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# Magnesium Sulfate
## Overview
Magnesium sulfate is an essential mineral that plays a crucial role in numerous enzymatic reactions, neuromuscular transmission, and myocardial contraction. It is available in intravenous (IV) and intramuscular (IM) formulations.
## Primary Indications
* **Hypomagnesemia:** Treatment of low magnesium levels.
* **Preeclampsia/Eclampsia:** Prevention and treatment of seizures associated with preeclampsia and eclampsia.
* **Torsades de Pointes:** Treatment of polymorphic ventricular tachycardia associated with a prolonged QT interval.
* **Bronchospasm:** Adjunctive therapy for severe acute asthma or COPD exacerbations, particularly when unresponsive to standard treatment.
* **Constipation:** Oral magnesium citrate is used as a laxative.
## Adult Dosing
**Hypomagnesemia:**
* **Severe (serum Mg < 1.5 mEq/L or 0.75 mmol/L):**
* IV: 4-6 grams infused over 5-10 minutes, followed by 1-2 grams per hour continuous infusion. Dosing is adjusted based on serum magnesium levels and renal function. Maximum infusion rate typically 1-2 g/hour.
* IM: 4-5 grams (as 50% solution) divided into four doses and given deep IM every 4 hours until magnesium levels normalize.
* **Less Severe:** Dosing varies based on severity.
**Preeclampsia/Eclampsia:**
* **Loading Dose:** 4-6 grams IV infused over 5 minutes.
* **Maintenance Dose:** 1-2 grams per hour IV infusion.
* **IM alternative:** 5 grams of 50% solution IM in each buttock initially, followed by 5 grams IM every 4 hours.
**Torsades de Pointes:**
* IV: 1-2 grams diluted in 10-20 mL D5W, infused over 5-10 minutes. May repeat every 5-15 minutes. Continuous infusion of 0.5-1 gram per hour may follow if successful.
**Bronchospasm (Adjunctive):**
* IV: 1-2 grams diluted in 100 mL normal saline or D5W, infused over 15-30 minutes.
## Pediatric Dosing
Dosing is weight-based and severity-dependent and often guided by local protocol.
**Hypomagnesemia:**
* IV: 25-50 mg/kg per dose (max 2 grams) infused over 5-10 minutes. Followed by continuous infusion of 0.2-0.6 mEq/kg/hour (max 1 gram/hour).
**Eclampsia:**
* Loading Dose: 40 mg/kg IV (max 4 grams) infused over 5-10 minutes.
* Maintenance Dose: 10-15 mg/kg/hour IV infusion.
**Torsades de Pointes:**
* IV: 25-50 mg/kg (max 2 grams) infused over 10-20 minutes.
## Dose Adjustments
* **Renal Impairment:** Magnesium sulfate is renally excreted. Dose reduction is necessary in patients with impaired renal function. Monitor serum magnesium levels closely. Avoid in severe renal failure unless deficiency is confirmed and benefits outweigh risks.
## Contraindications
* Myocardial damage.
* Heart block.
* Hypermagnesemia.
* Hyperkalemia (use with caution).
* Hypocalcemia (use with caution, as magnesium can worsen hypocalcemia).
* Anuria.
## Adverse Effects
Common: Flushing, hypotension, somnolence, decreased deep tendon reflexes, nausea, vomiting.
Serious: Respiratory depression, cardiac arrest, hypermagnesemia (especially with renal impairment), hypocalcemia, loss of deep tendon reflexes, muscle weakness, diaphoresis.
## Key Drug Interactions
* **Neuromuscular Blocking Agents:** Potentiates neuromuscular blockade, increasing the risk of prolonged paralysis and respiratory depression.
* **Calcium Channel Blockers:** Increased risk of hypotension and neuromuscular blockade.
* **Digitalis:** Risk of cardiac arrhythmias, especially with IV calcium administration.
* **Tetracyclines and Quinolones:** Magnesium sulfate may decrease the absorption of oral tetracyclines and fluoroquinolone antibiotics; administer at least 2 hours before or 4-6 hours after magnesium.
## Monitoring
* **Serum Magnesium Levels:** Essential for guiding dosing and assessing efficacy.
* **Renal Function:** Monitor creatinine and BUN, especially in patients with risk factors for renal impairment.
* **Deep Tendon Reflexes:** Assess for loss of reflexes, which can indicate hypermagnesemia.
* **Respiratory Rate and Effort:** Monitor for signs of respiratory depression.
* **Blood Pressure:** Magnesium can cause hypotension.
* **Urine Output:** Adequate urine output is crucial for magnesium excretion.
* **ECG:** Especially when used for Torsades de Pointes or in patients with cardiac conditions.
## Clinical Pearls
* Always dilute magnesium sulfate for IV infusion to avoid rapid administration, which can cause hypotension and cardiac arrhythmias.
* Monitor for signs of hypermagnesemia, particularly in patients with renal impairment. Symptoms include decreased deep tendon reflexes, somnolence, respiratory depression, and cardiac arrest.
* IV calcium may be used as an antidote for severe magnesium toxicity.
* In pregnant patients receiving magnesium sulfate for preeclampsia, monitor fetal heart rate closely.
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*Disclaimer: This information is intended for healthcare professionals. Always consult the most current prescribing information and institutional protocols for definitive dosing and safety guidelines. This content does not substitute for professional medical advice.*
