Conclusions
  1. The incidence of aberrant metabolism of mercaptopurine in our study was above 50% and is likely more prevalent in the ALL and LL populations than previously reported
  2. Utilizing our proposed algorithm for introduction the of allopurinol to mitigate mercaptopurine metabolite toxicity is both a safe and effective intervention, but does require close interval monitoring
  3. Identification of a therapeutic 6-MMPN:6-TGN ratio may be helpful in guiding decisions to start hybrid allopurinol-mercaptopurine therapy as well as guide dose titration.