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AimThe aim of the present study was to evaluate the pharmacokinetics of bevacizumab and various dosing strategies for this agent in paediatric patients.MethodsData were collected from 232 paediatric patients (1971 concentrations) in five studies, with a wide range of age (0.5 – 21 years), body weight (BWT; 5.9 – 125 kg), and regimens (5 – 15 mg kg–1 biweekly or triweekly). Data from 152 patients (1427 concentrations) and 80 patients (544 concentrations) were used for model building and external validation, respectively. Steady‐state exposure was simulated under BWT‐based, body surface area (BSA)‐based, ideal body weight (IBW)‐based, and tier‐based doses. NONMEM and R were used for analyses.ResultsTypical estimates of clearance, central volume of distribution (V1), and median half‐life were 9.04 ml h–1, 2851 ml, and 19.6 days, respectively. Clearance decreased with increasing albumin. Clearance and V1 increased with BWT and were higher in male patients. Clearance and V1 were lower in children with primary central nervous system (CNS) tumours than in children with sarcomas, resulting in 49% higher trough (Cmin) and 29% higher peak (Cmax) concentrations. BWT‐adjusted clearance and V1 remained unchanged across ages. Paediatric Cmin was similar to adult Cmin under all dosing strategies. Paediatric Cmax exceeded adult Cmax under tier‐based doses.ConclusionsBWT‐adjusted pharmacokinetic parameter estimates in paediatric patients were similar to those in adults, and similar across ages. Bevacizumab exposure was higher in children with primary CNS tumours than in children with sarcomas. BSA‐based, IBW‐based, and tier‐based doses offered no substantial advantage over the BWT‐based dose currently used in adults for bevacizumab. Given the similarity in pharmacokinetics among many monoclonal antibodies, this may help to develop practical paediatric dosing guidelines for other therapeutic antibodies.

BackgroundBevacizumab is approved for various cancers. This analysis aimed to comprehensively evaluate bevacizumab pharmacokinetics and the influence of patient variables on bevacizumab pharmacokinetics.MethodsRich and sparse bevacizumab serum concentrations were collected from Phase I through IV studies in early and metastatic cancers. Bevacizumab was given intravenously as single agent or in combination with chemotherapy for single- and multiple-dose schedules.ResultsModel-building used 8943 bevacizumab concentrations from 1792 patients with colon/colorectal, non-small cell lung, kidney, pancreatic, breast, prostate and brain cancer. Bevacizumab doses ranged from 1 to 20 mg/kg given once every 1, 2 or 3 weeks. A two-compartment model best described the data. The population estimates of clearance (CL), central volume of distribution (V1) and half-life for a typical 70-kg patient were 9.01 mL/h, 2.88 L and 19.6 days. CL and V1 increased with body weight and were higher in males than females by 14 and 18 %, respectively. CL decreased with increasing albumin and decreasing alkaline phosphatase. The final model was externally validated using 1670 concentrations from 146 Japanese patients that were not used for model-building. Mean prediction errors were −2.1, 3.1 and 1.0 % for concentrations, CL and V1, respectively, confirming adequate predictive performance.ConclusionsA robust bevacizumab pharmacokinetic model was developed and externally validated, which may be used to simulate bevacizumab exposure to optimize dosing strategies. Asian and non-Asian patients exhibited similar bevacizumab pharmacokinetics. Given the similarity in pharmacokinetics among monoclonal antibodies, this may inform pharmacokinetic studies in different ethnic groups for other therapeutic antibodies.Electronic supplementary materialThe online version of this article (doi:10.1007/s00280-016-3079-6) contains supplementary material, which is available to authorized users.

Obeticholic acid (OCA), a semisynthetic bile acid, is a selective and potent farnesoid X receptor (FXR) agonist in development for the treatment of chronic nonviral liver diseases. Physiologic pharmacokinetic models have been previously used to describe the absorption, distribution, metabolism, and excretion (ADME) of bile acids. OCA plasma levels were measured in healthy volunteers and cirrhotic subjects. A physiologic pharmacokinetic model was developed to quantitatively describe the ADME of OCA in patients with and without hepatic impairment. There was good agreement between predicted and observed increases in systemic OCA exposure in subjects with mild, moderate, and severe hepatic impairment, which were 1.4‐, 8‐, and 13‐fold relative to healthy volunteers. Predicted liver exposure for subjects with mild, moderate, and severe hepatic impairment were increased only 1.1‐, 1.5‐, and 1.7‐fold. In subjects with cirrhosis, OCA exposure in the liver, the primary site of pharmacological activity along with the intestine, is increased marginally (∼2‐fold).

Physiologically-based pharmacokinetic (PBPK) models are increasingly finding use in risk assessment applications of data-rich compounds. However, it is a challenge to determine the chemical-specific parameters for these models, particularly in time- and resource-limiting situations. In this regard, SARs, QSARs and QPPRs are potentially useful for computing the chemical-specific input parameters of PBPK models. Based on the frequency of occurrence of molecular fragments (CH(3), CH(2), CH, C, C=C, H, benzene ring and H in benzene ring structure) and exposure conditions, the available QSAR-PBPK models facilitate the simulation of tissue and blood concentrations for some inhaled volatile organic chemicals. The application domain of existing QSARs for developing PBPK models is limited, due to lack of relevant data for diverse chemicals and mechanisms. Even though this approach is conceptually applicable to non-volatile and high molecular weight organics as well, it is more challenging to predict the other PBPK model parameters required for modelling the kinetics of these chemicals (particularly tissue diffusion coefficients, association constants for binding and oral absorption rates). As the level of our understanding of the mechanistic basis of toxicokinetic processes improves, QSARs to provide a priori predictions of key chemical-specific PBPK parameters can be developed to expedite the internal dose-based health risk assessments in data-poor situations.