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# Magnesium Sulfate
## Overview
Magnesium sulfate is an electrolyte that plays a role in numerous biochemical reactions. It is available for intravenous (IV) and intramuscular (IM) administration.
## Primary Indications
* Treatment of hypomagnesemia.
* Prevention and treatment of seizures in preeclampsia and eclampsia.
* Management of torsades de pointes.
* Adjunct in the management of status asthmaticus.
## Adult Dosing
* **Hypomagnesemia:**
* **Severe:** 4-6 grams IV initially, followed by 2-4 grams IV every 4-12 hours.
* **Less severe:** Dosing varies based on serum magnesium levels and patient response; consult institutional protocol or specific guidelines.
* **IM administration:** Typically 1-2 grams IM every 4-6 hours for 4 doses.
* **Preeclampsia/Eclampsia:**
* **Loading dose:** 4-6 grams IV infusion over 5-20 minutes.
* **Maintenance dose:** 1-2 grams per hour IV infusion. Dosing may be adjusted based on seizure recurrence or toxicity.
* **Torsades de Pointes:**
* 1-2 grams IV in 10 mL D5W over 5-10 minutes, followed by continuous infusion of 0.5-1 gram per hour.
* **Status Asthmaticus:**
* 2 grams IV infusion in 50-100 mL normal saline over 15-30 minutes.
## Pediatric Dosing
* **Hypomagnesemia:** Dosing is weight-based and varies significantly with severity. Consult pediatric-specific guidelines or institutional protocols.
* A common initial IV dose is 25-50 mg/kg/dose (maximum 2 grams) infused over 10-15 minutes.
* Maintenance infusions are typically 10-30 mg/kg/day (maximum 1 gram/day).
* **Status Asthmaticus:**
* Typically 25-40 mg/kg IV infusion over 15-30 minutes (maximum 2 grams).
## Dose Adjustments
* **Renal Impairment:** Magnesium is renally excreted. Dose reduction and careful monitoring are necessary in patients with impaired renal function.
## Contraindications
* Hypermagnesemia.
* Heart block or myocardial damage (in patients receiving IV magnesium).
## Adverse Effects
* **Common:** Flushing, warmth, hypotension, nausea, vomiting, drowsiness, decreased reflexes.
* **Serious:** Respiratory depression, cardiac arrhythmias, cardiac arrest, hypermagnesemia (especially in renal impairment).
## Key Drug Interactions
* **Neuromuscular Blocking Agents:** Magnesium can potentiate neuromuscular blockade, leading to prolonged muscle weakness or paralysis.
* **Calcium Salts:** May antagonize the cardiac effects of magnesium toxicity.
* **Tetracyclines and Fluoroquinolones:** Oral magnesium can decrease the absorption of these antibiotics; administer at least 2 hours apart.
## Monitoring
* **Serum Magnesium Levels:** Monitor closely, especially during rapid infusion or in patients with renal impairment. Therapeutic levels for hypomagnesemia are typically 1.7-2.2 mmol/L (4-5.5 mg/dL). For eclampsia, levels between 4-7 mmol/L (9.6-16.8 mg/dL) are generally targeted, but toxicity can occur at lower levels.
* **Renal Function:** Assess baseline and periodically.
* **Deep Tendon Reflexes:** Diminished reflexes are an early sign of toxicity.
* **Respiratory Rate:** Monitor for signs of respiratory depression.
* **Urine Output:** Maintain adequate urine output.
* **ECG:** Consider in patients receiving high doses or experiencing toxicity.
## Clinical Pearls
* Magnesium sulfate is a smooth muscle relaxant and vasodilator.
* Always dilute magnesium sulfate for IV infusion to prevent rapid administration, which can cause hypotension and cardiac arrest.
* The antidote for magnesium toxicity is IV calcium (e.g., calcium gluconate).
* Intramuscular administration can be painful; consider co-administration with lidocaine (check local protocols).
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**Disclaimer:** This information is intended for clinical decision support and does not replace the need to consult the official prescribing information and relevant clinical guidelines for the most current and complete drug information. Always verify current drug information with the manufacturer's package insert or other authoritative sources.
