For adults and children the usual dose is 2.5 mg/kg bodyweight per day, but the dose and duration of administration depend on the nature and dosage of other cytotoxic agents given in conjunction with Mercaptopurine. The dosage should be carefully adjusted to suit the individual patient. Mercaptopurine has been used in various combination therapy schedules for acute leukemia and the literature should be consulted for details. Consideration should be given in reducing the dosage in patients with impaired hepatic or renal function. When allopurinol and mercaptopurine are administered concomitantly it is essential that only a quarter of the usual dose of mercaptopurine is given since allopurinol decreases the rate of catabolism of mercaptopurine. Maintenance schedules, the dose may vary from 1.5 to 2.5 mg/kg per day as a single dose. Or as prescribed by the physician.