Open Label Study to Evaluate Safety and Efficacy of 2 Doses of Quizartinib in Patients With Relapsed or Refractory Acute Myeloid Leukemia

Inclusion Criteria: * Subject has morphologically documented primary acute myeloid leukemia (AML) or AML secondary to myelodysplastic syndrome (MDS) as defined by the World Health Organization (WHO) criteria, as determined by pathology review at the treating institution and has relapsed or is refractory after 1 second line (salvage) regimen or after hematopoietic stem cell transplantation (HSCT) * Subject is positive for FLT3-ITD activating mutation in bone marrow or peripheral blood (\>10% allelic ratio) * Eastern Cooperative Oncology Group performance status of 0 to 2 * In the absence of rapidly progressing disease clearly documented by the investigator, the interval from prior treatment to time of AC220 administration will be at least 2 weeks (14 days) for prior cytotoxic agents or at least 5 half-lives for prior noncytotoxic agents, including immunosuppressive therapy post HSCT * Persistent chronic clinically significant nonhematological toxicities from prior treatment (including chemotherapy, kinase inhibitors, immunotherapy, experimental agents, radiation, HSCT, or surgery) must be Grade ≤ 1 * Patients - both males and females - with reproductive potential are eligible Exclusion Criteria: * Subject received previous treatment with AC220 * Subject has a diagnosis of acute promyelocytic leukemia * Subject has a diagnosis of chronic myelogenous leukemia (CML) in blast crisis * Subject has AML or antecedent MDS secondary to prior chemotherapy * Subject has had HSCT and has either of the following: * Donor lymphocyte infusion (DLI) is not permitted during the study or \< 30 days prior to study entry * Subject has clinically active central nervous system (CNS) leukemia. A subject is considered eligible if CNS leukemia is controlled and subject is receiving intrathecal (IT) therapy at study entry. Subjects should continue to receive IT therapy (or cranial radiation) as clinically indicated * Subject has received concurrent chemotherapy, immunotherapy, or radiotherapy within 14 days prior to the first dose of AC220, or any ancillary therapy that is considered to be investigational (i.e., used for non-approved indications(s) and in the context of a research investigation) within 30 days or 5 half-lives (whichever is longer) prior to the first dose of study drug * Subject requires treatment with concomitant drugs that prolong QT/QTc interval or with strong inhibitors or inducers of cytochrome P450- isozyme3A4 (CYP3A4) with the exception of antibiotics, antifungals, and antivirals that are used as standard of care post-transplant or to prevent or treat infections and other such drugs that are considered absolutely essential for the care of the subject * Subject requires treatment with anticoagulant therapy * Subject has a known positive test for human immunodeficiency virus, hepatitis C, or hepatitis B surface antigen * Subject had major surgery within 4 weeks prior to first dose of AC220 * Subject has uncontrolled or significant cardiovascular disease, including * Subject has a pre-existing disorder predisposing the subject to a serious or life-threatening infection (e.g. cystic fibrosis, congenital or acquired immunodeficiency, bleeding disorder, or cytopenias not related to AML) * Subject has an active uncontrolled acute or chronic systemic fungal, bacterial, viral, or other infection * Subject has any of the following laboratory values: * Subject is a female with a positive pregnancy test, pregnant, or breastfeeding * Subject has any medical, psychiatric, addictive or other kind of disorder which compromises the ability of the subject to give written informed consent and/or to comply with procedures