Utilization of Gastrointestinal Simulator, an in Vivo Predictive Dissolution Methodology, Coupled with Computational Approach To Forecast Oral Absorption of Dipyridamole

Incorporating the biphasic system to GIS-α Improves In vivo prediction for low solubility drugs

The gastrointestinal simulator alpha (GIS-α) is an in vivo predictive transfer dissolution method that mimics the pH changes and peristalsis in the gastrointestinal tract, factors that are necessary in the biorelevant dissolution of drugs especially those that are under the Biopharmaceutics Classification System (BCS) class II and IV. It can be used to provide increased understanding to the dissolution, precipitation, and supersaturation of various low-solubility drugs, but lacks insights on absorption. Conducting experiments in the GIS-α with a biphasic system to add an absorptive phase in the jejunal compartment increased the observed dissolution and improved the overall in vivo prediction. In this study, the objective was to evaluate the improvement of dissolution on four representative BCS class II drugs using the biphasic format in the GIS-α. A customized double paddle was also used in the jejunal chamber to mix the aqueous buffer and organic layer simultaneously. This paddle floats in the organic layer as the aqueous volume increases and maintains the hydrodynamics in both the aqueous and organic phases. The combination of the biphasic system in the GIS-α and the moving double paddles resulted to increased dissolution profiles of fenofibrate, danazol, and celecoxib while not affecting that of ritonavir. Incorporating these dissolution profiles in a PBPK model using GastroPlus® improved the predictability of bioperformance of those oral medicines. Overall, this methodology considers both dissolution and absorption and proves to be a useful tool in predicting the in vivo performance of low-solubility drugs.

Artificial gut Simulator. A scheme to predict intestinal and plasma concentration-time profiles of a weakly basic BCS-II drug, dipyridamole

The objective of this study was to develop a scheme to predict intestinal and plasma concentration-time profiles of the weakly basic BCS-II drug, dipyridamole (DPD), using an Artificial Gut Simulator (AGS) integrated with a compartment-based disposition model. In vivo data for this study was obtained from previously published literature. A 3-compartment disposition model was developed using the plasma concentration-time profile of DPD following an intravenous bolus dose. The AGS, consisting of a donor cell and a hollow fiber-based absorption module, was tuned to absorb DPD saturated solution at a physiological rate constant, 0.0402 min-1, based on the measured Caco-2 cell monolayer permeability coefficient. The dose dumping technique commonly used during dissolution testing can generate excessively high initial supersaturation and precipitation which is not physiologically relevant. In this study, fractions of DPD dose were added incrementally every 15 min to the AGS donor to simulate an overall first-order gastric emptying process. The concentration absorbed by the hollow fiber receiver media was input into the central compartment of the disposition model. The predicted plasma concentration-time profile matched the human in vivo profile of DPD obtained after oral administration of a 50 mg dose. For 30 and 90 mg oral doses, time profiles of concentration and fraction precipitated in the AGS donor agreed well with human duodenal measurements. This study demonstrates the significance of simulating physiological rate of absorption in vitro to accurately predict the bioavailability of a BCS-II compound.

Characterization of oral drug absorption from jelly formulations: Effects of membrane permeability and intestinal fluid volume

This study aims to clarify the process of oral drug absorption from jelly formulations. Agar and pectin-based jellies containing drugs with different membrane permeability (high: antipyrine [ANT], medium: metoprolol [MET], low: atenolol [ATE]) were prepared and tested for in vitro drug release and in vivo drug absorption in rats. All drugs showed similar release profiles in vitro from both jelly formulations, except for the faster release from pectin jelly at neutral pH. In contrast, in vivo absorption of ATE but not of ANT from jelly formulations was significantly lower than from solution. Absorption of ATE and MET was low from agar jelly after oral administration, whereas additional water intake significantly increased the absorption. The process of drug absorption was described by the compartmental model consisting of jelly, intestinal fluid, and blood compartments. Drugs in the jelly diffuse into the intestinal fluid and then permeate the intestinal membrane. By considering the rate-limiting process, membrane permeability-dependent drug absorption from agar jelly and the effects of water intake were identified. In conclusion, jelly formulations may potentially decrease and delay drug oral absorption, especially of poorly permeable drugs. Intestinal fluid volume is one of the important factors to control the drug absorption.

