Biorelevant Media to Simulate Fluids in the Ascending Colon of Humans and Their Usefulness in Predicting Intracolonic Drug Solubility

Development of ion-triggered in situ gel containing ketoconazole/hydroxypropyl-β-cyclodextrin for ocular delivery: in vitro and in vivo evaluation

The application of ketoconazole (KET) in ocular drug delivery is restricted by its poor aqueous solubility though its broad-spectrum antifungal activity. The aim of this study is to develop an ion-sensitive in situ gel (ISG) of KET to promote its ocular bioavailability in topical application. The solubility of KET in water was increased by complexation with hydroxypropyl-β-cyclodextrin (HPβCD), then KET-HPβCD inclusion complex (KET-IC) was fabricated into an ion-sensitive ISG triggered by sodium alginate (SA). The in vitro drug release and antifungal activities investigations demonstrated that the KET-IC-ISG formulation increased drug release and anti-fungal activities compared to pure KET. The ex vivo rabbit corneal permeation studied demonstrated higher permeability of KET-IC-ISG formulation (Papp of (6.34 ± 0.21) × 10-4 cm/h) than pure KET (Papp of (3.09 ± 0.09) × 10-4 cm/h). The cytotoxicity assay and the ocular irritation study in rabbits confirmed the KET-IC-ISG safety and well tolerance. The ocular pharmacokinetics of KET in rabbits was investigated and the results showed that the KET-IC-ISG increased its bioavailability in cornea by 47-fold. In conclusion, the KET-IC-ISG system promoted the precorneal retention, the ocular drug bioavailability and the developed formulation is a potential strategy to treat mycotic keratitis.

Characterization of luminal contents from the fasted human proximal colon

To treat colonic diseases more effectively, improved therapies are urgently needed. In this respect, delivering drugs locally to the colon is a key strategy to achieve higher local drug concentrations while minimizing systemic side effects. Understanding the luminal environment is crucial to efficiently develop such targeted therapies and to predict drug disposition in the colon. In this clinical study, we collected colonic contents from an undisturbed fasted proximal colon via colonoscopy and characterized their composition with regard to drug disposition. Colonic pH, osmolality, protein content, bile salts, lipids, phospholipids and short-chain fatty acids were investigated in 10 healthy volunteers (8 male and 2 female, age 19-25). The unique environment of the proximal colon was reflected in the composition of the sampled luminal fluids and the effect of the microbiota could be observed on the pH (median 6.55), the composition of bile salts (majority deconjugated and secondary), and the abundance of short-chain fatty acids. At the same time, an increase in phospholipid concentration, osmolality and total protein content compared to reported ileal values was seen, likely resulting from desiccation. Lipids could only be found in low quantities and mainly in the form of cholesterol and free fatty acids, showing almost complete digestion and absorption by the time luminal contents reach the colon. All characteristics also displayed the considerable intersubject variability found in different regions of the gastrointestinal tract. This study contributes to an improved understanding of the luminal conditions in the proximal colon and facilitates the development of new predictive tools to study colonic drug absorption.

Poly(D,l-lactide-co-glycolide) particles are metabolised by the gut microbiome and elevate short chain fatty acids

The production of short chain fatty acids (SCFAs) by the colonic microbiome has numerous benefits for human health, including maintenance of epithelial barrier function, suppression of colitis, and protection against carcinogenesis. Despite the therapeutic potential, there is currently no optimal approach for elevating the colonic microbiome's synthesis of SCFAs. In this study, poly(D,l-lactide-co-glycolide) (PLGA) was investigated for this application, as it was hypothesised that the colonic microbiota would metabolise PLGA to its lactate monomers, which would promote the resident microbiota's synthesis of SCFAs. Two grades of spray dried PLGA, alongside a lactate bolus control, were screened in an advanced model of the human colon, known as the M-SHIME® system. Whilst the high molecular weight (Mw) grade of PLGA was stable in the presence of the microbiota sourced from three healthy humans, the low Mw PLGA (PLGA 2) was found to be metabolised. This microbial degradation led to sustained release of lactate over 48 h and increased concentrations of the SCFAs propionate and butyrate. Further, microbial synthesis of harmful ammonium was significantly reduced compared to untreated controls. Interestingly, both types of PLGA were found to influence the composition of the luminal and mucosal microbiota in a donor-specific manner. An in vitro model of an inflamed colonic epithelium also showed the polymer to affect the expression of pro- and anti-inflammatory markers, such as interleukins 8 and 10. The findings of this study reveal PLGA's sensitivity to enzymatic metabolism in the gut, which could be harnessed for therapeutic elevation of colonic SCFAs.

