Linking the Gastrointestinal Behavior of Ibuprofen with the Systemic Exposure between and within Humans—Part 2: Fed State

Bridging the Gap between Food Effects under Clinical Trial Conditions and Real Life: Modeling Delayed Gastric Emptying of Drug Substances and Gastric Content Volume Based on Meal Characteristics

Delayed gastric emptying is known to have a major impact on drug absorption. While the test meal recommended by the FDA and EMA to study food effects represents a worst-case scenario, it does not reflect the reality of the patients. Physiologically based pharmacokinetic (PBPK) models could bridge the gap between clinical settings of food effect studies and the diverse nonclinical situations by simulating the effect of meals with different compositions and volumes. A mathematical equation based on a stretched exponential function was reparameterized to describe the gastric emptying process of mixed solid meals. The model was fitted to literature data including the gastric emptying data of 23 meals from 15 studies. Using a multiple linear regression model, we were able to predict the two function parameters from the meal characteristics caloric content and the percentage of calories derived from fat. After implementation into the PBPK software PK-Sim, the model, together with a separate compartment for liquid gastric contents, was compared to commercially available software. The model is able to simulate the gastric emptying of mixed solid meals containing drugs based on specific meal characteristics. A second compartment allows for distribution between liquid and solid components and rapid gastric emptying along the Magenstrasse.

Food effects on gastrointestinal physiology and drug absorption

Food ingestion affects the oral absorption of many drugs in humans. In this review article, we summarize the physiological factors in the gastrointestinal (GI) tract that affect the in vivo performance of orally administered solid dosage forms in fasted and fed states in humans. In particular, we discuss the effects of food ingestion on fluid characteristics (pH, bile concentration, and volume) in the stomach and small intestine, GI transit of water and dosage forms, and microbiota. Additionally, case examples of food effects on GI physiology and subsequent changes in oral drug absorption are provided. Furthermore, the effects of food, especially fruit juices (e.g., grapefruit, orange, apple) and green tea, on transporter-mediated permeation and enzyme-catalyzed metabolism of drugs in intestinal epithelial cells are also summarized comprehensively.

Improving Dissolution Behavior and Oral Absorption of Drugs with pH-Dependent Solubility Using pH Modifiers: A Physiologically Realistic Mass Transport Analysis

Orally dosed drugs must dissolve in the gastrointestinal (GI) tract before being absorbed through the epithelial cell membrane. In vivo drug dissolution depends on the GI tract's physiological conditions such as pH, residence time, luminal buffers, intestinal motility, and transit and drug properties under fed and fasting conditions (Paixão, P. et al. Mol. Pharm. 2018 and Bermejo, et al. M. Mol. Pharm. 2018). The dissolution of an ionizable drug may benefit from manipulating in vivo variables such as the environmental pH using pH-modifying agents incorporated into the dosage form. A successful example is the use of such agents for dissolution enhancement of BCS class IIb (high-permeability, low-solubility, and weak base) drugs under high gastric pH due to the disease conditions or by co-administration of acid-reducing agents (i.e., proton pump inhibitors, H2-antagonists, and antacids). This study provides a rational approach for selecting pH modifiers to improve monobasic and dibasic drug compounds' dissolution rate and extent under high-gastric pH dissolution conditions, since the oral absorption of BCS class II drugs can be limited by either the solubility or the dissolution rate depending on the initial dose number. Betaine chloride, fumaric acid, and tartaric acid are examples of promising pH modifiers that can be included in oral dosage forms to enhance the rate and extent of monobasic and dibasic drug formulations. However, selection of a suitable pH modifier is dependent on the drug properties (e.g., solubility and pK_a) and its interplay with the pH modifier pK_a or pK_as. As an example of this complex interaction, for basic drugs with high pK_a and intrinsic solubility values and large doses, a polyprotic pH modifier can be expected to outperform a monoacid pH modifier. We have developed a hierarchical mass transport model to predict drug dissolution of formulations under varying pH conditions including high gastric pH. This model considers the effect of physical and chemical properties of the drug and pH modifiers such as pK_a, solubility, and particle size distribution. This model also considers the impact of physiological conditions such as stomach emptying rate, stomach acid and buffer secretion, residence time in the GI tract, and aqueous luminal volume on drug dissolution. The predictions from this model are directly applicable to in vitro multi-compartment dissolution vessels and are validated by in vitro experiments in the gastrointestinal simulator. This model's predictions can serve as a potential data source to predict plasma concentrations for formulations containing pH modifiers administered under the high-gastric pH conditions. This analysis provides an improved formulation design procedure using pH modifiers by minimizing the experimental iterations under both in vitro and in vivo conditions.