Advancing the Harmonization of Biopredictive Methodologies through the Product Quality Research Institute (PQRI) Consortium: Biopredictive Dissolution of Dipyridamole Tablets

Biorelevant dissolution and its concept have been widely accepted and further developed to meaningfully predict the bioperformance of oral drug products. Biorelevant methodologies have been applied to design and optimize oral formulations, to facilitate formulation bridging, and to predict the outcome of bioperformance by coupling the results with modeling. Yet, those methodologies have often been independently customized to align with specific aspects of the oral drug products being developed. Therefore, the evolution of biorelevant dissolution methodologies has taken slightly diverse pathways rather than being standardized like compendial quality control (QC) methodologies. This manuscript presents an effort through the Product Quality Research Institute (PQRI, https://pqri.org) consortium entitled: the standardization of "in vivo predictive dissolution methodologies and in silico bioequivalent study working group" to find the key parameters for biorelevant dissolution, to identify the best practices, and to move toward standardization of biorelevant dissolution methodologies. This working group is composed of members from 10 pharmaceutical companies and academic institutes. The consortium project will be accomplished in five phases, whereby the first two phases have already been completed and published. In this paper, the next two phases are addressed by reporting the biorelevant dissolution profiles of dipyridamole, a weak base model drug, then incorporating the dissolution results into physiologically based biopharmaceutics modeling (PBBM) to determine whether they would lead to bioequivalence (BE) or non-BE.

Dissolution profiles of BCS class II drugs generated by the gastrointestinal simulator alpha has an edge over the compendial USP II method

The poor water solubility of orally administered drugs leads to low dissolution in the GI tract, resulting to low oral bioavailability. Traditionally, in vitro dissolution testing using the compendial dissolution apparatuses I and II has been the gold-standard method for evaluating drug dissolution and assuring drug quality. However, these methods don't accurately represent the complex physiologies of the GI tract, making it difficult to predict in vivo behavior of these drugs. In this study, the in vivo predictive method, gastrointestinal simulator alpha (GIS-α), was used to study the dissolution profiles of commercially available BCS Class II drugs, danazol, fenofibrate, celecoxib, and ritonavir. This biorelevant transfer method utilizes multiple compartments alongside peristaltic pumps, to effectively model the transfer of material in the GI tract. In all cases, the GIS-α with biorelevant buffers gave superior dissolution profiles. In silico modeling using GastroPlusTM yielded better prediction when utilizing the results from the GIS-α as input compared to the dissolution profiles obtained from the USP II apparatus. This gives the GIS-α an edge over compendial methods in generating drug dissolution profiles and is especially useful in the early stages of drug and formulation development. This information gives insight into the dissolution behavior and potential absorption patterns of these drugs which can be crucial for formulation development, as it allows for the optimization of drug delivery systems to enhance solubility, dissolution, and ultimately, bioavailability.

The Use of Global Sensitivity Analysis to Assess the Oral Absorption of Weakly Basic Compounds: A Case Example of Dipyridamole

OBJECTIVE

To utilize the global system analysis (GSA) in oral absorption modeling to gain a deeper understanding of system behavior, improve model accuracy, and make informed decisions during drug development.

METHODS

GSA was utilized to give insight into which drug substance (DS), drug product (DP), and/or physiological parameter would have an impact on peak plasma concentration (Cmax) and area under the curve (AUC) of dipyridamole as a model weakly basic compound. GSA guided the design of in vitro experiments and oral absorption risk assessment using FormulatedProducts v2202.1.0. The solubility and precipitation profiles of dipyridamole in different bile salt concentrations were measured. The results were then used to build a mechanistic oral absorption model.

