Hypermagnesaemia

The normal range of the adult serum or plasma magnesium concentration is 0.8 to 1.0 mmol/L.¹

Common causes of hypermagnesaemia lists the common causes of hypermagnesaemia (a serum magnesium concentration above 1.0 mmol/L). Moderate to severe and symptomatic hypermagnesaemia is usually due to excessive intake of magnesium (eg antacids, enemas, intravenous infusion), most often with concomitant kidney impairment. The most common clinical features of moderate to severe hypermagnesaemia are neuromuscular (eg loss of deep tendon reflexes, muscle paralysis, impaired consciousness, respiratory depression). Other features can include anorexia, nausea, skin flushing, hypotension, bradycardia/heart block and cardiac arrest. Hypermagnesaemia often induces hypocalcaemia.

The potential for developing hypermagnesaemia should be considered in patients receiving magnesium therapy, especially if their kidney function is impaired. If hypermagnesaemia develops, magnesium therapy should stop. In severe magnesium intoxication (serum magnesium concentration higher than 2.0 to 2.5 mmol/L), an intravenous calcium infusion provides immediate but transient antagonism of the toxic effects. Kidney excretion should be promoted with intravenous sodium chloride 0.9%, aiming for a urine output of at least 60 mL per hour. If this urine output can't be achieved, intravenous furosemide (frusemide) can be added. Dialysis may be needed in patients with kidney impairment.