Population pharmacokinetic analysis of quizartinib in patients with newly diagnosed <scp>FLT3</scp>‐internal‐tandem‐duplication‐positive acute myeloid leukemia

The population pharmacokinetics (PK) of quizartinib and its pharmacologically active metabolite AC886 have been previously described in healthy volunteers (HV) and relapsed/refractory (R/R) FLT3-internal-tandem-duplication-positive (FLT3-IDT-positive) acute myeloid leukemia (AML) patients receiving quizartinib monotherapy. In this analysis, we characterized the population PK of quizartinib and AC886 in newly diagnosed FLT3-ITD-positive AML patients receiving standard induction and consolidation chemotherapy as background treatment, using data from the Phase 3 QuANTUM-First trial and 12 earlier studies. Quizartinib PK were best described by a three-compartment model with sequential zero- and first-order absorption and first-order elimination. A two-compartment model with first-order metabolite formation and first-order elimination best fitted AC886 data. The PK of both moieties showed large interindividual variability (approximately 70% coefficient of variation for systemic clearances). The use of strong cytochrome P450 3A (CYP3A) inhibitors had the largest impact on exposure, increasing the steady-state area under the curve during the dosing interval (AUC_ss) by 1.8-fold. This is consistent with observations in HV and R/R AML patients and confirms the need for dose adjustments during coadministration. A novel finding in newly diagnosed AML patients was the phase-dependent change in steady-state quizartinib exposure: dose-normalized AUC_ss values were 0.6-fold during induction, similar during consolidation, and 1.4-fold during continuation compared to R/R AML patients receiving quizartinib monotherapy. The present analysis highlighted the comparison of quizartinib and AC886 PK between newly diagnosed AML patients and previously studied populations, informed dose modifications needed with strong CYP3A inhibitors, and supported the use of derived individual exposure metrics in separate exposure-response analyses.