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# Magnesium Sulfate
## Overview
Magnesium sulfate is an essential mineral used to treat and prevent magnesium deficiency. It also has anticonvulsant properties and can be used in obstetrics.
## Primary Indications
* Hypomagnesemia
* Eclampsia and pre-eclampsia
* Torsades de Pointes
* Severe asthma exacerbations (adjunctive therapy)
## Adult Dosing
* **Hypomagnesemia:**
* Intramuscular (IM): 1-2 g (8-16 mEq) every 4-6 hours for 3-4 doses.
* Intravenous (IV): 4-6 g (32-48 mEq) infused over 4 hours, followed by a maintenance infusion of 1-2 g/hour (8-16 mEq/hour) as needed. Maximum maintenance dose generally 1-2 g/hour, but higher doses may be used cautiously under close monitoring.
* **Eclampsia/Pre-eclampsia:**
* Loading dose: 4-6 g (32-48 mEq) IV infused over 15-20 minutes.
* Maintenance dose: 1-2 g/hour (8-16 mEq/hour) IV infusion. Dosing may vary based on local protocols and patient response.
* **Torsades de Pointes:**
* 2-4 g (16-32 mEq) IV bolus, followed by an infusion of 1 g/hour (8 mEq/hour).
* **Severe Asthma Exacerbations:**
* 2 g (16 mEq) IV infused over 15-20 minutes.
## Pediatric Dosing
* **Hypomagnesemia:** Dosing is highly variable and depends on age, weight, and severity. Consult specialized pediatric resources or local protocols. Commonly cited ranges include:
* IM: 25-50 mg/kg/dose (0.1-0.2 mEq/kg/dose) every 4-6 hours. Maximum single dose generally 2 g.
* IV: 25-50 mg/kg/dose (0.1-0.2 mEq/kg/dose) infused over 10-30 minutes. Maintenance infusions vary widely, typically 0.1-0.5 mEq/kg/hour.
* **Eclampsia (Maternal):** Dosing generally follows adult recommendations. Pediatric use for eclampsia is rare and follows specific protocols.
* **Torsades de Pointes:** 25-50 mg/kg (0.1-0.2 mEq/kg) IV over 10-20 minutes.
## Dose Adjustments
Dose adjustments are generally not required in hepatic impairment. In renal impairment, doses should be reduced and serum magnesium levels closely monitored, especially in patients with severe renal dysfunction.
## Contraindications
* Hypermagnesemia
* Heart block
* Myocardial infarction (relative contraindication, use with caution)
* Hypersensitivity to magnesium sulfate
## Adverse Effects
* **Common:** Flushing, sweating, nausea, vomiting, hypotension, drowsiness, decreased deep tendon reflexes.
* **Serious:** Respiratory depression, cardiac arrest, loss of deep tendon reflexes, altered mental status, hypermagnesemia.
## Key Drug Interactions
* **Neuromuscular blocking agents:** Magnesium sulfate can potentiate neuromuscular blockade, increasing the risk of respiratory depression.
* **Calcium:** IV calcium may be used as an antidote for severe magnesium toxicity.
* **Tetracyclines and bisphosphonates:** Oral magnesium sulfate can decrease the absorption of these agents; administer them at least 2 hours before or 4-6 hours after magnesium.
## Monitoring
* **Serum magnesium levels:** Crucial, especially during IV infusions and in patients with renal impairment. Target levels vary by indication.
* **Renal function:** Monitor BUN and creatinine.
* **Vital signs:** Blood pressure, heart rate, respiratory rate.
* **Deep tendon reflexes:** Assess for loss of reflexes, indicating toxicity.
* **Urine output:** Ensure adequate renal excretion.
* **ECG:** Monitor for changes suggestive of cardiac effects.
## Clinical Pearls
* Magnesium sulfate is administered either as a vial containing a specific percentage (e.g., 50% solution = 500 mg/mL, equivalent to 4.06 mEq/mL) or as a premixed IV bag. Clarify the concentration carefully.
* Administer IV infusions slowly to avoid hypotension and respiratory depression. Rapid IV administration can be dangerous.
* A calcium gluconate IV bolus (e.g., 1 g) is the recommended antidote for symptomatic magnesium toxicity.
* In eclampsia, continuous IV infusion is preferred over intermittent IM doses due to more stable serum levels and better tolerability.
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**Disclaimer:** This information is intended for healthcare professionals and is not a substitute for professional medical advice. Always consult the most current prescribing information, institutional protocols, and patient-specific factors before making any treatment decisions.
