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# Magnesium Sulfate
## Overview
Magnesium sulfate is an essential mineral. It plays a vital role in numerous biochemical reactions, including neuromuscular transmission and muscle contraction.
## Primary Indications
* Treatment of hypomagnesemia.
* Prevention and treatment of seizures in preeclampsia and eclampsia.
* Management of status epilepticus refractory to other agents.
* Treatment of torsades de pointes.
* Adjunctive therapy in severe asthma exacerbations.
## Adult Dosing
* **Hypomagnesemia:**
* **Severe symptomatic (e.g., seizures, arrhythmias):** 4 to 6 grams IV infused over 5 to 60 minutes, followed by a maintenance infusion of 1 to 2 grams per hour. Dosing may need to be adjusted based on serum magnesium levels and clinical response.
* **Asymptomatic/less severe:** 1 to 2 grams IM or IV every 6 to 12 hours for 3 to 4 doses.
* **Preeclampsia/Eclampsia:** Loading dose of 4 to 6 grams IV infused over 5 to 20 minutes, followed by a maintenance infusion of 1 to 2 grams per hour. Alternative: 5 grams IM in each buttock (10 grams total) for loading, followed by 5 grams IM every 4 hours.
* **Torsades de Pointes:** 1 to 2 grams IV infused over 5 to 20 minutes. May repeat as needed.
* **Status Epilepticus (refractory):** 1 to 2 grams IV infused over 5 to 20 minutes.
* **Asthma Exacerbation:** 1 to 2 grams IV infused over 15 to 30 minutes.
Dosing for hypomagnesemia is highly variable and should be guided by serum magnesium levels and patient response. Specific protocols may exist at local institutions.
## Pediatric Dosing
* **Hypomagnesemia:** Dosing varies significantly by age and weight. Commonly used regimens range from 20 to 100 mg/kg/dose (elemental magnesium) IV over 30 minutes to 4 hours, with subsequent doses or infusions guided by serum magnesium levels. Maximum single dose typically not to exceed 2 grams.
* **Status Epilepticus:** 25 to 100 mg/kg/dose (elemental magnesium) IV, up to a maximum single dose of 2 grams.
* **Preeclampsia:** Not typically used in pediatric patients.
Pediatric dosing is complex and requires careful calculation and monitoring. Consult pediatric-specific guidelines or a pediatric pharmacist.
## Dose Adjustments
* **Renal Impairment:** Magnesium is renally excreted. In patients with significant renal impairment, doses should be reduced, and serum magnesium levels closely monitored to prevent accumulation and toxicity.
## Contraindications
* Hypermagnesemia.
* Heart block (unless a pacemaker is in place).
* Myocardial infarction (use with caution and only when indicated).
* Hypersensitivity to magnesium sulfate.
## Adverse Effects
* **Common:** Flushing, sensation of heat, hypotension, nausea, vomiting, drowsiness, decreased deep tendon reflexes, respiratory depression.
* **Severe:** Cardiac arrest, cardiac conduction abnormalities, muscle weakness, absent deep tendon reflexes, hyperreflexia (if overdose), severe respiratory depression, coma.
## Key Drug Interactions
* **Neuromuscular Blockers:** Magnesium can potentiate neuromuscular blockade, leading to prolonged muscle relaxation and respiratory depression.
* **Calcium:** Calcium may antagonize the effects of magnesium.
* **Tetracyclines and Quinolones:** Magnesium can decrease the absorption of these antibiotics; administer at least 2 hours before or 6 hours after magnesium.
* **Bisphosphonates:** Magnesium can decrease absorption; separate administration.
* **CNS Depressants:** Additive CNS depressant effects.
## Monitoring
* **Serum Magnesium Levels:** Essential for guiding therapy, especially with IV infusions. Therapeutic range for hypomagnesemia is typically 1.7 to 2.2 mmol/L (4.1 to 5.3 mg/dL), but may be higher for seizure prophylaxis in preeclampsia.
* **Renal Function (BUN, Creatinine):** To assess the need for dose adjustments.
* **Vital Signs:** Blood pressure, heart rate, respiratory rate.
* **Deep Tendon Reflexes:** A decrease or loss of reflexes indicates excessive magnesium levels.
* **Urine Output:** Monitor for adequacy.
* **ECG:** Particularly if concerns for cardiac effects arise.
## Clinical Pearls
* Intravenous magnesium sulfate can cause transient flushing and a feeling of warmth.
* Rapid IV infusion can lead to hypotension and cardiac arrhythmias. Infuse slowly as recommended.
* Monitor deep tendon reflexes closely. Loss of reflexes is an early sign of magnesium toxicity.
* Ensure adequate calcium stores and renal function before initiating high-dose magnesium therapy.
* When treating hypomagnesemia, aim for a serum magnesium level between 1.7-2.2 mmol/L (4.1-5.3 mg/dL). Higher levels may be targeted for seizure prevention in preeclampsia.
* Magnesium sulfate is available in various concentrations; always verify the concentration and calculate the dose based on elemental magnesium.
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*This information is intended for healthcare professionals and does not replace current prescribing information. Always verify the most up-to-date drug information with official sources.*
