Sorafenib Dose Recommendation in Acute Myeloid Leukemia Based on Exposure‐FLT3 Relationship

Sorafenib administered at the approved dose continuously is not tolerated long‐term in patients with acute myeloid leukemia (AML). The purpose of this study was to optimize the dosing regimen by characterizing the sorafenib exposure‐response relationship in patients with AML. A one‐compartment model with a transit absorption compartment and enterohepatic recirculation described the exposure. The relationship between sorafenib exposure and target modulation of kinase targets (FMS‐like tyrosine kinase 3 (FLT3)‐ITD and extracellular signal‐regulated kinase (ERK)) were described by an inhibitory maximum effect (E(max)) model. Sorafenib could inhibit FLT3‐ITD activity by 100% with an IC(50) of 69.3 ng/mL and ERK activity by 84% with an IC(50) of 85.7 ng/mL (both adjusted for metabolite potency). Different dosing regimens utilizing 200 or 400 mg at varying frequencies were simulated based on the exposure‐response relationship. Simulations demonstrate that a 200 mg twice daily (b.i.d.) dosing regimen showed similar FLT3‐ITD and ERK inhibitory activity compared with 400 mg b.i.d. and is recommended in further clinical trials in patients with AML.