RESULTS

GSA warranted further investigation into the precipitation kinetics and its link to the levels of bile salt concentrations. Mechanistic modeling studies demonstrated that a precipitation-integrated modeling approach appropriately predicted the mean plasma profiles, Cmax, and AUC from the clinical studies.

CONCLUSIONS

This work shows the value of GSA utilization in early development to guide in vitro experimentation and build more confidence in identifying the critical parameters for the mathematical models.

Development of an In Vitro Methodology to Assess the Bioequivalence of Orally Disintegrating Tablets Taken without Water

To assess the probability of bioequivalence (BE) between orally disintegrating tablets (ODTs) taken without water and conventional tablets (CTs) taken with water, an in vitro biorelevant methodology was developed using the BE Checker, which reproduces fluid shifts in the gastrointestinal tract and drug permeation. In addition to the fluid shift from the stomach to the small intestine, the process of ODT disintegration in a small amount of fluid in the oral cavity and the difference in gastric emptying caused by differences in water intake were incorporated into the evaluation protocol. Assuming a longer time to maximum plasma concentration after oral administration of ODTs taken without water than for CTs taken with water due to a delay in gastric emptying, the fluid shift in the donor chamber of the BE Checker without water was set longer than that taken with water. In the case of naftopidil ODTs and CTs, the values of the f2 function, representing the similarity of the permeation profiles, were 50 or higher when the fluid shift in ODTs taken without water was set at 1.5 or 2 times longer than that of the CTs taken with water. The values of the f2 function in permeation profiles of pitavastatin and memantine ODTs were both 62 when the optimized experimental settings for naftopidil formulations were applied. This methodology can be useful in formulation studies for estimating the BE probability between ODTs and CTs.

Harmonizing Biopredictive Methodologies Through the Product Quality Research Institute (PQRI) Part I: Biopredictive Dissolution of Ibuprofen and Dipyridamole Tablets

Assessing in vivo performance to inform formulation selection and development decisions is an important aspect of drug development. Biopredictive dissolution methodologies for oral dosage forms have been developed to understand in vivo performance, assist in formulation development/optimization, and forecast the outcome of bioequivalence studies by combining them with simulation tools to predict plasma profiles in humans. However, unlike compendial dissolution methodologies, the various biopredictive methodologies have not yet been harmonized or standardized. This manuscript presents the initial phases of an effort to develop best practices and move toward standardization of the biopredictive methodologies through the Product Quality Research Institute (PQRI, https://pqri.org ) entitled "The standardization of in vitro predictive dissolution methodologies and in silico bioequivalence study Working Group." This Working Group (WG) is comprised of participants from 10 pharmaceutical companies and academic institutes. The project will be accomplished in a total of five phases including assessing the performance of dissolution protocols designed by the individual WG members, and then building "best practice" protocols based on the initial dissolution profiles. After refining the "best practice" protocols to produce equivalent dissolution profiles, those will be combined with physiologically based biopharmaceutics models (PBBM) to predict plasma profiles. In this manuscript, the first two of the five phases are reported, namely generating biopredictive dissolution profiles for ibuprofen and dipyridamole and using those dissolution profiles with PBBM to match the clinical plasma profiles. Key experimental parameters are identified, and this knowledge will be applied to build the "best practice" protocol in the next phase.

Evaluation and prediction of oral drug absorption and bioequivalence with food-drug interaction

This article reviews the impacts on the in vivo prediction of oral bioavailability (BA) and bioequivalence (BE) based on Biopharmaceutical classification systems (BCS) by the food-drug interaction (food effect) and the gastrointestinal (GI) environmental change. Various in vitro and in silico predictive methodologies have been used to expect the BA and BE of the test oral formulation. Food intake changes the GI physiology and environment, which affect oral drug absorption and its BE evaluation. Even though the pHs and bile acids in the GI tract would have significant influence on drug dissolution and, hence, oral drug absorption, those impacts largely depend on the physicochemical properties of oral medicine, active pharmaceutical ingredients (APIs). BCS class I and III drugs are high soluble drugs in the physiological pH range, food-drug interaction may not affect their BA. On the other hand, BCS class II and IV drugs have pH-dependent solubility, and the more bile acid secretion and the pH changes by food intake might affect their BA. In this report, the GI physiological changes between the fasted and fed states are described and the prediction on the oral drug absorption by food-drug interaction have been introduced.

