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.