Leveraging Oral Drug Development to a Next Level: Impact of the IMI-Funded OrBiTo Project on Patient Healthcare

A thorough understanding of the behavior of drug formulations in the human gastrointestinal (GI) tract is essential when working in the field of oral drug development in a pharmaceutical company. For orally administered drug products, various GI processes, including disintegration of the drug formulation, drugrelease, dissolution, precipitation, degradation, dosage form transit and permeation, dictate absorption into the systemic circulation. These processes are not always fully captured in predictive in vitro and in silico tools, as commonly applied in the pre-clinical stage of formulation drug development. A collaborative initiative focused on the science of oral biopharmaceutics was established in 2012 between academic institutions and industrial companies to innovate, optimize and validate these in vitro and in silico biopharmaceutical tools. From that perspective, the predictive power of these models can be revised and, if necessary, optimized to improve the accuracy toward predictions of the in vivo performance of orally administered drug products in patients. The IMI/EFPIA-funded "Oral Bioavailability Tools (OrBiTo)" project aimed to improve our fundamental understanding of the GI absorption process. The gathered information was integrated into the development of new (or already existing) laboratory tests and computer-based methods in order to deliver more accurate predictions of drug product behavior in a real-life setting. These methods were validated with the use of industrial data. Crucially, the ultimate goal of the project was to set up a scientific framework (i.e., decision trees) to guide the use of these new tools in drug development. The project aimed to facilitate and accelerate the formulation development process and to significantly reduce the need for animal experiments in this area as well as for human clinical studies in the future. With respect to the positive outcome for patients, high-quality oral medicines will be developed where the required dose is well-calculated and consistently provides an optimal clinical effect. In a first step, this manuscript summarizes the setup of the project and how data were collected across the different work packages. In a second step, case studies of how this project contributed to improved knowledge of oral drug delivery which can be used to develop improved products for patients will be illustrated.

Toward Developing Discriminating Dissolution Methods for Formulations Containing Nanoparticulates in Solution: The Impact of Particle Drift and Drug Activity in Solution

Enabling formulations are an attractive approach to increase the dissolution rate, solubility, and oral bioavailability of poorly soluble compounds. With the growing prevalence of poorly soluble drug compounds in the pharmaceutical pipeline, supersaturating drug delivery systems (SDDS), a subset of enabling formulations, have grown in popularity due to their properties allowing for drug concentrations greater than the corresponding crystalline solubility. However, the extent of supersaturation generated as the enabling formulation traverses the gastrointestinal (GI) tract is dynamic and poorly understood. The dynamic nature of supersaturation is a result of several competing kinetic processes such as dissolution, solubilization by formulation and endogenous surfactants, crystallization, and absorption. Ultimately, the free drug concentration, which is equivalent to the drug's inherent thermodynamic activity amid these kinetic processes, defines the true driving force for drug absorption. However, in cases where solubilizing agents are present (i.e., surfactants and bile salts), drug molecules may associate with colloidal nanoscale species, complicating drug activity determination. These nanoscale species can drift into the aqueous boundary layer (ABL), increasing the local API activity at the membrane surface, resulting in increased bioavailability. Herein, a novel approach was developed to accurately measure thermodynamic drug activity in complex media containing drug distributed in nanoparticulate species. This approach captures the influence of the ABL on the observed flux and, ultimately, the predicted unbound drug concentration. The results demonstrate that this approach can help to (1) measure the true extent of local supersaturation in complex systems containing solubilizing excipients and (2) elucidate the mechanisms by which colloidal aggregates can modulate the drug activity in solution and potentially enhance the flux observed across a membrane. The utilization of these techniques may provide development scientists with a strategy to evaluate formulation sensitivity to nanospeciation and allow formulators to maximize the driving force for absorption in a complex environment, perhaps enabling the development of dissolution methods with greater discrimination and correlation to pre-clinical and clinical data sets.

Best Practices in the Development and Validation of Physiologically Based Biopharmaceutics Modeling. A Workshop Summary Report

This workshop report summarizes the proceedings of Day 2 of a three-day workshop on "Current State and Future Expectations of Translational Modeling Strategies toSupportDrug Product Development, Manufacturing Changes and Controls". From a drug product quality perspective, physiologically based biopharmaceutics modeling (PBBM) is a tool to link variations in the drug product quality attributes to in vivo outcomes enabling the establishment of clinically relevant drug product specifications (CRDPS). Day 2 of the workshop focused on best practices in developing, verifying and validating PBBM. This manuscript gives an overview of podium presentations and summarizes breakout (BO) session discussions related to (1) challenges and opportunities for using PBBM to assess the clinical impact of formulation and manufacturing changes on the in vivo performance of a drug product, (2) best practices to account for parameter uncertainty and variability during model development, (3) best practices in the development, verification and validation of PBBM and (4) opportunities and knowledge gaps related to leveraging PBBM for virtual bioequivalence simulations.

The Introduction of a New Flexible In Vivo Predictive Dissolution Apparatus, GIS-Alpha (GIS-α), to Study Dissolution Profiles of BCS Class IIb Drugs, Dipyridamole and Ketoconazole

The physiological pH changes and peristalsis activities in gastrointestinal (GI) tract have big impact on the dissolution of oral drug products, when those oral drug products include APIs with pH-dependent solubility. It is well documented that predicting the bioperformance of those oral drug products can be challenging using compendial methods. To overcome this limitation, in vivo predictive dissolution apparatuses, such as the transfer model, have been developed to predict bioperformance of oral formulation candidates and drug products. In this manuscript we utilize a new transfer-model dissolution apparatus, the gastrointestinal simulator-α (GIS-α), to characterize its behavior in terms of transfer kinetics and pH, assess its reproducibility and adaptability to mimic different transfer conditions, as well as study dissolution of ketoconazole and dipyridamole as model BCS class IIb compounds. Availability of commercially available dissolution transfer systems with similar configuration to compendial dissolution apparatus, may be helpful to simplify and standardize in vivo predictive dissolution methodologies for BCS class IIb compounds in the future.