Thermodynamic solubility measurement without chemical analysis

In this work, the optical imaging based single particle analysis (SPA) and the gold standard shake-flask (SF) solubility methods are compared. We show that to analyze pharmaceutical compounds spanning 7 log units in solubility and a diverse chemical space with limited resources, several analytical techniques are required (HPLC-UV, LC-MS, refractometry and UV-Vis spectrometry), whereas solely the SPA method is able to analyze all the same compounds. SPA experiments take only minutes, while for SF, it may take days to reach thermodynamic equilibration. This decreases the time span needed for the solubility experiment from initial preparations to obtaining the result from roughly three days to less than three hours. The optimal particle size for SPA ranges from approximately one to hundreds of microns. Challenges include measuring large particles, very fast dissolving compounds and handling small sample sizes. Inherent exclusion of density from the SPA measurement is a potential source of error for compounds with very low or high density values. The average relative difference of 37 % between the two methods is very good in the realm of solubility, where 400 % interlaboratory reproducibility can be expected.

Physiologically Based Biopharmaceutics Modeling of regional and colon absorption in humans

Colon absorption is a key determinant for successful development of extended release and colon targeted drug products. This is the first systematic evaluation of the ability to predict in vivo regional differences in absorption and the extent of colon absorption in humans using mechanistic physiologically based biopharmaceutics modeling (PBBM). A new dataset, consisting of 19 drugs with a wide range of biopharmaceutics properties and extent of colon absorption in humans, was established. Mechanistic predictions of the extent of absorption and plasma exposure after oral, or jejunal and direct colon administration were performed in GastroPlus and GI-Sim using an a priori approach. Two new colon models developed in GI-Sim, were also evaluated to assess if the prediction performance could be improved. Both GastroPlus and GI-Sim met the pre-defined criteria for accurate predictions of regional and colon absorption for high permeability drugs irrespective of formulation type, while the prediction performance was poor for low permeability drugs. For solutions, the two new GI-Sim colon models improved the colon absorption prediction performance for the low permeability drugs while maintaining the accurate prediction performance for the high permeability drugs. In contrast, the prediction performance decreased for non-solutions using the two new colon models. In conclusion, PBBM can be used with sufficient accuracy to predict regional and colon absorption in humans for high permeability drugs in candidate selection as well as early design and development of extended release or colon targeted drug products. The prediction performance of the current models needs to be improved to allow high accuracy predictions for commercial drug product applications including highly accurate predictions of the entire plasma concentration-time profiles as well as for low permeability drugs.

Use of In Vitro Dynamic Colon Model (DCM) to Inform a Physiologically Based Biopharmaceutic Model (PBBM) to Predict the In Vivo Performance of a Modified-Release Formulation of Theophylline

