Magnesium Sulphate

# Magnesium Sulphate ## Overview - **Classification**: Electrolyte, Anticonvulsant, Tocolytic, Antiarrhythmic - **Mechanism**: Blocks neuromuscular transmission, depresses CNS, causes vasodilation, antagonizes calcium channels. ## Primary Indications 1. **Hypomagnesemia** - Treatment and prevention of low magnesium levels. 2. **Eclampsia/Pre-eclampsia** - Prevention and treatment of seizures. 3. **Torsades de Pointes** - Treatment of polymorphic ventricular tachycardia. 4. **Asthma Exacerbation** - Acute severe asthma unresponsive to standard therapy. ## Adult Dosing ### Standard Dosing **Hypomagnesemia (Mild-Moderate)** - **Dose**: **1-4 grams** - **Frequency**: Every 4-6 hours - **Route**: IV infusion over 1-2 hours or IM (painful) - **Duration**: Until magnesium levels normalize **Hypomagnesemia (Severe)** - **Dose**: **4-8 grams** - **Frequency**: Initial bolus followed by continuous infusion - **Route**: IV infusion slowly over 2-4 hours, then **3-4 grams/hour** by infusion for up to 24 hours - **Maximum**: Infusion rate should not exceed **1 mg/kg/minute** **Eclampsia/Severe Pre-eclampsia (Loading Dose)** - **Dose**: **4-6 grams** - **Frequency**: Once - **Route**: IV infusion over 15-20 minutes **Eclampsia/Severe Pre-eclampsia (Maintenance Dose)** - **Dose**: **1-2 grams** - **Frequency**: Hourly - **Route**: IV continuous infusion for 24 hours post-delivery or last seizure - **Maximum**: Infusion should not exceed **3 grams/hour** **Torsades de Pointes** - **Dose**: **1-2 grams** - **Frequency**: Once - **Route**: IV bolus over 5-20 minutes - **Considerations**: Repeat if Torsades recurs **Acute Severe Asthma Exacerbation** - **Dose**: **1.2-2 grams** - **Frequency**: Once - **Route**: IV infusion over 15-30 minutes ### Dose Adjustments - **Renal Impairment**: Reduce dose by 25-50% for CrCl <30 mL/min. - **Renal Impairment**: Monitor serum magnesium and renal function closely. - **Hepatic Impairment**: No specific dose adjustment needed. - **Elderly Patients**: Start at lower end of dosing range due to potential for decreased renal function. ## Pediatric Dosing ### Neonates (0-28 days) **Hypomagnesemia** - **Dose**: **25-50 mg/kg** (**0.2-0.4 mEq/kg**) - **Frequency**: Every 8-12 hours - **Route**: IV infusion over 2-3 hours - **Maximum**: **400 mg/kg/day** OR **1 gram/day** ### Infants (1-12 months) **Hypomagnesemia** - **Dose**: **25-50 mg/kg** (**0.2-0.4 mEq/kg**) - **Frequency**: Every 8-12 hours - **Route**: IV infusion over 2-3 hours - **Maximum**: **1000 mg** per dose ### Children (1-12 years) **Hypomagnesemia** - **Dose**: **25-50 mg/kg** (**0.2-0.4 mEq/kg**) - **Frequency**: Every 6-12 hours - **Route**: IV infusion over 2-3 hours - **Maximum**: **2 grams** per dose **Acute Severe Asthma Exacerbation** - **Dose**: **25-50 mg/kg** - **Frequency**: Once - **Route**: IV infusion over 15-20 minutes - **Maximum**: **2 grams** ### Adolescents (13-18 years) - **Dose**: Generally follow adult dosing recommendations. - **Maximum**: Adult maximum doses apply. ## Safety Information ### Contraindications - **Absolute**: Myocardial damage/heart block (especially with IV administration) - **Absolute**: Severe renal impairment (anuria) - **Absolute**: Hypersensitivity to magnesium sulfate - **Relative**: Acute abdomen (intestinal obstruction) ### Common Adverse Effects - **Very Common (>10%)**: Flushing, sweating, warm sensation - **Common (1-10%)**: Hypotension, headache, nausea, vomiting, muscle weakness - **Serious but Rare**: Respiratory depression, cardiac arrest, CNS depression, magnesium toxicity ### Key Drug Interactions - **Neuromuscular Blockers**: Potentiates effects, prolonged paralysis. - **CNS Depressants**: Additive CNS depression (sedation, respiratory depression). - **Calcium Channel Blockers**: Increased risk of hypocalcemia and hypotension. - **Digoxin**: Bradycardia, AV block (use with caution). ## Monitoring & Follow-up - **Before Treatment**: Baseline serum magnesium, renal function (CrCl), deep tendon reflexes (DTRs), vital signs. - **During Treatment**: Serum magnesium levels (e.g., every 6-12h or as clinically indicated), vital signs, DTRs, urine output. - **During Treatment (Eclampsia)**: Continuous fetal heart rate monitoring. - **Clinical Signs**: Monitor for loss of DTRs, respiratory rate <12 bpm, urine output <30 mL/hour (signs of toxicity). ## Clinical Pearls - 💡 **Antidote**: Calcium gluconate 10% 10 mL IV over 5-10 minutes is the antidote for magnesium toxicity. - 💡 **Infusion Rate**: Administer IV infusions slowly to minimize adverse effects like flushing and hypotension. - 💡 **Pre-eclampsia**: Magnesium solely prevents seizures, does not lower blood pressure. - 💡 **DTRs**: Loss of deep tendon reflexes is an early sign of magnesium toxicity. > **⚠️ Important**: This information is for educational purposes only. Always consult current prescribing information, local guidelines, and clinical judgment before prescribing.