Lowly-buffered biorelevant dissolution testing is not necessarily biopredictive of human bioequivalence study outcome: Relationship between dissolution and pharmacokinetics

It has been revealed that buffer capacity of aspirated human intraluminal fluid is much lower than that of in vitro compendial dissolution media. Since buffer capacity significantly alters the dissolution profile of certain drug products, dissolution testing in highly buffered media dictates poor predictability of in vivo drug performance. To mitigate this inconsistency, low buffer capacity medium was suggested as an in vivo representation (biorelevant dissolution testing). The purpose of this study was to characterize the dissolution profiles of enteric-coated drug products in different buffer capacity media in a flow through cell dissolution apparatus, and to evaluate the in vivo predictability of human bioequivalence study outcomes conducted in the fasted state. It was confirmed that the lower the buffer capacity of dissolution media, the higher the discriminatory power of esomeprazole magnesium hydrate enteric-coated pellets, reflecting human bioequivalence failure. In the meantime, two duloxetine hydrochloride enteric-coated pellets also exhibited distinct dissolution profiles in such a lowly buffered medium despite the fact that these two are bioequivalent in human. Biopharmaceutical and pharmacokinetic characteristics comparison suggested that low intestinal permeability and small systemic elimination rate of duloxetine hinders the clear impact of different dissolution profile on its in vivo performance. These data suggest that dissolution comparison in physiologically-relevant low buffer capacity media is not always indicative of human bioequivalence. Instead, biopharmaceutical and pharmacokinetic aspects must be taken into consideration to make biorelevant dissolution testing biopredictive.

An In Vivo Predictive Dissolution Methodology (iPD Methodology) with a BCS Class IIb Drug Can Predict the In Vivo Bioequivalence Results: Etoricoxib Products

The purpose of this study was to predict in vivo performance of three oral products of Etoricoxib (Arcoxia^® as reference and two generic formulations in development) by conducting in vivo predictive dissolution with GIS (Gastro Intestinal Simulator) and computational analysis. Those predictions were compared with the results from previous bioequivalence (BE) human studies. Product dissolution studies were performed using a computer-controlled multicompartmental dissolution device (GIS) equipped with three dissolution chambers, representing stomach, duodenum, and jejunum, with integrated transit times and secretion rates. The measured dissolved amounts were modelled in each compartment with a set of differential equations representing transit, dissolution, and precipitation processes. The observed drug concentration by in vitro dissolution studies were directly convoluted with permeability and disposition parameters from literature to generate the predicted plasma concentrations. The GIS was able to detect the dissolution differences among reference and generic formulations in the gastric chamber where the drug solubility is high (pH 2) while the USP 2 standard dissolution test at pH 2 did not show any difference. Therefore, the current study confirms the importance of multicompartmental dissolution testing for weak bases as observed for other case examples but also the impact of excipients on duodenal and jejunal in vivo behavior.

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.

Evaluating supersaturation in vitro and predicting its performance in vivo with Biphasic gastrointestinal Simulator: A case study of a BCS IIB drug