A physiologically based biopharmaceutic model (PBBM) of a modified-release formulation of theophylline (Uniphyllin Continus® 200 mg tablet) was developed and implemented to predict the pharmacokinetic (PK) data of healthy male volunteers by integrating dissolution profiles measured in a biorelevant in vitro model: the Dynamic Colon Model (DCM). The superiority of the DCM over the United States Pharmacopeia (USP) Apparatus II (USP II) was demonstrated by the superior predictions for the 200 mg tablet (average absolute fold error (AAFE): 1.1-1.3 (DCM) vs. 1.3-1.5 (USP II). The best predictions were obtained using the three motility patterns (antegrade and retrograde propagating waves, baseline) in the DCM, which produced similar PK profiles. However, extensive erosion of the tablet occurred at all agitation speeds used in USP II (25, 50 and 100 rpm), resulting in an increased drug release rate in vitro and overpredicted PK data. The PK data of the Uniphyllin Continus® 400 mg tablet could not be predicted with the same accuracy using dissolution profiles from the DCM, which might be explained by differences in upper gastrointestinal (GI) tract residence times between the 200 and 400 mg tablets. Thus, it is recommended that the DCM be used for dosage forms in which the main release phenomena take place in the distal GI tract. However, the DCM again showed a better performance based on the overall AAFE compared to the USP II. Regional dissolution profiles within the DCM cannot currently be integrated into Simcyp®, which might limit the predictivity of the DCM. Thus, further compartmentalization of the colon within PBBM platforms is required to account for observed intra-regional differences in drug distribution.

Supersaturation and Precipitation Applicated in Drug Delivery Systems: Development Strategies and Evaluation Approaches

Supersaturation is a promising strategy to improve gastrointestinal absorption of poorly water-soluble drugs. Supersaturation is a metastable state and therefore dissolved drugs often quickly precipitate again. Precipitation inhibitors can prolong the metastable state. Supersaturating drug delivery systems (SDDS) are commonly formulated with precipitation inhibitors, hence the supersaturation is effectively prolonged for absorption, leading to improved bioavailability. This review summarizes the theory of and systemic insight into supersaturation, with the emphasis on biopharmaceutical aspects. Supersaturation research has developed from the generation of supersaturation (pH-shift, prodrug and SDDS) and the inhibition of precipitation (the mechanism of precipitation, the character of precipitation inhibitors and screening precipitation inhibitors). Then, the evaluation approaches to SDDS are discussed, including in vitro, in vivo and in silico studies and in vitro-in vivo correlations. In vitro aspects involve biorelevant medium, biomimetic apparatus and characterization instruments; in vivo aspects involve oral absorption, intestinal perfusion and intestinal content aspiration and in silico aspects involve molecular dynamics simulation and pharmacokinetic simulation. More physiological data of in vitro studies should be taken into account to simulate the in vivo environment. The supersaturation theory should be further completed, especially with regard to physiological conditions.

Colonic drug delivery: Formulating the next generation of colon-targeted therapeutics

Colonic drug delivery can facilitate access to unique therapeutic targets and has the potential to enhance drug bioavailability whilst reducing off-target effects. Delivering drugs to the colon requires considered formulation development, as both oral and rectal dosage forms can encounter challenges if the colon's distinct physiological environment is not appreciated. As the therapeutic opportunities surrounding colonic drug delivery multiply, the success of novel pharmaceuticals lies in their design. This review provides a modern insight into the key parameters determining the effective design and development of colon-targeted medicines. Influential physiological features governing the release, dissolution, stability, and absorption of drugs in the colon are first discussed, followed by an overview of the most reliable colon-targeted formulation strategies. Finally, the most appropriate in vitro, in vivo, and in silico preclinical investigations are presented, with the goal of inspiring strategic development of new colon-targeted therapeutics.

Single domain antibodies against enteric pathogen virulence factors are active as curli fiber fusions on probiotic E. coli Nissle 1917

