Magnesium Disorders

Mechanism

Hypomagnesemia

Defined as a plasma magnesium concentration less than 1.5 mEq/L (or < 1.8 mg/dL). It is classically associated with chronic alcoholism, poor intestinal absorption, prolonged use of proton pump inhibitors (omeprazole) and continuous treatment with loop diuretics or amphotericin B.

Indicators and dose

Rescue Indications for Magnesium Sulfate

The preferred treatment in clinical emergencies is based on the use of Magnesium Sulfate (in ampoules at 10%, 20% or 25% concentration):

• Torsades de Pointes (Torsades de Pointes) with Cardiac Instability: Administer a rapid intravenous bolus of 2 grams of Magnesium Sulfate (diluted in 10 mL of 5% dextrose) to be passed over a period of 1 to 2 minutes through a central peripheral line. A continuous maintenance infusion of 3 to 20 mg/minute can be continued according to electrocardiogram control.
• Eclampsia / Severe Pre-eclampsia in Obstetrics: Maternal neuroprotection protocol and seizure prevention. Administer loading doses of 4 to 6 grams of Magnesium Sulfate intravenously over a period of 20 minutes, followed by a continuous maintenance infusion of 1 to 2 grams per hour. The drug should be discontinued immediately if loss of patellar tendon reflexes, bradycardia, or decreased maternal respiratory rate is documented.

Hypermagnesemia

Defined as a serum magnesium concentration greater than 2.5 mEq/L (or < 3.0 mg/dL). It occurs almost exclusively in patients with advanced chronic kidney disease who consume antacids or laxatives rich in magnesium freely. Its excess acts by blocking the release of acetylcholine at the neuromuscular junction, manifesting clinically by abolition of reflexes, generalized flaccid weakness, respiratory paralysis and cardiac arrest.

The immediate emergency physiological antidote to severe magnesium toxicity is 10% Calcium Gluconate in a dose of 1 ampoule (10 mL) by direct intravenous route, which competitively antagonizes the neuromuscular effects.