Semimechanistic pharmacokinetic–pharmacodynamic model of tripegfilgrastim for pediatric patients after chemotherapy

Tripegfilgrastim is a long-acting granulocyte colony-stimulating factor (G-CSF) that has been used to prevent chemotherapy-induced neutropenia in adults. This study aimed to establish a pharmacokinetic (PK)–pharmacodynamic (PD) model to explore the impact of chemotherapy and tripegfilgrastim on absolute neutrophil counts (ANCs) and to further propose a fixed-dose regimen in pediatric patients. Because neutrophils affect the clearance of tripegfilgrastim, the semimechanistic PK-PD model was developed simultaneously by using data from 40 healthy adults and 27 pediatric patients with solid tumors. Tripegfilgrastim PK and ANC dynamics were described with a pharmacodynamics-mediated drug disposition model assuming quasi-equilibrium with five transit compartments mimicking neutrophil granulopoiesis. The effect of chemotherapy on neutrophils was included by stimulating the elimination of the G-CSF receptor at the mitotic cells. Healthy adult and pediatric patients showed significantly different value for dissociation constant of the tripegfilgrastim-G-CSF receptor complex (K_d) and apparent volume of distribution (V_d/F). Patients treated with chemotherapy had a higher V_d/F and 62% lower K_d than healthy adults. As the age increased, the absorption rate of tripegfilgrastim was decreased. Body weight affected the G-CSF receptor-mediated internalization of tripegfilgrastim, and the baseline ANC value impacted the production rate of G-CSF receptors. Simulations from the developed model suggested that 1.5, 2.5, 4, and 6 mg single subcutaneous tripegfilgrastim doses for the respective weight groups of 10–20, 21–30, 31–44, and more than 45 kg significantly reduced the duration of Grade 4 neutropenia similar to tripegfilgrastim weight-based treatment with 100 μg/kg.