Intestinal absorption of drugs : The impact of regional permeability, nanoparticles, and absorption-modifying excipients
Abstract: For successful delivery of orally given drug products, the drug compounds must have adequate solubility and permeability in the human gastrointestinal tract. The permeability of a compound is determined by its size and lipophilicity, and is usually evaluated in various pre-clinical models, including rat models.This thesis had three major aims: 1) investigate regional permeability in human and rat intestines and evaluate two different rat models, 2) investigate the mechanisms behind absorption in nanosuspensions, and 3) investigate the effect of food on the absorption of drug molecules in solutions and suspensions, and also food’s effect on absorption modifying excipients (AMEs).Effective human permeability values obtained using regional intra-intestinal dosing and a deconvolution method agreed with values established by perfusion from the jejunum, demonstrating the accuracy and validity of the intra-intestinal bolus-dosing approach. Single-pass intestinal perfusion (SPIP) in rats showed better correlation with human effective permeability than the Ussing chamber, and was therefore deemed the better model for predicting drug permeability in humans.Absorption of microsuspensions and nanosuspension was investigated using rat SPIP, which showed that microsuspensions are subject to pronounced food effects, probably by partitioning of drug into the colloidal structures formed by bile acids, lecithin, and fatty acids. Nanosuspensions were less affected by food, which was attributed to fewer available nanoparticles in the fed state due to partitioning into colloidal structures, and because nanoparticles are able to cross the aqueous boundary layer on their own, increasing the concentration of drug adjacent to the epithelial membrane.AMEs had less effect in the fed state than the fasted state when investigated using SPIP. This difference may be caused by AMEs partitioning into luminal colloidal structures, decreasing the AMEs’ effects on the intestinal membrane. It thus seems that AMEs as well as drug compounds are subject to food-drug interactions, which may either increase or decrease the effect or absorption, something that needs to be considered during development of new drug products. In summary, this thesis has improved the knowledge of pre-clinical absorption models and the understanding of several biopharmaceutical mechanisms important for drug absorption.
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