The risk of hypercalcaemia should be considered in patients taking thiazide diuretics since these drugs can reduce urinary calcium excretion. Hypercalcaemia must be avoided in digitalised patients.
The effects of digitalis and other cardiac glycosides may be accentuated with the oral administration of calcium combined with Vitamin D. Strict medical supervision is needed and, if necessary monitoring of ECG and calcium.
Certain foods (e.g. those containing oxalic acid, phosphate or phytinic acid) may reduce the absorption of calcium
Calcium salts may reduce the absorption of thyroxine, bisphosphonates, sodium fluoride, quinolone and tetracycline antibiotics or iron. It is advisable to allow a minimum period of four hours before taking the calcium.
Calcium absorption is reduced in patients receiving systemic corticosteroid therapy. This should be taken in to account when patients are receiving concomitant therapy.