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# Magnesium Sulfate
## Overview
Magnesium sulfate is an electrolyte that plays a crucial role in numerous enzymatic reactions and physiological processes. It is available for intravenous (IV) and intramuscular (IM) administration.
## Primary Indications
* Treatment of hypomagnesemia
* Management of eclampsia and pre-eclampsia
* Treatment of torsades de pointes
* Management of status asthmaticus (adjunctive therapy)
* Management of severe bronchospasm (adjunctive therapy)
## Adult Dosing
* **Hypomagnesemia:**
* **Severe (serum magnesium < 1 mg/dL):** 4-6 grams IV infused over 5-60 minutes, followed by a continuous infusion of 2-3 grams/hour for up to 24 hours. Alternatively, 1 gram IM every 6 hours for 4 doses.
* **Mild to moderate (serum magnesium 1-1.5 mg/dL):** 2-4 grams IV infused over 1-2 hours.
* **Eclampsia/Pre-eclampsia:** Loading dose: 4-6 grams IV infused over 5-20 minutes. Maintenance dose: 1-2 grams/hour IV infusion. Maximum dose typically 40 grams in 24 hours.
* **Torsades de Pointes:** 1-2 grams IV in 50-100 mL D5W over 5-10 minutes. May repeat. Followed by continuous infusion of 0.5-1 gram/hour.
* **Status Asthmaticus/Severe Bronchospasm:** 1-2 grams IV infused over 15-30 minutes.
## Pediatric Dosing
* **Hypomagnesemia:** Dosing is highly variable and depends on the severity of deficiency and patient weight. Typical doses range from 25-100 mg/kg/dose IV/IM, often divided and infused over several hours. Followed by maintenance infusions. Specific protocols should be followed.
* **Eclampsia (adjunctive to seizure management):** Dosing can be similar to adults (e.g., 4 grams IV loading dose). Maintenance infusions may be used. Pediatric guidelines should be consulted.
* **Status Asthmaticus/Severe Bronchospasm:** 25-100 mg/kg IV infused over 15-30 minutes. Maximum dose typically 2 grams.
## Dose Adjustments
* **Renal Impairment:** Magnesium is renally excreted. In patients with impaired renal function, reduce the dose and monitor serum magnesium levels closely. Use with caution in moderate to severe renal impairment.
## Contraindications
* Myasthenia gravis
* Heart block
* Hypermagnesemia
* Known hypersensitivity to magnesium sulfate
## Adverse Effects
Common: Flushing, hypotension, somnolence, nausea, vomiting, decreased deep tendon reflexes.
Serious: Respiratory depression, cardiac arrest, hypermagnesemia (especially in renal impairment).
## Key Drug Interactions
* **Neuromuscular blocking agents:** May potentiate neuromuscular blockade.
* **Calcium:** May antagonize the cardiac and CNS depressant effects of magnesium.
* **Nifedipine:** Potential for additive hypotension and myocardial depression.
* **Tetracyclines and bisphosphonates:** Reduced absorption if administered concurrently due to chelation. Separate administration by at least 2-3 hours.
## Monitoring
* **Serum magnesium levels:** Monitor frequently, especially during loading doses and continuous infusions, and in patients with renal impairment. Target levels vary by indication.
* **Renal function:** Assess baseline and monitor.
* **Vital signs:** Blood pressure, heart rate, respiratory rate.
* **Deep tendon reflexes:** Assess for loss of reflexes, which can indicate toxicity.
* **Urine output:** Monitor for adequate renal function.
* **ECG:** Especially in patients with cardiac conditions or receiving high doses.
## Clinical Pearls
* Magnesium sulfate is a potent vasodilator and can cause hypotension; infuse IV doses slowly.
* Rapid IV infusion can cause flushing, sweating, and a burning sensation.
* Signs of magnesium toxicity include decreased deep tendon reflexes, hypotension, bradycardia, respiratory depression, and cardiac arrest. Calcium gluconate is the antidote.
* When administering IV infusions, ensure adequate IV access and monitoring equipment are available.
* For IM administration, divide doses between two sites due to potential for local irritation.
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**Disclaimer:** This information is for educational purposes only and does not substitute for professional medical advice. Always consult the most current prescribing information and guidelines from regulatory agencies and professional organizations before making any treatment decisions. Dosing may vary based on institutional protocols.
