Irinotecan (7-ethyl-10- {4(-1-piperidino)-1-piperidino} carbonyloxy camptothecin) is a semisynthetic camptothecin derivative introduced in the 1980's. Irinotecan is a prodrug metabolized by carboxylesterases to an active metabolite 7-ethyl-10-hydroxy-camptothecin (SN38). SN38 exerts its cytotoxic effect by forming stable complexes with topoisomerase I and DNA. These complexes collide with replication forks and cause breaks in DNA. Studies substantiated irinotecan's activity in 5FU resistant colorectal cancer and led to its approval for treatment of 5FU resistant colorectal cancer in the United States, Canada and Europe.Colorectal cancer studies demonstrated that single agent irinotecan's dose limiting toxicity was diarrhea occurring 5 to 6 days after its administration. High dose loperamide at first occurrence of diarrhea has decreased the incidence of diarrhea but the incidence of grade 3/4 diarrhea remains high at 28 to 40%.