Magnesium Sulfate, Injection

1. Health Canada Product Monograph — Magnesium Sulfate, Injection

• First-line treatment for polymorphic ventricular tachycardia/torsades de pointes, regardless of the measured serum magnesium level, and for any ventricular arrhythmia associated with documented or suspected hypomagnesemia.
• Electrolyte replenishment in confirmed hypomagnesemia.
• Prevention and control of seizures in pre-eclampsia/eclampsia — a Health Canada–labelled indication for this product, unrelated to its arrhythmia use but relevant since the same product is stocked for both purposes.
• Not effective and not indicated for monomorphic ventricular tachycardia in a patient with a normal QT interval — its arrhythmia benefit is specific to the polymorphic/QT-prolongation setting.

• This is the standard agent used in pregnancy for eclampsia/severe pre-eclampsia seizure prophylaxis, and is also the correct first-line choice if torsades de pointes occurs during pregnancy.
• Use the shortest effective duration and monitor for signs of magnesium toxicity, since prolonged high-dose maternal use near delivery can cause neonatal respiratory or neuromuscular depression.

• Magnesium is a normal component of breast milk; a standard therapeutic course is considered compatible with breastfeeding.

• Health Canada has not authorized a specific geriatric indication. Use the lowest effective dose and monitor renal function, since impaired renal clearance increases the risk of magnesium accumulation and toxicity.

• Health Canada has not authorized a pediatric indication for this product. When magnesium is used for pediatric torsades de pointes, dosing (typically 25-50 mg/kg IV, maximum 2 g) should be directed by pediatric emergency or cardiology specialists.

• Torsades de pointes, pulseless (cardiac arrest): 1 to 2 g IV/IO push, diluted in 10 mL of 5% dextrose or 0.9% sodium chloride, given rapidly.
• Torsades de pointes or polymorphic VT with a pulse (hemodynamically tolerated): 1 to 2 g IV diluted in 50 to 100 mL of 5% dextrose or 0.9% sodium chloride, infused over 5 to 60 minutes depending on hemodynamic stability and urgency; follow with a continuous infusion of 0.5 to 1 g/hour if the arrhythmia is recurrent.
• Renal impairment: do not exceed 20 g in any 48-hour period; monitor serum magnesium closely and extend dosing intervals.
• Intramuscular route, non-arrhythmia indications, if IV access is unavailable: 1 to 5 g daily in divided doses for severe hypomagnesemia.
• Outside the rapid-push cardiac-arrest scenario, the IV infusion rate should not exceed 1.5 mL of 10% solution (or the equivalent) per minute, to avoid hypotension and flushing.

If overdose is suspected, seek emergency medical attention immediately or contact your regional Poison Control Centre without delay.

• Hypermagnesemia presents as loss of deep tendon reflexes (typically the first sign, around 4 mEq/L), muscle weakness, hypotension, sedation, and ECG changes; at higher levels (12-15 mEq/L), respiratory paralysis and complete heart block can occur.
• Treat by stopping the infusion, supporting ventilation, and giving IV calcium gluconate or calcium chloride to antagonize the cardiac and neuromuscular effects; hemodialysis may be required in severe renal-impairment-associated toxicity.

• Flushing, a sensation of warmth, mild hypotension, injection-site discomfort.

Serious side effects require immediate discussion with the prescriber or emergency care.

• Symptomatic hypotension, especially with rapid administration outside the cardiac-arrest bolus scenario.
• Respiratory depression, loss of deep tendon reflexes, complete heart block, and cardiac arrest at very high plasma levels.

• Renal impairment (the primary route of elimination — see renal dosing above).
• Myasthenia gravis — magnesium can worsen neuromuscular weakness.
• Concurrent use of other CNS or neuromuscular depressants.

• Known hypersensitivity.
• Heart block, unless being treated for torsades de pointes in a monitored setting with pacing available.
• Severe renal failure without careful dose adjustment and monitoring.

• Additive CNS/neuromuscular depression with other CNS depressants and with neuromuscular blocking agents.
• Additive hypotension with other vasodilators.
• Concurrent use with nifedipine or other calcium channel blockers can produce significant hypotension and neuromuscular blockade.
• Reduces the absorption of oral tetracyclines and fluoroquinolones if magnesium is also given enterally.

• Not applicable — parenteral formulation.

• Hospital or monitored setting; continuous ECG and blood pressure monitoring required, plus periodic deep-tendon-reflex and respiratory-rate checks when magnesium is used for higher-dose indications (eclampsia) or in renal impairment.

• Store at controlled room temperature.
• Single-use ampoule/vial — discard any unused portion; inspect for particulate matter or discolouration before use.

• This is a hospital-administered emergency and electrolyte-replacement medication.
• Patients treated for torsades de pointes should understand that the episode was linked to a QT-prolonging trigger (a drug, an electrolyte imbalance, or both) that needs to be identified and addressed before discharge to prevent recurrence.