Infliximab in paediatric inflammatory bowel disease: External evaluation of population pharmacokinetic models.

AIMS: Use of infliximab (IFX) has improved outcomes in children with inflammatory bowel disease (IBD). However, a proportion of patients does not respond to IFX or loses response over time. Population pharmacokinetic (PopPK) modelling is a promising approach for IFX dose optimization, but with the increasing number of PopPK models in literature, model evaluation is essential. The aims of this study are: (i) to validate the predictive performance of existing IFX PopPK models using a cohort of children with IBD; and (ii) to perform a Bayesian estimation of the most suitable model to predict the next IFX concentrations. METHODS: PubMed was searched for IFX PopPK models in children. Selected models were rebuilt and analysed using R. Model performance was assessed through goodness-of-fit-plots, residuals against time, prediction error and prediction-corrected visual predictive checks. The validation cohort consisted of 73 children with IBD who were treated with IFX in our centre between 2017 and 2023 (340 IFX measurements). RESULTS: We identified 9 PopPK models. Model bias for individual predicted values ranged from -9.29% to 8.01% compared to bias for population predicted values. The model by Vande Casteele et al. demonstrated superior performance (individual predicted bias 2.13, population predicted bias -6.11); upon Bayesian estimation, it predicted induction trough levels with median error of 12.95% but had a median error of -69% predicting maintenance concentrations. CONCLUSION: The model by Vande Casteele et al. displayed superior performance in initial evaluations but had a high error in estimating next IFX levels and can only be used in practice to predict induction levels.

Gemcitabine and epirubicin plasma concentration-related excretion in saliva in patients with non-small cell lung cancer.

AIM: The excretion in saliva of gemcitabine and its metabolite 2',2'-difluorodeoxyuridine (dFdU) as well as epirubicin (Epi) and its metabolite epirubicinol (Epi-ol) was studied in patients with non-small cell lung cancer, treated with gemcitabine plus epirubicin. METHODS: Patients (n = 12) were treated with gemcitabine 1125 mg/m, followed by Epi 100 mg/m. Blood, saliva, and oral mucosa cells were collected during 22 hours for analysis of gemcitabine, Epi, and their metabolites. Gemcitabine, dFdU, Epi, and Epi-ol were quantified by high-performance liquid chromatography. RESULTS: Gemcitabine was cleared rapidly from plasma and undetectable after 3 hours in all patients. Gemcitabine was detectable in saliva during only the first hour after infusion. The Cmax in saliva was 0.66 +/- 0.61 mg/L, and the saliva to plasma ratio (S/P ratio) was 0.038 +/- 0.037. The Cmax of dFdU was reached 1.5-2 hours after gemcitabine infusion and was 1.03 +/- 0.63 mg/L. The dFdU S/P ratios gradually increased from 0.021 +/- 0.013 at t = 1 hour to 0.050 +/- 0.027 at t = 6 hours after infusion. Epi displayed a triexponential plasma concentration-time profile. The Epi and Epi-ol concentrations in saliva at t = 6 hours after administration were 55 +/- 27 and 9 +/- 9 microg/L, respectively, and decreased to 28 +/- 14 and 7 +/- 4 microg/L, respectively, at t = 22 hours. The corresponding S/P ratios were 1.28 +/- 0.73 and 0.36 +/- 0.31 at t = 6 hours and 1.72 +/- 1.00 and 0.62 +/- 0.34 at t = 22 hours, respectively. The amount of Epi in mucosal cells ranged from 135-598 ng per 10 cells at t = 3 hours and decreased to 33-196 ng per 10 cells at t = 22 hours. CONCLUSION: Gemcitabine and Epi, as well as their main metabolites dFdU and Epi-ol, are excreted in detectable amounts in saliva, although their absolute concentrations remain relatively low.