Genetic polymorphisms of UGTs result in reduced enzyme activity and increased toxicity. UGT1A1*28 and UGT1A1*6 are reported to increase CPT-11-related toxicity in Asian patients. Moreover, the area under concentration curve (AUC) ratio of SN-38G to SN-38 is decreased in Asian patients having UGT1A1 *28 or UGT1A1*6. This implicated that the current standard dose of CPT-11 would be overdosing for homozygous UGT1A1*28/*28, *6/*6 or *28/*6 patients.