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# Magnesium Sulfate
## Overview
Magnesium sulfate is an electrolyte that is essential for normal muscle and nerve function, blood glucose control, and blood pressure regulation. It is available in intravenous (IV) and intramuscular (IM) formulations.
## Primary Indications
* Hypomagnesemia
* Preeclampsia and eclampsia (seizure prophylaxis and treatment)
* Torsades de Pointes
* Bronchospasm (adjunctive therapy in severe cases)
* Constipation (oral formulation)
## Adult Dosing
* **Hypomagnesemia:**
* **Acute severe:** 4-5 grams IV infused over 5-60 minutes, followed by 1-2 grams/hour infusion for up to 24 hours. Alternatively, 1 gram IM every 4 hours for 4 doses.
* **Less severe:** 1 gram IV bolus, then 1 gram/hour infusion.
* Dosing adjusted based on serum magnesium levels and patient's renal function.
* **Preeclampsia/Eclampsia:**
* **Loading dose:** 4-5 grams IV infused over 5 minutes, or 5 grams IM (2.5 grams in each buttock) if IV access is not readily available.
* **Maintenance infusion:** 1-2 grams/hour IV infusion.
* Regimens can vary; consult local protocol.
* **Torsades de Pointes:** 1-2 grams IV diluted in 10-20 mL D5W, infused over 5-10 minutes. May repeat. Further infusion at 0.5-1 gram/hour may be considered.
* **Bronchospasm (adjunctive):** 2 grams IV diluted in 50-100 mL saline, infused over 20 minutes.
* **Constipation:** Oral magnesium citrate solutions (e.g., 10 oz) or magnesium hydroxide suspensions (e.g., 30-60 mL).
## Pediatric Dosing
* **Hypomagnesemia:** Dosing is weight-based and depends on severity. Typical doses range from 25-100 mg/kg/dose IV or IM, not to exceed 2 grams per dose, with subsequent doses adjusted based on serum magnesium. Consult specialized pediatric resources for precise dosing.
* **Eclampsia:** Dosing follows adult protocols, but caution is advised due to immature renal function. Consult specialized pediatric resources.
* **Bronchospasm (adjunctive):** 25-50 mg/kg/dose IV, maximum 2 grams/dose, infused over 30 minutes.
## Dose Adjustments
* **Renal Impairment:** Magnesium is renally excreted. Reduce dose and monitor serum magnesium levels closely in patients with impaired renal function. Avoid in severe renal failure unless absolutely necessary and with close monitoring.
## Contraindications
* Hypermagnesemia
* Heart block greater than first degree
* Myocardial infarction (unless coexisting severe hypomagnesemia)
* Shock
* Severe renal impairment (caution)
## Adverse Effects
* **Common:** Flushing, sweating, nausea, vomiting, hypotension, decreased deep tendon reflexes.
* **Serious:** Respiratory depression, cardiac arrhythmias, cardiac arrest, hypermagnesemia (especially with renal impairment).
## Key Drug Interactions
* **Neuromuscular Blocking Agents:** Magnesium can potentiate neuromuscular blockade, increasing the risk of prolonged paralysis.
* **Calcium Channel Blockers:** Additive hypotensive effects and potential for severe bradycardia or heart block.
* **Tetracyclines and Quinolones:** Magnesium can decrease the absorption of these antibiotics; administer at least 2 hours before or 4-6 hours after.
* **Digoxin:** High doses of magnesium can increase digoxin toxicity.
## Monitoring
* Serum magnesium levels (pre-treatment, periodically during infusion, and as clinically indicated)
* Renal function (BUN, creatinine)
* Deep tendon reflexes
* Respiratory rate and depth
* Blood pressure
* Urine output
* ECG (if indicated)
## Clinical Pearls
* IV magnesium sulfate should be administered in a monitored setting due to the risk of cardiorespiratory depression and hypermagnesemia.
* Always dilute IV magnesium sulfate before administration.
* IM injections can be painful and should be given in divided doses in different muscle sites.
* Monitor for signs of magnesium toxicity, especially in patients with renal impairment or receiving concurrent medications that affect neuromuscular transmission.
* Oral magnesium preparations are generally used for constipation and have a different absorption profile and risk of toxicity compared to parenteral formulations.
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**Disclaimer:** This information is intended for healthcare professionals. Always consult the most current official prescribing information and relevant clinical guidelines for complete and up-to-date details before making any clinical decisions. Dosing and protocols may vary based on institutional guidelines and individual patient circumstances.
