Start with reduced starting doses (20%-50% of normal dose) if normal starting dose is ≥ 75 mg/m2/day or ≥ 1.5 mg/kg/day (e.g., start at 15-37.5 mg/m2/day or 0.3-0.75 mg/kg/day) and adjust doses of mercaptopurine based on degree of myelosuppression and disease-specific guidelines. At least 2-4 weeks will be required to reach steady-state after each dose adjustment. If myelosuppression occurs, and depending on other therapy, emphasis should be on reducing mercaptopurine over other agents (PMID 20354201,18685564, 8857546, 18987654, 20010622, 16401827, 11302950, 16530532, 9634537, 38230823). If normal starting dose is already < 37.5 mg/m2/day or < 0.75 mg/kg/day, dose reduction may not be recommended.