Based on this evidence, the United States (US) Food and Drug Administration (FDA) amended the irinotecan label in 2005 to include UGT1A1*28/*28 as a risk factor for severe neutropenia, stating that when administered as a single-agent, a reduction in the starting dose by at least one level or irinotecan hydrochloride injection should be considered for patients known to be homozygous for the UGT1A1*28 allele [138]. The gene discussed is UGT1A1; the disease is neutropenia.