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Hypermagneaemia is predominantly the result of renal failure. Occasionally, it occurs when magnesium salts are given rectally in patients with colonic disease or in association with hypothyroidism, lithium therapy and the milk alkali syndrome.

Symptoms of hypermagnesaemia are usually apparent at levels above 2 mmol/l. Features include:

  • muscle weakness - with possibly, a flaccid paralysis
  • confusion and mental obtundation
  • respiratory paralysis
  • cardiac arrest - in extreme cases

The ECG may show increased PR interval, broadened QRS complex or elevated T waves.

Treatment is directed at the underlying cause.

Calcium chloride may be given intravenously as it is antagonistic to magnesium; 500 mg or more at a rate of 100 mg/min is typical.

Haemodialysis or peritoneal dialysis may be indicated in acute renal failure.