Considering these findings, a likely interaction between 5-ASA and TPMT/6-TGN needs to be considered seriously, as patients with IBD, especially with active ulcerative colitis (UC), may be receiving high doses of 5-ASA, up to 4 g/day, and, with such a high dose, the inhibition of TPMT and increase in the mean 6-TGN levels cannot be disregarded, even with dose-adjusting thiopurines [12,29,38]. This evidence concerns the gene TPMT and inflammatory bowel disease.