Enhanced effects of digitalis glycosides on the heart & may precipitate digitalis intoxication. Hypercalcemia w/ thiazide diuretics or vit D. May predispose to milk-alkali syndrome w/ thiazide diuretics. Reduced absorption of bisphosphonates (eg, alendronate), fluoride, some fluoroquinolones & tetracyclines, levothyroxine, phenytoin, & minerals (eg, Fe & Zn). Decreased effectiveness of aspirin, bismuth subcitrate, Ca channel blocker, & cefpodoxime. Decreased bioavailability of atenolol. Reduced absorption w/ alcohol, Al-containing antacids, mineral oil, stimulant laxatives (prolonged use), & corticosteroids. May reduce serum levels w/ anticonvulsants.