This study aimed to develop an evaluation approach for supersaturation by employing an in vitro bio-mimicking apparatus designed to predict in vivo performance. The Biphasic Gastrointestinal Simulator (BGIS) is composed of three chambers with absorption phases that represent the stomach, duodenum, and jejunum, respectively. The concentration of apatinib in each chamber was detected by fiber optical probes in situ. The dissolution data and the pharmacokinetic data were correlated by Gastroplus^TM. The precipitates were characterized by polarizing microscope, Scanning Electron Microscopy, Powder X-ray diffraction and Differential scanning calorimetry. According to the results, Vinylpyrrolidone-vinyl acetate copolymer (CoPVP) prolonged supersaturation by improving solubility and inhibiting crystallization, while Hydroxypropyl methylcellulose (HPMC) prolonged supersaturation by inhibiting crystallization alone. Furthermore, a predictive in vitro-in vivo correlation was established, which confirmed the anti-precipitation effect of CoPVP and HPMC on in vitro performance and in vivo behavior. In conclusion, CoPVP and HPMC increased and prolonged the supersaturation of apatinib, and then improved its bioavailability. Moreover, BGIS was demonstrated to be a significant approach for simulating in vivo conditions for in vitro-in vivo correlation in a supersaturation study. This study presents a promising approach for evaluating supersaturation, screening precipitation inhibitors in vitro, and predicting their performances in vivo.

The Biopharmaceutics Classification System (BCS) and the Biopharmaceutics Drug Disposition Classification System (BDDCS): Beyond guidelines

The recent impact of the Biopharmaceutics Classification System (BCS) and the Biopharmaceutics Drug Disposition Classification System (BDDCS) on relevant scientific advancements is discussed. The major advances associated with the BCS concern the extensive work on dissolution of poorly absorbed BCS class II drugs in nutritional liquids (e.g. milk, peanut oil) and biorelevant media for the accurate prediction of the rate and the extent of oral absorption. The use of physiologically based pharmacokinetic (PBPK) modeling as predictive tool for bioavailability is also presented. Since recent dissolution studies demonstrate that the two mechanisms (diffusion- and reaction-limited dissolution) take place simultaneously, the neglected reaction-limited dissolution models are discussed, regarding the biopharmaceutical classification of drugs. Solubility- and dissolution-enhancing formulation strategies based on the supersaturation principle to enhance the extent of drug absorption, along with the applications of the BDDCS to the understanding of disposition phenomena are reviewed. Finally, recent classification systems relevant either to the BCS or the BDDCS are presented. These include: i) a model independent approach based on %metabolism and the fulfilment (or not) of the current regulatory dissolution criteria, ii) the so called ΑΒΓ system, a continuous version of the BCS, and iii) the so-called Extended Clearance Classification System (ECCS). ECCS uses clearance concepts (physicochemical properties and membrane permeability) to classify compounds and differentiates from BDDCS by bypassing the measure of solubility (based on the assumption that since it inter-correlates with lipophilicity, it is not directly relevant to clearance mechanisms or elimination).

Exploring Bioequivalence of Dexketoprofen Trometamol Drug Products with the Gastrointestinal Simulator (GIS) and Precipitation Pathways Analyses

The present work aimed to explain the differences in oral performance in fasted humans who were categorized into groups based on the three different drug product formulations of dexketoprofen trometamol (DKT) salt—Using a combination of in vitro techniques and pharmacokinetic analysis. The non-bioequivalence (non-BE) tablet group achieved higher plasma C_max and area under the curve (AUC) than the reference and BE tablets groups, with only one difference in tablet composition, which was the presence of calcium monohydrogen phosphate, an alkalinizing excipient, in the tablet core of the non-BE formulation. Concentration profiles determined using a gastrointestinal simulator (GIS) apparatus designed with 0.01 N hydrochloric acid and 34 mM sodium chloride as the gastric medium and fasted state simulated intestinal fluids (FaSSIF-v1) as the intestinal medium showed a faster rate and a higher extent of dissolution of the non-BE product compared to the BE and reference products. These in vitro profiles mirrored the fraction doses absorbed in vivo obtained from deconvoluted plasma concentration–time profiles. However, when sodium chloride was not included in the gastric medium and phosphate buffer without bile salts and phospholipids were used as the intestinal medium, the three products exhibited nearly identical concentration profiles. Microscopic examination of DKT salt dissolution in the gastric medium containing sodium chloride identified that when calcium phosphate was present, the DKT dissolved without conversion to the less soluble free acid, which was consistent with the higher drug exposure of the non-BE formulation. In the absence of calcium phosphate, however, dexketoprofen trometamol salt dissolution began with a nano-phase formation that grew to a liquid–liquid phase separation (LLPS) and formed the less soluble free acid crystals. This phenomenon was dependent on the salt/excipient concentrations and the presence of free acid crystals in the salt phase. This work demonstrated the importance of excipients and purity of salt phase on the evolution and rate of salt disproportionation pathways. Moreover, the presented data clearly showed the usefulness of the GIS apparatus as a discriminating tool that could highlight the differences in formulation behavior when utilizing physiologically-relevant media and experimental conditions in combination with microscopy imaging.

