Investigating the Mechanisms behind the Positive Food Effect of Abiraterone Acetate: In Vitro and Rat In Situ Studies.

The anticancer agent abiraterone suffers from an extensive positive food effect after oral intake of the prodrug abiraterone acetate (Zytiga). The underlying processes determining postprandial abiraterone absorption were investigated in this study. The impact of lipids and lipid digestion products on (i) the solubility of abiraterone acetate and abiraterone, (ii) the conversion of abiraterone acetate to abiraterone, and (iii) the passive permeation of abiraterone was determined in vitro. The interaction of abiraterone acetate and abiraterone with vesicles and colloidal structures in the simulated fed state media containing undigested lipids and lipid digestion products enhanced the solubility of both compounds but limited the esterase-mediated hydrolysis of abiraterone acetate and the potential of abiraterone to permeate. Rat in situ intestinal perfusion experiments with a suspension of abiraterone acetate in static fed state simulated media identified abiraterone concentrations in the perfusate as the main driving force for absorption. However, experiments with ongoing lipolysis in the perfusate highlighted the importance of including lipid digestion as a dynamic process when studying postprandial abiraterone absorption. Future research may employ the in situ perfusion model to study postprandial drug absorption from a dynamic lipolysis-mediated intestinal environment to provide reference data for the optimisation of relevant in vitro models to evaluate food effects.

Orlistat disposition in the human jejunum and the effect of lipolysis inhibition on bile salt concentrations and composition.

The lipolysis-mediated postprandial small intestinal environment is known to influence the solubilisation and subsequent absorption of lipophilic drugs. In a previously performed small-scale clinical study in healthy volunteers, co-administration of the lipase inhibitor orlistat increased jejunal solubilisation and systemic absorption of fenofibrate after intake of the lipid-based formulation Fenogal. In the present study, the jejunal disposition of the locally acting orlistat was assessed and linked to fenofibrate solubilisation. In addition, the effect of orlistat-induced lipolysis inhibition on bile salt concentrations and composition was evaluated. Orlistat was distributed predominantly in the lipid layer, as indicated by a 5- to 14-fold higher AUC0-320 min in the total jejunal samples as compared to the micellar layers. No effect of orally administered orlistat on bile salt composition or total concentrations (ranging from 1.5 to 24.8 mM and 1.8 to 33.2 mM with and without orlistat co-administration, respectively) could be observed. The intraluminal presence of orlistat in the total jejunal samples correlated with the increased fenofibrate solubilisation in the jejunum (r = 0.9344) and enhanced absorption (r = 0.8184), highlighting the importance of the intraluminal lipid phase in lipophilic drug absorption.

The Influence of Fed State Lipolysis Inhibition on the Intraluminal Behaviour and Absorption of Fenofibrate from a Lipid-Based Formulation.

The bioavailability of lipophilic drugs may or may not be increased when administered with food due to increased solubilisation in fed state gastrointestinal (GI) fluids. The in vivo interplay between drug solubilisation, lipid phase digestion and drug absorption is complex and remains poorly understood. This study aimed to investigate the role of fed state GI lipolysis on the intraluminal behaviour and absorption of fenofibrate, formulated as the lipid-based formulation Fenogal. Therefore, a crossover study was performed in healthy volunteers using orlistat as lipase inhibitor. Fenofibrate concentrations were determined in the proximal jejunum and linked to simultaneously assessed systemic fenofibric acid concentrations. Inhibition of lipolysis by orlistat resulted in a faster onset of absorption in 4 out of 6 volunteers, reflected by a decrease in systemic Tmax between 20 and 140 min. In addition, the increase of undigested lipids present in the small intestine upon orlistat co-administration sustained drug solubilisation for a longer period, resulting in higher fenofibrate concentrations in the jejunum and improved absorption in 5 out of 6 volunteers (median AUC0-8h 8377 vs. 5832 µM.min). Sustaining drug solubilisation in the lipid phase may thus contribute to the absorption of lipophilic drugs. More research into the different mechanisms underlying lipophilic drug absorption from fed state media at different levels of digestion is warranted.

Impact of gastrointestinal tract variability on oral drug absorption and pharmacokinetics: An UNGAP review.

The absorption of oral drugs is frequently plagued by significant variability with potentially serious therapeutic consequences. The source of variability can be traced back to interindividual variability in physiology, differences in special populations (age- and disease-dependent), drug and formulation properties, or food-drug interactions. Clinical evidence for the impact of some of these factors on drug pharmacokinetic variability is mounting: e.g. gastric pH and emptying time, small intestinal fluid properties, differences in pediatrics and the elderly, and surgical changes in gastrointestinal anatomy. However, the link of colonic factors variability (transit time, fluid composition, microbiome), sex differences (male vs. female) and gut-related diseases (chronic constipation, anorexia and cachexia) to drug absorption variability has not been firmly established yet. At the same time, a way to decrease oral drug pharmacokinetic variability is provided by the pharmaceutical industry: clinical evidence suggests that formulation approaches employed during drug development can decrease the variability in oral exposure. This review outlines the main drivers of oral drug exposure variability and potential approaches to overcome them, while highlighting existing knowledge gaps and guiding future studies in this area.

The influence of gastric motility on the intraluminal behavior of fosamprenavir.

In fasting conditions, the gastrointestinal system contracts according to the interdigestive migrating motor complex (MMC), in which phases of quiescence (MMC phase I) alternate with phases of medium (MMC phase II) to very strong (MMC phase III) contractions. The time of drug intake relative to this cyclic motility pattern may cause variations in formulation behavior. To explore this hypothesis, a cross-over study was performed in healthy volunteers with an immediate release tablet of fosamprenavir (Telzir) which was administered in either MMC phase I or MMC phase II, as determined by high-resolution manometry. In the intestinal tract, fosamprenavir is rapidly hydrolyzed to the active compound amprenavir by alkaline phosphatases. Drug concentrations of both prodrug and drug were determined in the stomach and duodenum and linked to simultaneously assessed systemic concentrations. In 5 out of 6 healthy volunteers, the gastric release of fosamprenavir and the systemic uptake of amprenavir were affected by the MMC phase in which the tablet was administered. The intragastric disintegration of the tablet was faster and less variable after administration in MMC phase II, resulting in faster and less variable uptake of amprenavir in the systemic circulation. Mean plasma tmax values were 157 (±72.0) and 73.3 (±27.3) min after administration in MMC phase I and MMC phase II, respectively. The study clearly identified the time of oral drug intake relative to the interdigestive motility pattern as a possible source of variation in gastrointestinal drug behavior and absorption.