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# Magnesium Sulphate ## Overview Magnesium sulphate is an essential mineral that plays a crucial role in various physiological processes, including muscle and nerve function, blood glucose control, and blood pressure regulation. ## Primary Indications * **Eclampsia and Preeclampsia:** Prevention and treatment of seizures. * **Hypomagnesemia:** Treatment of low magnesium levels. * **Torsades de Pointes:** Treatment of polymorphic ventricular tachycardia. * **Bronchospasm:** Adjunctive therapy in severe acute asthma not responding to standard treatment. ## Adult Dosing * **Eclampsia Prophylaxis/Treatment:** Loading dose: 4-6 grams IV over 5-20 minutes, followed by a maintenance infusion of 1-2 grams/hour. Maximum maintenance dose generally 2 grams/hour, but can be increased to 4 grams/hour if indicated by clinical response and magnesium levels. * **Hypomagnesemia:** * **Severe (<0.5 mmol/L):** 4-6 grams IV infusion over 10-20 minutes, followed by 1 gram/hour infusion as needed. * **Less Severe (>0.5 mmol/L):** 1-2 grams IM or IV in divided doses over several hours. * **Torsades de Pointes:** 1-2 grams IV diluted in 10 mL of D5W, given as a bolus over 5-10 minutes. May repeat every 5-15 minutes. Followed by an infusion of 0.5-1 gram/hour. * **Bronchospasm:** 1-2 grams IV diluted in 50-100 mL NS or D5W over 15-20 minutes. *Note: Specific dosing can vary based on local protocols and institutional guidelines.* ## Pediatric Dosing * **Eclampsia:** Dosing is highly variable and often guided by specialist recommendations and weight-based calculations. A common regimen may involve a loading dose of 20-40 mg/kg (maximum 2 grams) IV followed by an infusion of 10-20 mg/kg/hour (maximum 1 gram/hour). * **Hypomagnesemia:** Dosing is typically weight-based and depends on the severity of deficiency. Reference to pediatric critical care guidelines is recommended. * **Torsades de Pointes:** 25-100 mg/kg IV (maximum 2 grams) over 10-20 minutes. *Note: Pediatric dosing requires careful calculation and close monitoring. Consult pediatric-specific guidelines.* ## Dose Adjustments * **Renal Impairment:** Magnesium sulphate is renally excreted. Dose reduction is necessary in patients with impaired kidney function to prevent accumulation and toxicity. Close monitoring of serum magnesium levels is crucial. In severe renal impairment, dosage may need to be significantly reduced or discontinued. ## Contraindications * Hypermagnesemia * Heart block * Myocardial infarction (relative contraindication in some cases, especially with bradycardia) * Hypersensitivity to magnesium sulphate ## Adverse Effects * **Common:** Flushing, sweating, nausea, vomiting, hypotension, decreased deep tendon reflexes. * **Serious:** Respiratory depression, cardiac arrhythmias, cardiac arrest, loss of deep tendon reflexes, somnolence, confusion, muscle weakness, hypothermia. ## Key Drug Interactions * **Neuromuscular Blocking Agents:** Magnesium sulphate can potentiate the effects of neuromuscular blockers, leading to prolonged neuromuscular blockade. * **Calcium Channel Blockers:** Additive hypotensive effects and potential for impaired cardiac contractility. * **Digoxin:** Increased risk of digoxin toxicity with hypermagnesemia. * **Tetracyclines and Quinolones:** Magnesium can decrease the absorption of these antibiotics; administer at least 2 hours apart or 4-6 hours after. ## Monitoring * **Serum Magnesium Levels:** Monitor frequently, especially during loading doses and maintenance infusions, to guide dosing and prevent toxicity. Target levels vary by indication (e.g., therapeutic range for eclampsia is typically 4-7 mEq/L or 2-3.5 mmol/L). * **Vital Signs:** Blood pressure, heart rate, respiratory rate. * **Deep Tendon Reflexes:** Assess for loss of reflexes, an early sign of toxicity. * **Urine Output:** Monitor for adequate renal function. * **Electrocardiogram (ECG):** Especially in Torsades de Pointes management and if cardiac concerns arise. ## Clinical Pearls * Magnesium sulphate should be administered cautiously in patients with renal impairment. * Monitor for signs of magnesium toxicity: decreased reflexes, decreased respiratory rate, altered mental status, hypotension. * Have calcium gluconate readily available as an antidote for severe magnesium toxicity. * IV administration of concentrated magnesium sulphate can cause pain and phlebitis; dilute appropriately. * For hypomagnesemia, oral magnesium supplements are generally preferred for chronic management once the patient is stable. **Disclaimer:** This information is intended for healthcare professionals. Always verify current prescribing information, institutional protocols, and patient-specific factors before administering any medication.