Interaction between mercaptopurine and milk.

Mercaptopurine is a purine analog used for acute lymphoblatic leukemia and chronic myelogenous leukemias. Since it is inactivated by xanthine oxidase (XO), concurrent intake of substances containing XO may potentially reduce bioavailability of mercaptopurine. Cow's milk is known to contain a high level of XO. In vitro and in vivo data suggest that concurrent intake of cow's milk may reduce the bioavailability of mercaptopurine. This interaction may be clinically significant. Therefore most patients should try to separate the timing of taking mercaptopurine and drinking milk.