Cell cycle-specific (S phase) purine antagonist antimetabolite that inhibits RNA and DNA synthesis.

Acute lymphocytic leukemia, acute myelocytic leukemia, acute myelomonocytic leukemia.

Metabolized in the liver; excreted in urine.

Initial dose 2.5 mg/kg per day PO as a single dose. When in hematologic remission, start maintenance dose at 1.5 to 2.5 mg/kg per day as a single dose. If patient is to receive concurrent allopurinol, reduce 6-mercaptopurine dose to one-third or one-fourth usual dose.