Hypermagnesemia may occur when large dosage of Magnesium are given, especially in patients with renal failure.
Signs of hypermagnesemia include: nausea, vomiting, flushing, hypotension, muscle weakness, muscle paralysis, blurred or double vision, CNS depression and loss of reflexes. More severe hypermagnesemia may result in respiratory depression, respiratory paralysis, renal failure, coma, cardiac arrhythmias and cardiac arrest.
Treatment: The following measures may be required, blood pressure and respiratory support, i.v administration of 2.5 - 10 mmol calcium salt (i.e. Ca Gluconate) reverses the effects of magnesium toxicity, dialysis may be required, particularly if renal function is impaired. If renal function is normal, adequate fluid should be given so that urine output is at least 60 mL/hr to assist removal of magnesium from the body.
Antidotum of Magnesium Sulfate: 1 g Calcium Gluconate in 10 % injection i.v.