7. In the absence of rapidly progressing disease, the interval from prior treatment to time of AC220 administration will be at least 2 weeks for cytotoxic agents or at least 5 half-lives for noncytotoxic agents. The use of chemotherapeutic or antileukemic agents other than hydroxyurea is not permitted during the study with the possible exception of intrathecal (IT) therapy at the discretion of the Investigator and with the agreement of the Sponsor.