<p><strong>Calcium</strong>: Co-administration with thiazide diuretics or vit D may lead to milk-alkali syndrome and hypercalcaemia. Decreased absorption with corticosteroids. Decreases absorption of tetracyclines, atenolol, iron, quinolones, alendronate, Na fluoride, Zn and calcium-channel blockers. Enhances cardiac effects of digitalis glycosides and may precipitate digitalis intoxication.<br />
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<strong>Calcitriol</strong>: Hypermagnesaemia may develop in patients on chronic renal dialysis. Hypercalcaemia in patients on digitalis may precipitate cardiac arrhythmias. Intestinal absorption of calcitriol may be reduced by cholestyramine and colestipol. Phenytoin, barbiturates may decrease the T1/2 of calcitriol. May develop hypercalcaemia with thiazide diuretics.</p>