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