Enteric microbial pathogens, including Escherichia coli, Shigella and Cryptosporidium species, take a particularly heavy toll in low-income countries and are highly associated with infant mortality. We describe here a means to display anti-infective agents on the surface of a probiotic bacterium. Because of their stability and versatility, VHHs, the variable domains of camelid heavy-chain-only antibodies, have potential as components of novel agents to treat or prevent enteric infectious disease. We isolated and characterized VHHs targeting several enteropathogenic E. coli (EPEC) virulence factors: flagellin (Fla), which is required for bacterial motility and promotes colonization; both intimin and the translocated intimin receptor (Tir), which together play key roles in attachment to enterocytes; and E. coli secreted protein A (EspA), an essential component of the type III secretion system (T3SS) that is required for virulence. Several VHHs that recognize Fla, intimin, or Tir blocked function in vitro. The probiotic strain E. coli Nissle 1917 (EcN) produces on the bacterial surface curli fibers, which are the major proteinaceous component of E. coli biofilms. A subset of Fla-, intimin-, or Tir-binding VHHs, as well as VHHs that recognize either a T3SS of another important bacterial pathogen (Shigella flexneri), a soluble bacterial toxin (Shiga toxin or Clostridioides difficile toxin TcdA), or a major surface antigen of an important eukaryotic pathogen (Cryptosporidium parvum) were fused to CsgA, the major curli fiber subunit. Scanning electron micrographs indicated CsgA-VHH fusions were assembled into curli fibers on the EcN surface, and Congo Red binding indicated that these recombinant curli fibers were produced at high levels. Ectopic production of these VHHs conferred on EcN the cognate binding activity and, in the case of anti-Shiga toxin, was neutralizing. Taken together, these results demonstrate the potential of the curli-based pathogen sequestration strategy described herein and contribute to the development of novel VHH-based gut therapeutics.

In Vitro Methodologies for Evaluating Colon-Targeted Pharmaceutical Products and Industry Perspectives for Their Applications

Several locally acting colon-targeted products to treat colonic diseases have been recently developed and marketed, taking advantage of gastrointestinal physiology to target delivery. Main mechanisms involve pH-dependent, time-controlled and/or enzymatic-triggered release. With site of action located before systemic circulation and troublesome colonic sampling, there is room for the introduction of meaningful in vitro methods for development, quality control (QC) and regulatory applications of these formulations. A one-size-fits-all method seems unrealistic, as the selection of experimental conditions should resemble the physiological features exploited to trigger the release. This article reviews the state of the art for bio-predictive dissolution testing of colon-targeted products. Compendial methods overlook physiological aspects, such as buffer molarity and fluid composition. These are critical for pH-dependent products and time-controlled systems containing ionizable drugs. Moreover, meaningful methods for enzymatic-triggered products including either bacteria or enzymes are completely ignored by pharmacopeias. Bio-predictive testing may accelerate the development of successful products, although this may require complex methodologies. However, for high-throughput routine testing (e.g., QC), simplified methods can be used where balance is struck between simplicity, robustness and transferability on one side and bio-predictivity on the other. Ultimately, bio-predictive methods can occupy a special niche in terms of supplementing plasma concentration data for regulatory approval.

Dissolution Challenges Associated with the Surface pH of Drug Particles: Integration into Mechanistic Oral Absorption Modeling

The present work aimed to differentiate between in vitro dissolution profiles of ibuprofen as input for GastroPlus™ and to see the impact on systemic exposure. In vitro dissolution profiles of ibuprofen obtained under low- and high-buffered dissolution media were used as input using the z-factor approach. In a second step, a customized surface pH calculator was applied to predict the surface pH of ibuprofen under these low- and high-buffered dissolution conditions. These surface pH values were adopted in GastroPlus™ and simulations were performed to predict the systemic outcome. Simulated data were compared with systemic data of ibuprofen obtained under fasted state conditions in healthy subjects. The slower dissolution rate observed when working under low-buffered conditions nicely matched with the slower dissolution rate as observed during the clinical aspiration study and was in line with the systemic exposure of the drug. Finally, a population simulation was performed to explore the impact of z-factor towards bioequivalence (BE) criteria (so-called safe space). Concerning future perspectives, the customized calculator should be developed in such a way to make it possible to predict the dissolution rate (being informed by the particle size distribution) which, in its turn, can be used as a surrogate to predict the USP2 dissolution curve. Subsequently, validation can be done by using this profile as input for PBPK platforms.

