<p>Oral Calcium can reduce the absorption of tetracycline &amp; fluoride preparations and minimum 3 hours time should be allowed between ingestion of these medications. Thiazide diuretics reduces the renal excretion of Calcium. Phenytoin, barbiturates, glucocorticoids may induce metabolism of Vitamin D3. Concomitant ingestion of certain foods like spinach, cereals, milk and its derivatives may reduce the intestinal uptake of Calcium.</p>