2.2. Study Outcomes
The primary outcome of this study evaluated the percentage of time within therapeutic ANC range (defined as 500 – 1,500/μL) in the allopurinol cohort, with a comparison of values pre-initiation of allopurinol and post-initiation of allopurinol. ANC values were collected for all patients from the start of maintenance until the end of maintenance or May 31, 2022, whichever came first. Secondary endpoints included a comparison of the percentage of time within therapeutic ANC range between the allopurinol cohort and the standard treatment cohort, as well as the change in 6MMP:6TGN metabolite ratios within the allopurinol cohort compared to the standard treatment cohort. The resolution of hepatotoxicity, GI symptoms, rash, and hypoglycemia in the allopurinol cohort were also evaluated. All metabolite values obtained during maintenance therapy were collected for each patient. Patients in the allopurinol cohort with hepatotoxicity as a rationale for either metabolite collection or allopurinol initiation had AST, ALT, total bilirubin, and direct bilirubin values collected from the initiation of allopurinol, and for the 12 weeks following. Resolution of hepatotoxicity was defined as AST and ALT values less than 5x ULN and/or total bilirubin and direct bilirubin within normal limits at 12 weeks post allopurinol initiation. GI symptoms, rash, and hypoglycemia data were all obtained through provider progress notes. Resolution of GI symptoms, rash, and hypoglycemia were defined as subjective improvement based on provider notes at 12 weeks post allopurinol initiation. Descriptive dosing characteristics of allopurinol and 6MP post allopurinol initiation were collected.