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# Magnesium Sulfate
## Overview
Magnesium sulfate is an electrolyte that plays a crucial role in numerous biochemical reactions, including neuromuscular transmission and muscle contraction. It is available for intravenous and intramuscular administration.
## Primary Indications
* Treatment of hypomagnesemia.
* Management of seizures in preeclampsia and eclampsia.
* Treatment of torsades de pointes.
* Management of status asthmaticus.
## Adult Dosing
* **Hypomagnesemia:**
* **Severe deficiency (<1 mg/dL):** 4 to 6 g IV infused over 1 to 4 hours, followed by 1 to 2 g IV or IM every 4 to 6 hours as needed.
* **Less severe deficiency (1-1.5 mg/dL):** 2 g IV or IM over 5 to 30 minutes, followed by 1 g IV or IM every 4 to 6 hours for 3 to 4 doses.
* Alternatively, a continuous infusion of 1 to 2 g/hour may be used.
* **Preeclampsia/Eclampsia:** Loading dose of 4 to 6 g IV infused over 5 to 10 minutes, followed by a maintenance infusion of 1 to 2 g/hour. IM administration: 5 g IM into each buttock (total 10 g) within 1 hour, followed by 5 g IM every 4 hours. Local protocols often dictate specific dosing and duration.
* **Torsades de Pointes:** 1 to 2 g IV in 10 mL of D5W over 5 to 10 minutes. May repeat dose. Further infusion of 0.5 to 1 g/hour may be necessary.
* **Status Asthmaticus:** 25 to 50 mg/kg IV, maximum dose 2 g, infused over 15 to 30 minutes.
## Pediatric Dosing
* **Hypomagnesemia:** 25 to 50 mg/kg IV or IM every 4 to 6 hours for 3 to 4 doses. Maximum single dose 2 g.
* **Eclampsia:** Dosing is complex and often based on adult guidelines adapted for weight, or specific institutional protocols. A common approach is a loading dose of 40 mg/kg (max 4 g) IV over 5-10 minutes, followed by an infusion of 5-15 mg/kg/hr (max 1 g/hr).
* **Status Asthmaticus:** 25 to 50 mg/kg IV infused over 15 to 30 minutes. Maximum dose 2 g.
## 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.
## Contraindications
* Hypermagnesemia.
* Heart block.
* Myocardial infarction.
* Renal failure (absolute contraindication for IV administration in severe cases, caution in mild to moderate).
* Myasthenia gravis.
## Adverse Effects
Common adverse effects include flushing, hypotension, nausea, vomiting, and somnolence. More serious effects include respiratory depression, cardiac arrhythmias, loss of deep tendon reflexes, and hypermagnesemia (muscle weakness, decreased reflexes, hypotension, bradycardia, cardiac arrest).
## Key Drug Interactions
* **Neuromuscular Blockers:** Magnesium can potentiate neuromuscular blockade, leading to prolonged muscle weakness or respiratory depression.
* **Calcium:** High doses of magnesium can interfere with calcium absorption and may antagonize the effects of calcium.
* **Tetracyclines and Quinolones:** Magnesium may decrease the absorption of these antibiotics. Administer at least 2 hours before or 4-6 hours after.
## Monitoring
* **Serum magnesium levels:** Especially important in patients with renal impairment and during prolonged infusions. Target levels typically range from 2 to 3.5 mg/dL for hypomagnesemia and 4 to 7 mEq/L (2 to 3.5 mmol/L) for eclampsia.
* **Renal function (BUN, creatinine).**
* **Deep tendon reflexes:** Loss of reflexes may indicate hypermagnesemia.
* **Respiratory rate and depth.**
* **Blood pressure.**
* **Cardiac rhythm.**
## Clinical Pearls
* Rapid IV infusion can cause hypotension and cardiac depression. Administer IV infusions slowly.
* IM injections can be painful; consider mixing with 1% lidocaine (without epinephrine) if permitted by protocol.
* Monitor for signs of hypermagnesemia, especially if renal function is impaired or high doses are administered.
* In eclampsia, magnesium sulfate is the treatment of choice and is more effective than anticonvulsants alone.
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*This information is intended for healthcare professionals. Always consult the most current prescribing information and institutional protocols for definitive guidance.*