Innovation for Generic Drugs: Science and Research Under the Generic Drug User Fee Amendments of 2012

Regulatory science is science and research intended to improve decision making in a regulatory framework. Improvements in decision making can be in both accuracy (making better decisions) and in efficiency (making faster decisions). Science and research supported by the Generic Drug User Fee Amendments of 2012 (GDUFA) have focused on two innovative methodologies that work together to enable new approaches to development and review of generic drugs: quantitative models and advanced in vitro product characterization. Quantitative models faithfully represent current scientific understanding. They are tools pharmaceutical scientists and clinical pharmacologists use for making better and faster product development decisions. Advances in the in vitro product comparisons provide the measurements of product differences that are the critical input into the models. This paper outlines four areas where science and research funded by GDUFA support synergistic use of models and characterization at critical decision points during generic drug product development and review.

Linking the Gastrointestinal Behavior of Ibuprofen with the Systemic Exposure between and within Humans-Part 1: Fasted State Conditions

The goal of this project was to explore and to statistically evaluate the responsible gastrointestinal (GI) factors that are significant factors in explaining the systemic exposure of ibuprofen, between and within human subjects. In a previous study, we determined the solution and total concentrations of ibuprofen as a function of time in aspirated GI fluids, after oral administration of an 800 mg IR tablet (reference standard) of ibuprofen to 20 healthy volunteers in fasted state conditions. In addition, we determined luminal pH and motility pressure recordings that were simultaneously monitored along the GI tract. Blood samples were taken to determine ibuprofen plasma levels. In this work, an in-depth statistical and pharmacokinetic analysis was performed to explain which underlying GI variables are determining the systemic concentrations of ibuprofen between (inter-) and within (intra-) subjects. In addition, the obtained plasma profiles were deconvoluted to link the fraction absorbed with the fraction dissolved. Multiple linear regressions were performed to explain and quantitatively express the impact of underlying GI physiology on systemic exposure of the drug (in terms of plasma C_max/AUC and plasma T_max). The exploratory analysis of the correlation between plasma C_max/AUC and the time to the first phase III contractions postdose (TMMC-III) explains ∼40% of the variability in plasma C_max for all fasted state subjects. We have experimentally shown that the in vivo intestinal dissolution of ibuprofen is dependent upon physiological variables like, in this case, pH and postdose phase III contractions. For the first time, this work presents a thorough statistical analysis explaining how the GI behavior of an ionized drug can explain the systemic exposure of the drug based on the individual profiles of participating subjects. This creates a scientifically based and rational framework that emphasizes the importance of including pH and motility in a predictive in vivo dissolution methodology to forecast the in vivo performance of a drug product. Moreover, as no extensive first-pass metabolism is considered for ibuprofen, this study demonstrates how intraluminal drug behavior is reflecting the systemic exposure of a drug.

