Effects of CYP3A inhibitors on the pharmacokinetics of quizartinib, a potent and selective FLT3 inhibitor, and its active metabolite

AIMS: Quizartinib is an oral, highly potent and selective next‐generation FMS‐like tyrosine kinase 3 (FLT3) inhibitor under investigation in patients with FLT3‐internal tandem duplication‐mutated acute myeloid leukaemia. This drug–drug interaction study assessed the pharmacokinetics (PK) of quizartinib when coadministered with strong or moderate cytochrome P450 3A (CYP3A) inhibitors. METHODS: In this parallel‐group study, subjects were randomised to receive: (i) quizartinib + ketoconazole; (ii) quizartinib + fluconazole; or (iii) quizartinib alone. On Days 1–28, subjects received ketoconazole 200 mg or fluconazole 200 mg twice daily, and on Day 8, all subjects received a single 30‐mg quizartinib dose. Blood samples were collected for PK analyses, steady‐state PK parameters were simulated by superpositioning, and safety was assessed. RESULTS: Ninety‐three healthy subjects were randomised; 86 completed the study. When administered with ketoconazole, geometric mean ratios (90% confidence interval) for quizartinib maximum observed plasma concentration (C(max)) and area under the plasma concentration–time curve (AUC) from time 0 extrapolated to infinity were 117% (105%, 130%) and 194% (169%, 223%), respectively, vs quizartinib alone. Steady‐state PK simulation demonstrated ~2‐fold increase of both steady–state C(max) and AUC from time 0 to the end of the dosing interval when quizartinib was administered with ketoconazole due to accumulation of quizartinib at steady state. When administered with fluconazole, geometric mean ratios (90% confidence interval) for quizartinib C(max) and AUC from time 0 extrapolated to infinity were 111% (100%, 124%) and 120% (104%, 138%), respectively, vs quizartinib alone. Overall, 5.4% of subjects experienced quizartinib‐related adverse events; no serious adverse events or deaths occurred. CONCLUSIONS: These results suggest reducing the dose of quizartinib when coadministered with a strong CYP3A inhibitor, but not with a moderate or weak CYP3A inhibitor. This dose reduction was implemented in phase 3 evaluation of quizartinib.