Symptoms
Overdose can lead to hypervitaminosis, hypercalciuria and hypercalcaemia. Symptoms of hypercalcaemia may include anorexia, dehydration, thirst, nausea, vomiting, constipation, abdominal pain, muscle weakness, fatigue, mental disturbances, polydipsia, polyuria, bone pain, nephrocalcinosis, renal calculi and in severe cases, cardiac arrhythmias. Extreme hypercalcaemia may result in coma and death.
Persistently high calcium levels may lead to irreversible renal damage, soft tissue calcification, vascular and organ calcification.
The milk-alkali syndrome of hypercalcaemia, alkalosis and renal impairment still occur in patients who ingest large amounts of calcium and absorbable alkali; it is not uncommon as a cause of hypercalcaemia requiring hospitalisation. The syndrome has also been reported in a patient taking recommended doses of antacids containing calcium carbonate for chronic epigastric discomfort, and in a pregnant woman taking high, but not grossly excessive, doses of calcium (about 3 g of elemental calcium daily). Metastatic calcification can develop.
The threshold for vitamin D intoxication is between 40,000 and 100,000 IU per day and for calcium intoxication is from supplementation in excess of 2000 mg per day, taken for several months, in persons with normal parathyroid function.
Management
Treatment is essentially symptomatic and supportive.
Treatment of hypercalcaemia: The treatment with calcium and vitamin D must be discontinued. Treatment with thiazide diuretics, lithium, vitamin A, vitamin D and cardiac glycosides must also be discontinued (see section 4.5).
Rehydration, and, according to severity, isolated or combined treatment with loop diuretics (e.g. furosemide), bisphosphonates, calcitonin and corticosteroids should be considered. In patients with renal failure, hydration is ineffective and they should undergo dialysis. Serum electrolytes, renal function and diuresis must be monitored. In severe cases, ECG and CVP should be followed.
In the case of persistent hypercalcaemia, contributing factors should be excluded, e.g. primary hyperparathyroidism, malignancies, renal failure or immobilisation.
Depending on the degree of hypercalcaemia and on the patient's condition, e.g. in case of oligoanuria, haemodialysis (calcium-free dialysate) may be necessary.