Initiate therapy with decreased starting doses (20-50% of standard starting dose) if starting dose is ≥75 mg/m2/day (for malignancy) or ≥1.5 mg/kg/day (for nonmalignancy). If starting dose is already below standard starting dose, dose reduction might not be necessary. During therapy, adjust mercaptopurine doses based on the degree of myelosuppression and disease-specific guidelines. It usually takes at least 2-4 weeks of stable dosing to reach steady state after each dose adjustment. If myelosuppression occurs, and the patient is on combination therapy, emphasis should be on reducing mercaptopurine over other agents.