UGT1A1 and Decreased total neutrophil count: Indeed, they showed that patients receiving a reduced dose of irinotecan, based on UGT1A1 polymorphism, compared to the standard dose (i.e., 126 mg/m2vs. 180 mg/m2) had slightly higher exposure to SN38, but that the incidence of toxicities (grade 4 neutropenia, febrile neutropenia, and diarrhoea) was comparable across the groups.