29. Magnesium sulphate ( MgSO4 )
Uses:
🔹 Eclampsia and Preeclampsia: First-line therapy for seizures in preeclampsia and eclampsia.
🔹 Torsades de Pointes, a life-threatening ventricular arrhythmia.
🔹 Asthma Exacerbation: adjunct therapy in severe asthma exacerbations unresponsive to standard treatment.
🔹 Hypomagnesemia
🔹 Constipation: Used as a laxative for acute constipation.
🔹 Neuroprotection in Preterm Labor: Used to reduce the risk of cerebral palsy in preterm labor when administered before delivery.
🔹 Tocolysis (Controversial use)
Dose:
🔹 Eclampsia and Preeclampsia:
• IV Loading Dose: 4-6 g IV over 20 minutes.
• IV Maintenance: 1-2 g/hour continuous infusion for 24 hours.
• IM Dose: Loading dose of 5g IM on each buttock, f/b 4-5 g IM every 4 hours (alternating buttocks), given as a deep IM injection.
🔹 Torsades de Pointes (Adults):
• Dose: 1-2 g IV over 5-15 minutes.
🔹 Severe Asthma Exacerbation (Adults):
• Dose: 1.2-2 g IV over 20 minutes.
🔹 Hypomagnesemia (Adults):
• Mild Deficiency: 1-2 g IV over 1 hour.
• Severe Deficiency: 2-4 g IV over 2-4 hours.
🔹 Neuroprotection in Preterm Labor:
• Loading Dose: 4-6 g IV over 20-30 minutes, followed by 1-2 g/hour infusion for up to 24 hours.
🔹 Pediatrics:
• Dose: 25-50 mg/kg IV over 20 minutes (maximum dose 2 g).
Presentation:
🔹 Injection: 50% (500 mg/mL) & 25% (250 mg/ml) solution in 10 mL, 20 mL, or 50 mL vials or ampules.
🔹 Oral Solution: 500 mg/5 mL oral solution
Note:
🔹 Mechanism of Action: MgSO4 increases intracellular magnesium levels, stabilizing cellular membranes, inhibiting calcium entry into cells, and reducing excitability in neurons and cardiac myocytes. It also reduces smooth muscle contraction and has a bronchodilatory effect.
🔹 Pharmacokinetics:
• Onset: IV onset within 30 minutes; rapid with immediate cardiovascular effects.
• Duration: Variable depending on dose and indication; approximately 30 minutes to 1 hour for arrhythmia treatment.
🔹 Side Effects:
• Common: Flushing, hypotension, sweating, nausea, vomiting.
• Serious: Respiratory depression, hyporeflexia, cardiac arrhythmias, and hypermagnesemia.
🔹 Contraindications:
• Heart block or myocardial damage.
• Severe renal impairment (risk of magnesium toxicity).
🔹 Special Considerations:
• Route-specific Considerations:
• IV administration should be slow and diluted to avoid toxicity.
• IM injections can cause pain and local irritation.
• Electrolyte Imbalances: Magnesium sulfate can affect other electrolytes, particularly calcium and potassium.
• Toxicity: Early signs include loss of deep tendon reflexes (hyporeflexia). Monitor magnesium levels and clinical signs.
• Magnesium Toxicity Management: Calcium gluconate or calcium chloride can be administered as an antidote for toxicity.
• Alternative Magnesium Preparations: Other magnesium salts (e.g., magnesium chloride, magnesium oxide) may be preferred in certain situations, depending on the clinical scenario.
🔹 Drug Interactions:
• Calcium Channel Blockers: Concurrent use may increase the risk of severe hypotension and respiratory depression.
• CNS Depressants: Increased risk of respiratory depression when combined with other CNS depressants like opioids or sedatives.
• Neuromuscular Blockers: Magnesium can potentiate the effects of neuromuscular blocking agents, requiring close monitoring.
🔹 Monitoring:
• Continuous ECG and vital sign monitoring during IV infusion for cardiac indications.
• Regular monitoring of serum magnesium levels and electrolytes, particularly during prolonged therapy.
• Monitor deep tendon reflexes to assess for early signs of magnesium toxicity.
References:
🔹 NCBI StatPearls - Magnesium Sulfate: https://www.ncbi.nlm.nih.gov/books/NBK554553/
🔹 Goodman & Gilman’s The Pharmacological Basis of Therapeutics, 13th edition
🔹 American College of Obstetricians and Gynecologists. Magnesium sulfate use in obstetrics. Committee Opinion No. 652. Obstet Gynecol 2016;127:e52–3.
🔹 World Health Organization. WHO Recommendation: Magnesium Sulfate for the Prevention of Eclampsia. Geneva: WHO; 2011.