Low‐dose thioguanine guided by therapeutic drug monitoring is a safe and effective alternative in inflammatory bowel disease patients intolerant to conventional thiopurines

Background Thioguanine is an alternative thiopurine for inflammatory bowel disease (IBD) patients. Aims To evaluate the short‐term efficacy and safety of low‐dose therapeutic drug‐monitored (TDM) thioguanine. Methods A retrospective evaluation of IBD patients intolerant to conventional thiopurines started on thioguanine from 2017 to 2019 with dosing guided by TDM was conducted. Clinical response was defined for ulcerative colitis (UC) as a reduction of partial Mayo score ≥3 with reduction in rectal bleeding score of at least 1 and a final rectal bleeding subscore of 0–1 at Week 12 of therapy. Crohn disease (CD) response was defined as a reduction of Harvey‐Bradshaw index ≥3 (HBI) at Week 12 of therapy. Remission was defined in UC as partial Mayo score of