Application of the Gastrointestinal Simulator (GIS) Coupled with In Silico Modeling to Measure the Impact of Coca-Cola® on the Luminal and Systemic Behavior of Loratadine (BCS Class 2b)

In the present work, we explored if Coca-Cola^® had a beneficial impact on the systemic outcome of the weakly basic drug loratadine (Wal-itin^®, immediate-release formulation, 10 mg, generic drug product). To map the contribution of underlying physiological variables that may positively impact the intestinal absorption of loratadine, a multi-compartmental and dynamic dissolution device was built, namely the Gastrointestinal Simulator (GIS). The luminal behavior of one immediate-release (IR) tablet of 10 mg of loratadine was tested under four different fasted state test conditions in the GIS: (i) with 250 mL of water and applying a predetermined gastric half-life (t_1/2,G) of 15 min; (ii) with 250 mL of water and applying a t_1/2,G of 30 min; (iii) with 250 mL of Coca-Cola^® and a t_1/2,G of 15 min; (iv) with 250 mL of Coca-Cola^® and a t_1/2,G of 30 min. After initiating the experiments, solution concentrations and solubility were measured in the withdrawn samples, and pH was monitored. To address the impact of the present CO₂ in Coca-Cola^® on the disintegration time of the tablet, additional disintegration experiments were performed in a single-vessel applying tap water and sparkling water as dissolution media. These experiments demonstrated the faster disintegration of the tablet in the presence of sparkling water, as the present CO₂ facilitates the release of the drug. The buffer capacity of Coca-Cola^® in the presence of FaSSGF was 4-fold higher than the buffer capacity of tap water in the presence of FaSSGF. After performing the in vitro experiments, the obtained results were used as input for a two-compartmental pharmacokinetic (PK) modeling approach to predict the systemic concentrations. These simulations pointed out that (i) the present CO₂ in Coca-Cola^® is responsible for the enhancement in drug release and dissolution and that (ii) a delay in gastric emptying rate will sustain the supersaturated concentrations of loratadine in the intestinal regions of the GI tract, resulting in an enhanced driving force for intestinal absorption. Therefore, co-administration of loratadine with Coca-Cola^® will highly likely result in an increased systemic exposure compared to co-administration of loratadine with tap water. The mechanistic insights that were obtained from this work will serve as a scientific basis to evaluate the impact of Coca-Cola^® on the systemic exposure of weakly basic drugs for patients on acid-reducing agents in future work.

Exploring the impact of real-life dosing conditions on intraluminal and systemic concentrations of atazanavir in parallel with gastric motility recording in healthy subjects

This work strived to explore gastrointestinal (GI) dissolution, supersaturation and precipitation of the weakly basic drug atazanavir in humans under different 'real-life' intake conditions. The impact of GI pH and motility on these processes was thoroughly explored. In a cross-over study, atazanavir (Reyataz®) was orally administered to 5 healthy subjects with (i) a glass of water, (ii) a glass of Coca-Cola® and (iii) a glass of water under hypochlorhydric conditions (induced by concomitant intake of a proton-pump inhibitor (PPI)). After intake, GI fluids were aspirated from the stomach and the duodenum and, subsequently, analyzed for atazanavir. In parallel, blood samples were collected to assess systemic concentrations. In general, the results of this study revealed that the acidic gastric pH in combination with gastric residence time played a crucial role in the dissolution of atazanavir along the GI tract. After intake of atazanavir with a glass of water (i.e., reference condition), complete gastric dissolution was observed. After GI transfer, supersaturation was noticed for a limited amount of time (1.25 h). With respect to the Coca-Cola® condition, complete gastric dissolution was also observed. A delay in gastric emptying, highly likely caused by the caloric content (101 kcal), was responsible for delayed arrival of atazanavir into the upper small intestine, creating a longer time window of supersaturated concentrations in the duodenal segment (3.25 h) compared to the water condition. The longer period of supersaturated concentrations resulted in a slightly higher systemic exposure of atazanavir compared to the condition when atazanavir was taken with a glass of water. A remarkable observation was the creation (when the drug was given in the migrating motor complex (MMC) phase 2) or maintenance (when the drug was given in MMC phase 1) of a quiescent phase for up to 80 min. With respect to the PPI condition, negligible gastric and intestinal concentrations were observed, resulting in minimal systemic exposure for all subjects. It can be concluded that gastric pH and residence time play a pivotal role in the intestinal disposition of atazanavir in order to generate sufficiently high concentrations further down in the intestinal tract for a sufficient period of time, thus creating a beneficial driving force for intestinal absorption.