Hypercalcaemia and possibly metabolic alkalosis can develop in patients given large amounts of calcium (with or without high doses of vitamin D) if they are also given
thiazide diuretics, which can reduce the urinary excretion of calcium.
This interaction is unlikely to be of importance in patients taking occasional calcium e.g. in
antacids. Consider monitoring calcium levels in those given a thiazide and a calcium supplement or large amounts of calcium
antacids regularly.