Dosing of Venetoclax in Pediatric Patients with Relapsed Acute Myeloid Leukemia: Analysis of Developmental Pharmacokinetics and Exposure-Response Relationships

Abstract

This work aimed to characterize the pharmacokinetics and exposure-response relationships of venetoclax in pediatric patients with relapsed or refractory (R/R) acute myeloid leukemia (AML) to identify venetoclax doses to be administered to pediatric patients in the phase 3 study. Data from 121 patients across three phase 1 studies enrolling pediatric patients with R/R malignancies were utilized to develop a population pharmacokinetic model to describe venetoclax pharmacokinetics in pediatric patients. Individual patient average venetoclax plasma concentration up to the event of interest, derived based on the population pharmacokinetics analysis, was used to evaluate the exposure-response relationships to efficacy (complete response) and safety (neutropenia and thrombocytopenia) endpoints for patients with AML who received venetoclax in combination with azacitidine, decitabine, or cytarabine (n = 36). The population pharmacokinetic model was then used to simulate exposures in pediatric age- and weight-based subgroups to identify the venetoclax doses for pediatric patients. The pharmacokinetic data were adequately described by the two-compartment population pharmacokinetic model with first-order absorption and elimination. The model accounted for cytochrome P450 3A developmental changes using a maturation function and incorporated allometric scaling to account for growth and body size effect. Weight was identified as a statistically significant covariate on clearance and volume of distribution and retained in the final model. Population pharmacokinetic estimates were comparable to previously reported estimates in adults. Exposure-response analyses suggested that the clinical efficacy of venetoclax in combination with high-dose cytarabine (HDAC) is maximized at 600 mg adult-equivalent, and higher doses are unlikely to enhance clinical efficacy. Venetoclax 600 mg adult-equivalent was selected for further development in combination with HDAC. Additionally, venetoclax 400 mg adult-equivalent was selected for bridging/maintenance therapy in combination with azacitidine. Flat exposure-response relationships were observed with Grade ≥3 neutropenia and thrombocytopenia. Doses were selected based on weight (allometric scaling) for children aged ≥2 years old and based on weight and CYP3A ontogeny for children aged <2 years. The selected age- and weight-based dosing scheme of venetoclax is projected to achieve venetoclax exposures in pediatric subgroups comparable to those observed in adults receiving venetoclax 400 mg or 600 mg. This work characterized the pharmacokinetics and exposure-response relationships of venetoclax in pediatric patients and guided the selection of pediatric dosing regimens in support of the venetoclax phase 3 trial in pediatric AML (NCT05183035). NCT03236857, NCT03181126, and NCT03194932.