Enhanced absorption with citrates or ascorbic acid. Decreases absorption of allopurinol, tetracyclines, quinolones, cephalosporins, biphosphonate derivatives, corticosteroids, cyclosporin, delavirdine, Fe salts, imidazole antifungals, isoniazid, mycophenolate, penicillamine, phosphate supplements, phenytoin, phenothiazines, trientine.