Perhaps a silly question, but I noticed that in FA 2016 is says to treat Crohn's with azathioprine, while for ulcerative colitis it lists 6-mercaptopurine. Isn't azathioprine just the prodrug for 6-MP, and thus there really shouldn't be a difference in using the two interchangeably in Crohn/UC? Maybe I'm missing something, any input would be great.