Integration of advanced methods and models to study drug absorption and related processes: An UNGAP perspective

This collection of contributions from the European Network on Understanding Gastrointestinal Absorption-related Processes (UNGAP) community assembly aims to provide information on some of the current and newer methods employed to study the behaviour of medicines. It is the product of interactions in the immediate pre-Covid period when UNGAP members were able to meet and set up workshops and to discuss progress across the disciplines. UNGAP activities are divided into work packages that cover special treatment populations, absorption processes in different regions of the gut, the development of advanced formulations and the integration of food and pharmaceutical scientists in the food-drug interface. This involves both new and established technical approaches in which we have attempted to define best practice and highlight areas where further research is needed. Over the last months we have been able to reflect on some of the key innovative approaches which we were tasked with mapping, including theoretical, in silico, in vitro, in vivo and ex vivo, preclinical and clinical approaches. This is the product of some of us in a snapshot of where UNGAP has travelled and what aspects of innovative technologies are important. It is not a comprehensive review of all methods used in research to study drug dissolution and absorption, but provides an ample panorama of current and advanced methods generally and potentially useful in this area. This collection starts from a consideration of advances in a priori approaches: an understanding of the molecular properties of the compound to predict biological characteristics relevant to absorption. The next four sections discuss a major activity in the UNGAP initiative, the pursuit of more representative conditions to study lumenal dissolution of drug formulations developed independently by academic teams. They are important because they illustrate examples of in vitro simulation systems that have begun to provide a useful understanding of formulation behaviour in the upper GI tract for industry. The Leuven team highlights the importance of the physiology of the digestive tract, as they describe the relevance of gastric and intestinal fluids on the behaviour of drugs along the tract. This provides the introduction to microdosing as an early tool to study drug disposition. Microdosing in oncology is starting to use gamma-emitting tracers, which provides a link through SPECT to the next section on nuclear medicine. The last two papers link the modelling approaches used by the pharmaceutical industry, in silico to Pop-PK linking to Darwich and Aarons, who provide discussion on pharmacometric modelling, completing the loop of molecule to man.

In vitro models to evaluate ingestible devices: Present status and current trends

Orally ingestible medical devices offer significant opportunity in the diagnosis and treatment of gastrointestinal conditions. Their development necessitates the use of models that simulate the gastrointestinal environment on both a macro and micro scale. An evolution in scientific technology has enabled a wide range of in vitro, ex vivo and in vivo models to be developed that replicate the gastrointestinal tract. This review describes the landscape of the existing range of in vitro tools that are available to characterize ingestible devices. Models are presented with details on their benefits and limitations with regards to the evaluation of ingestible devices and examples of their use in the evaluation of such devices is presented where available. The multitude of models available provides a suite of tools that can be used in the evaluation of ingestible devices that should be selected on the functionality of the device and the mechanism of its function.

Quantification of Fluid Volume and Distribution in the Paediatric Colon via Magnetic Resonance Imaging

Previous studies have used magnetic resonance imaging (MRI) to quantify the fluid in the stomach and small intestine of children, and the stomach, small intestine and colon of adults. This is the first study to quantify fluid volumes and distribution using MRI in the paediatric colon. MRI datasets from 28 fasted (aged 0-15 years) and 18 fluid-fed (aged 10-16 years) paediatric participants were acquired during routine clinical care. A series of 2D- and 3D-based software protocols were used to measure colonic fluid volume and localisation. The paediatric colon contained a mean volume of 22.5 mL ± 41.3 mL fluid, (range 0-167.5 mL, median volume 0.80 mL) in 15.5 ± 17.5 discreet fluid pockets (median 12). The proportion of the fluid pockets larger than 1 mL was 9.6%, which contributed to 94.5% of the total fluid volume observed. No correlation was detected between all-ages and colonic fluid volume, nor was a difference in colonic fluid volumes observed based on sex, fed state or age group based on ICH-classifications. This study quantified fluid volumes within the paediatric colon, and these data will aid and accelerate the development of biorelevant tools to progress paediatric drug development for colon-targeting formulations.

