* Myocardial infarction with impending heart failure.
* Anuria.
## Adverse Effects
Common: Flushing, sweating, hypotension, nausea, vomiting, decreased deep tendon reflexes, somnolence.
Serious: Respiratory depression, cardiac arrest, hypermagnesemia (especially in renal impairment), decreased urine output.
## Key Drug Interactions
* **Neuromuscular Blockers:** Magnesium can potentiate neuromuscular blockade, increasing the risk of prolonged muscle paralysis.
* **Calcium:** Calcium administration may antagonize the cardiac effects of magnesium.
* **Tetracyclines and Bisphosphonates:** Oral magnesium may decrease the absorption of these medications. Separate administration by at least 2 hours.
## Monitoring
* **Serum magnesium levels:** Frequently monitor, especially with IV infusions and in patients with renal impairment. Target levels vary by indication.
* **Renal function (BUN, creatinine):** Assess baseline and periodically.
* **Vital signs:** Blood pressure, heart rate, respiratory rate.
* **Deep tendon reflexes:** Assess for depression, which can indicate toxicity.
* **Urine output:** Monitor for adequate renal excretion.
* **ECG:** In patients receiving high doses or with cardiac concerns.
## Clinical Pearls
* Magnesium sulfate is a high-alert medication. Double-check doses and infusion rates.
* Rapid IV infusion can cause hypotension and cardiac dysfunction. Infuse as recommended.
* Hypermagnesemia can present with symptoms similar to hypocalcemia.
* For IM administration, use a 20-gauge or larger needle and inject deeply into the buttock. Do not exceed 2 mL in one IM site.
* When treating hypomagnesemia, assess for and correct hypokalemia and hypocalcemia, as these can coexist and exacerbate magnesium deficiency symptoms.
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*Disclaimer: This information is intended for clinical professionals. Always verify the most current prescribing information with the official product labeling and institutional protocols.*
