Magnesium Sulfate

# Magnesium sulfate ## Overview - **Classification**: Electrolyte, Anticonvulsant, Tocolytic, Antiarrhythmic. - **Mechanism**: Physiological calcium antagonist; CNS depressant, reduces acetylcholine release at neuromuscular junction; relaxes smooth muscle. ## Primary Indications 1. **Eclampsia/Pre-eclampsia**: Seizure prophylaxis and treatment. 2. **Torsades de Pointes (TdP)**: Treatment of polymorphic ventricular tachycardia. 3. **Severe Asthma Exacerbation**: Adjunctive therapy for acute severe asthma. 4. **Hypomagnesemia**: Treatment of severe, symptomatic magnesium deficiency. ## Adult Dosing ### Standard Dosing **Eclampsia/Pre-eclampsia (Seizure Prophylaxis/Treatment)** - **Dose**: **4-6 g IV** loading dose over 15-20 minutes. - **Frequency**: Followed by **1-2 g/hour IV** continuous infusion. - **Route**: Intravenous (IV). - **Duration**: Typically 24 hours post-delivery or last seizure. **Torsades de Pointes (TdP)** - **Dose**: **1-2 g IV** over 5-20 minutes. For pulseless TdP, administer over 1-2 minutes. - **Frequency**: May repeat once if needed; then consider infusion. - **Route**: Intravenous (IV). **Severe Asthma Exacerbation** - **Dose**: **1.2-2 g IV** over 15-30 minutes. - **Frequency**: Single dose. - **Route**: Intravenous (IV). **Hypomagnesemia (Severe, Symptomatic)** - **Dose**: **1-2 g IV** over 5-60 minutes initially. - **Frequency**: Followed by **3-6 g IV** over 24 hours, often given as 1-2 g every 4-6 hours. - **Route**: Intravenous (IV). - **Special Considerations**: Adjust dose based on serum magnesium levels. ### Dose Adjustments - **Renal Impairment**: Use with caution. **Contraindicated if CrCl <30 mL/min**. Reduce dose by 50% or more. Closely monitor serum Mg levels, DTRs, and urine output. - **Hepatic Impairment**: No specific adjustment required; monitor renal function if comorbidities exist. - **Elderly Patients**: Start at lower end of dosing range due to potential decreased renal function and increased sensitivity. ## Pediatric Dosing ### Neonates (0-28 days) - **Indication**: Hypomagnesemia. - **Dose**: **25-50 mg/kg IV** over 2-3 hours. - **Frequency**: Every 8-12 hours as needed. - **Maximum**: **400 mg/kg/day**. - **Special Notes**: Infuse slowly to prevent hypotension. Monitor respiratory rate and muscle tone. ### Infants (1-12 months) - **Indication**: Severe Asthma Exacerbation. - **Dose**: **25-50 mg/kg IV** over 10-20 minutes. - **Maximum**: **2 g/dose**. - **Indication**: Hypomagnesemia. - **Dose**: **25-50 mg/kg IV** over 2-3 hours. - **Frequency**: Every 8-12 hours as needed. - **Maximum**: **400 mg/kg/day**. ### Children (1-12 years) - **Indication**: Severe Asthma Exacerbation. - **Dose**: **25-50 mg/kg IV** over 10-20 minutes. - **Maximum**: **2 g/dose**. - **Indication**: Hypomagnesemia. - **Dose**: **25-50 mg/kg IV** over 2-3 hours. - **Frequency**: Every 8-12 hours as needed. - **Maximum**: **400 mg/kg/day**. ### Adolescents (13-18 years) - **Dose**: Generally follow adult dosing recommendations. - **Maximum**: Adult maximum doses. ## Safety Information ### Contraindications - **Absolute**: Myocardial damage, heart block (any degree). - **Absolute**: Severe renal failure (CrCl <30 mL/min). - **Absolute**: Hypersensitivity to magnesium sulfate. - **Relative**: Myasthenia gravis (may exacerbate muscle weakness). ### Common Adverse Effects - **Very Common (>10%)**: Flushing, sweating, warmth sensation, hypotension. - **Common (1-10%)**: Nausea, vomiting, headache, dizziness, blurred vision, hyporeflexia. - **Serious but Rare**: Respiratory depression, cardiac arrest, profound CNS depression, pulmonary edema, circulatory collapse. ### Key Drug Interactions - **CNS Depressants (e.g., opioids, benzodiazepines)**: Potentiates sedative effects. Monitor for increased sedation and respiratory depression. - **Calcium Channel Blockers (e.g., nifedipine, verapamil)**: Increased risk of hypotension and bradycardia. Monitor blood pressure and heart rate closely. - **Neuromuscular Blockers**: Potentiates and prolongs neuromuscular blockade. Monitor respiratory function and need for mechanical ventilation. - **Digoxin**: Increased risk of AV block. Monitor ECG. ## Monitoring & Follow-up - **Before Treatment**: Baseline serum magnesium, calcium, potassium, renal function (Cr, BUN), blood pressure, heart rate, deep tendon reflexes (DTRs). - **During Treatment**: Hourly vital signs (BP, HR, RR), DTRs (patellar reflex), urine output. Monitor serum Mg levels every 4-6 hours (eclampsia) or as clinically indicated (hypomagnesemia). - **Clinical Signs**: Watch for loss of DTRs, decreased respiratory rate (<12 breaths/min), lethargy, decreased urine output (<25 mL/hour), and cardiac arrhythmias. ## Clinical Pearls - 💡 **Antidote Availability**: Keep **calcium gluconate 1 g IV** readily available. Administer over 3-5 minutes for magnesium toxicity (e.g., respiratory depression, absent DTRs). - 💡 **Infusion Rate**: Always infuse magnesium slowly. Rapid IV bolus can cause sudden hypotension, flushing, and cardiac arrest. - 💡 **Renal Function**: Magnesium is 100% renally cleared. Impaired renal function is the most common cause of toxicity. - 💡 **Formulation Check**: Verify correct concentration (e.g., 20% vs 50%) and dilute appropriately before administration to prevent errors. > **⚠️ Important**: This information is for educational purposes only. Always consult current prescribing information, local guidelines, and clinical judgment before prescribing.