UNGAP best practice for improving solubility data quality of orally administered drugs

An important goal of the European Cooperation in Science and Technology (COST) Action UNGAP (UNderstanding Gastrointestinal Absorption-related Processes, www.ungap.eu) is to improve standardization of methods relating to the study of oral drug absorption. Solubility is a general term that refers to the maximum achievable concentration of a compound dissolved in a liquid medium. For orally administered drugs, relevant information on drug properties is crucial during drug (product) development and at the regulatory level. Collection of reliable and reproducible solubility data requires careful application and understanding of the limitations of the selected experimental method. In addition, the purity of a compound and its solid state form, as well as experimental parameters such as temperature of experimentation, media related factors, and sample handling procedures can affect data quality. In this paper, an international consensus developed by the COST UNGAP network on recommendations for collecting high quality solubility data for the development of orally administered drugs is proposed.

Current challenges and future perspectives in oral absorption research: An opinion of the UNGAP network

Although oral drug delivery is the preferred administration route and has been used for centuries, modern drug discovery and development pipelines challenge conventional formulation approaches and highlight the insufficient mechanistic understanding of processes critical to oral drug absorption. This review presents the opinion of UNGAP scientists on four key themes across the oral absorption landscape: (1) specific patient populations, (2) regional differences in the gastrointestinal tract, (3) advanced formulations and (4) food-drug interactions. The differences of oral absorption in pediatric and geriatric populations, the specific issues in colonic absorption, the formulation approaches for poorly water-soluble (small molecules) and poorly permeable (peptides, RNA etc.) drugs, as well as the vast realm of food effects, are some of the topics discussed in detail. The identified controversies and gaps in the current understanding of gastrointestinal absorption-related processes are used to create a roadmap for the future of oral drug absorption research.

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.

Physiologically Based Biopharmaceutics Modeling of Regional and Colon Absorption in Dogs

Colon absorption is a key determinant for the successful development of modified-release (MR) formulations, and the risk that colon absorption may limit the in vivo performance of an MR product can be assessed early by various in vitro tests or by preclinical in vivo regional absorption studies in dogs. Mechanistic physiologically based biopharmaceutics modeling (PBBM) is becoming increasingly accepted to predict in vivo performance and guide formulation development; however, no evaluation of the ability to predict colon absorption has been performed. The purpose of this study was to investigate if regional and colon absorption of drugs in dogs could be predicted with sufficient accuracy using PBBM to enable the replacement of in vivo dog studies in the early assessment of colon absorption limitation risks. This was done by predicting the regional and colon absorption and plasma exposure of 14 drugs after administration to the dog colon according to an a priori approach using the in silico absorption models GI-Sim and GastroPlus. Predictive performance was primarily assessed by comparing observed and predicted plasma concentration-time profiles, AUC_0-t, and the relative bioavailability in the colon (F_rel,colon) as compared to an oral/duodenal reference. Trends in dependency of prediction performance on predicted fraction absorbed, permeability, and solubility/dissolution rate were also investigated. For GI-Sim, the absolute average fold error (AAFE) values for AUC_0-t and F_rel,colon were within a 2-fold prediction error for both solutions (1.88 and 1.51, respectively) and suspensions (1.58 and 1.99, respectively). For GastroPlus, the AAFE values for AUC_0-t and F_rel,colon were outside the set 2-fold prediction error limit for accurate predictions for both solutions (3.63 and 2.98, respectively) and suspensions (2.94 and 2.09, respectively). No trends for over- or underprediction were observed for GI-Sim, whereas GastroPlus showed a slight trend for underprediction of both AUC_0-t and F_rel,colon for compounds with low permeability. In addition, regional differences in the plasma profiles were qualitatively predicted in the majority of cases for both software. Despite the differences in prediction performance, both models can be considered to predict regional differences in absorption as well as AUC_0-t and F_rel,colon with acceptable accuracy in an early development setting. The results of this study indicate that it is acceptable to replace in vivo regional absorption studies in dogs with the evaluated models as a method for the early assessment of the risk for colon absorption limitation of MR drug product candidates.