Formulation predictive dissolution (fPD) testing to advance oral drug product development: An introduction to the US FDA funded '21st Century BA/BE' project

Over the past decade, formulation predictive dissolution (fPD) testing has gained increasing attention. Another mindset is pushed forward where scientists in our field are more confident to explore the in vivo behavior of an oral drug product by performing predictive in vitro dissolution studies. Similarly, there is an increasing interest in the application of modern computational fluid dynamics (CFD) frameworks and high-performance computing platforms to study the local processes underlying absorption within the gastrointestinal (GI) tract. In that way, CFD and computing platforms both can inform future PBPK-based in silico frameworks and determine the GI-motility-driven hydrodynamic impacts that should be incorporated into in vitro dissolution methods for in vivo relevance. Current compendial dissolution methods are not always reliable to predict the in vivo behavior, especially not for biopharmaceutics classification system (BCS) class 2/4 compounds suffering from a low aqueous solubility. Developing a predictive dissolution test will be more reliable, cost-effective and less time-consuming as long as the predictive power of the test is sufficiently strong. There is a need to develop a biorelevant, predictive dissolution method that can be applied by pharmaceutical drug companies to facilitate marketing access for generic and novel drug products. In 2014, Prof. Gordon L. Amidon and his team initiated a far-ranging research program designed to integrate (1) in vivo studies in humans in order to further improve the understanding of the intraluminal processing of oral dosage forms and dissolved drug along the gastrointestinal (GI) tract, (2) advancement of in vitro methodologies that incorporates higher levels of in vivo relevance and (3) computational experiments to study the local processes underlying dissolution, transport and absorption within the intestines performed with a new unique CFD based framework. Of particular importance is revealing the physiological variables determining the variability in in vivo dissolution and GI absorption from person to person in order to address (potential) in vivo BE failures. This paper provides an introduction to this multidisciplinary project, informs the reader about current achievements and outlines future directions.

Evaluation and optimized selection of supersaturating drug delivery systems of posaconazole (BCS class 2b) in the gastrointestinal simulator (GIS): An in vitro-in silico-in vivo approach

Supersaturating drug delivery systems (SDDS) have been put forward in the recent decades in order to circumvent the issue of low aqueous solubility. Prior to the start of clinical trials, these enabling formulations should be adequately explored in in vitro/in silico studies in order to understand their in vivo performance and to select the most appropriate and effective formulation in terms of oral bioavailability and therapeutic outcome. The purpose of this work was to evaluate the in vivo performance of four different oral formulations of posaconazole (categorized as a biopharmaceutics classification system (BCS) class 2b compound) based on the in vitro concentrations in the gastrointestinal simulator (GIS), coupled with an in silico pharmacokinetic model to predict their systemic profiles. Recently published intraluminal and systemic concentrations of posaconazole for these formulations served as a reference to validate the in vitro and in silico results. Additionally, the morphology of the formed precipitate of posaconazole was visualized and characterized by optical microscopy studies and thermal analysis. This multidisciplinary work demonstrates an in vitro-in silico-in vivo approach that provides a scientific basis for screening SDDS by a user-friendly formulation predictive dissolution (fPD) device in order to rank these formulations towards their in vivo performance.

Population Balance Model for Simulation of the Supersaturation-Precipitation Behavior of Drugs in Supersaturable Solid Forms

We developed a simulation method to describe in vitro drug concentration-time profiles under supersaturated conditions. In a nonsink dissolution test of carbamazepine polymorphic form III (CBZ_III), a model supersaturable solid, the concentration of carbamazepine reached a supersaturated state against its dihydrate form (CBZ_DH). After a certain period, de-supersaturation due to the precipitation of CBZ_DH was observed. In the simulation of this typical dissolution-precipitation profile, the precipitation process of CBZ_DH was simulated by a population balance model in which the rates of primary/secondary nucleation and growth of CBZ_DH were considered. Six rate constants in the precipitation model were determined from de-supersaturation profiles in unseeded isothermal crystallization experiments of CBZ_DH. The dissolution process of CBZ_III was modeled on the basis of its dissolution profile under a sink condition. The simulated concentration versus time curves satisfactorily reproduced the characteristics of dissolution, supersaturation, and precipitation behavior of the model drug. The presented method will enable rational design of formulations and accurate prediction of the oral absorbability of drugs in supersaturable solid forms.