Browsing by Subject "absorption"
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(2015)Prodrugs are pharmacologically inactive molecules which undergo metabolic bioactivation in vivo to form pharmaceutically active agents. Prodrugs have been designed to improve so called drug-like properties of active parent compounds (APC) i.e. to increase solubility or absorption and to reduce first-pass metabolism etc. In this master's thesis the goal was to establish non-cell-based in vitro methods to study prodrug bioactivation. Four commercially available prodrugs (bambuterol, olmesartan medoxomil (OM), candesartan cilexetil (CC) and famciclovir) were used as test compounds. The prodrugs were incubated in liver and intestinal S9 fractions and blood plasma to study in vitro bioactivation of these prodrugs. Other metabolism of the prodrug and APC (nonproductive metabolism) was studied by comparing incubation with and without cofactors of metabolizing enzymes. Species differences was studied using human, rat and dog matrices. Prodrug concentrations were quantified from the incubation samples using liquid chromatography- tandem mass spectrometry (LC-MSMS) methods developed for this study. Additionally the effect of promoiety on passive permeability was studied with parallel artificial membrane permeability assay (PAMPA). All of the studied prodrugs produced at least low concentrations of APC in one or more incubations. Terbutaline (APC of bambuterol) formation was observed in human plasma and was concentration dependent which is consisted with the literature. Olmesartan and candesartan were formed in S9 fraction in high rate, but not in buffer: indicating enzyme mediated hydrolysis. However, based on literature CC hydrolysis was not expected to occur in intestinal S9 fractions. Penciclovir (APC of famciclovir) was formed only in presence of human or rat liver S9 fraction which was in line with the pre-existing literature. With the method used the nonproductive metabolism could not be estimated. In PAMPA bambuterol, famciclovir and OM had higher permeability than corresponding APCs whereas CC was only more permeable than candesartan in pH 7.4. The in vitro incubation used in this study can be used for screening prodrugs. However both low and high activation rates were observed thus the clinically relevant in vivo APC formation can be achieved with both high and low bioactivation in vitro. Studying the rate of prodrug formation alone estimations about clinically relevant bioactivation rates cannot be concluded. No clear signs of nonproductive could be seen with the prodrugs studied with current method. For the estimation of nonproductive metabolism, metabolite screening studies would need to be developed and conducted parallel to studies prescribed in this master's thesis.
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(2023)Physiologically based pharmacokinetic modelling (PBPK) can be used to predict pharmacokinetic behaviour of new drug molecules in human. PBPK model represents the body anatomically and physiologically with compartments connected to each other and combines those to drug specific parameters. PBPK modelling can be used to predict the absorption, disposition, and time-concentration profiles of drug molecules. The purpose of the study was to build a PBPK model for new drug molecule under research (compound A) and predict pharmacokinetics in human, to support the selection of dosing interval, formulation, and sampling time points for the first clinical trial. In this work it is described the building of the model in the ”bottom-up”-approach using in vitro parameters in GastroPlusTM-software. The modelling was done also for preclinical species (mouse, rat, dog) comparing the simulations to the observed in vivo data, which gave the confidence to the methods used in the modelling also for human. The model was first built for systemic kinetics and thereafter it was used for predicting pharmacokinetics after oral dosing. Parameters of systemic kinetics were compared also to the predictions from allometric scaling. Based on the preclinical species the most predictive method for the volume of distribution of compound A was the method by Lukacova, which predicted the volume of distribution to be moderate in human (1.7 l/kg). From the in vitro-to-in vivo -extrapolation methods the most predictive method to predict the clearance was the method by Poulin, which predicted low clearance in human (8.1-14.3 l/h). Empirical scaling factors based on the preclinical data were not needed, as the models predicted well the observed in vivo data. Allometric methods predicted the systemic kinetic parameters to be in the similar range. Advanced compartmental absorption transit -model (ACAT) integrated to GastroPlusTM-software predicted the absorption after oral dosing well in the preclinical species (predicted/observed ratio 0.8-1.3 for systemic exposure) despite the low solubility of the compound A. The model predicted the absorption in human to be sensitive to particle size and absorption rate to be clearly affected by the particle size. The feeding status was also predicted to affect on the absorption with larger particle sizes. The gut metabolism was not predicted to limit the oral exposure notably, whereas moderate bioavailability was predicted to be achievable. Compound A could be given in a capsule if the target particle size distribution could be achieved. The built PBPK-model can be used in the future to predict the first clinical doses by comparing the predicted plasma concentrations to in vitro pharmacodynamic parameters and to the plasma concentrations needed for efficacy in the pharmacodynamic models. The model can also be used to predict the drug-drug interactions.
Now showing items 1-2 of 2