Predicting budesonide performance in healthy subjects and patients with Crohn's disease using biorelevant in vitro dissolution testing and PBPK modeling

OBJECTIVES

Drug product performance might be affected in Crohn's disease (CD) patients compared to healthy subjects due to pathophysiological changes. Since a low number of clinical studies is performed in this patient population, physiologically-based pharmacokinetic (PBPK) models with integrated results from biorelevant in vitro dissolution studies could be used to assess differences in the bioavailability of drugs. Using this approach, budesonide was used as model drug and its performance in healthy subjects and CD patients was predicted and compared against observed pharmacokinetic data. The in vitro release tests, under healthy versus CD conditions, revealed a similar extent of drug release from a controlled-release budesonide formulation in the fasted state, whereas in the fed state a lower extent was observed with CD. Differences in the physiology of CD patients were identified in literature and their impact on budesonide performance was investigated with a PBPK model, revealing the highest impact on the simulated bioavailability for the reduced hepatic CYP3A4 enzyme abundance and lower human serum albumin concentration. For CD patients, a higher budesonide exposure compared to healthy subjects was predicted with a PBPK population adapted to CD physiology and in agreement with observed pharmacokinetic data. Budesonide performance in the fasted and fed state was successfully predicted in healthy subjects and CD patients using PBPK modeling and in vitro release testing. Following this approach, predictions of the direction and magnitude of changes in bioavailability due to CD could be made for other drugs and guide prescribers to adjust dosage regimens for CD patients accordingly.

Sporopollenin Exine Microcapsules as Potential Intestinal Delivery System of Probiotics

Despite several decades of research into encapsulation of bacteria, most of the proposed technologies are in the form of immobilized cultures. In this work, sporopollenin exine capsules (SECs) opened, using silica particles which act as pressing micro-probes, and loaded with Lactobacillus casei (L. casei) cells, are described for the first time. The proposed encapsulation provided ≈30× higher encapsulation yield (30.87%), compared to direct compression of SECs (0.99%). Encapsulated L. casei cells show 1.21- and 2.25-folds higher viability compared to free cells, in in vitro simulated fasted and fed media representing the human gastrointestinal (GI) tract, respectively. Encapsulated L. casei can proliferate inside the SECs, generating enough pressure to cause the SECs to burst and release the viable and metabolically active cells. The noticeable difference with the application of the SECs as a means of encapsulation is that the SECs may act as a bioreactor and provide time for the encapsulated cells to multiply thousands of times before being released, following the SEC's burst. The unique advantages of SECs alongside the proposed encapsulation method, demonstrates the potential application of SECs as delivery system of probiotics to the distal part of the human GI tract.

Drug Disposition in the Lower Gastrointestinal Tract: Targeting and Monitoring

The increasing prevalence of colonic diseases calls for a better understanding of the various colonic drug absorption barriers of colon-targeted formulations, and for reliable in vitro tools that accurately predict local drug disposition. In vivo relevant incubation conditions have been shown to better capture the composition of the limited colonic fluid and have resulted in relevant degradation and dissolution kinetics of drugs and formulations. Furthermore, drug hurdles such as efflux transporters and metabolising enzymes, and the presence of mucus and microbiome are slowly integrated into drug stability- and permeation assays. Traditionally, the well characterized Caco-2 cell line and the Ussing chamber technique are used to assess the absorption characteristics of small drug molecules. Recently, various stem cell-derived intestinal systems have emerged, closely mimicking epithelial physiology. Models that can assess microbiome-mediated drug metabolism or enable coculturing of gut microbiome with epithelial cells are also increasingly explored. Here we provide a comprehensive overview of the colonic physiology in relation to drug absorption, and review colon-targeting formulation strategies and in vitro tools to characterize colonic drug disposition.

Physiologically Based Pharmacokinetic/Pharmacodynamic Modeling to Support Waivers of In Vivo Clinical Studies: Current Status, Challenges, and Opportunities

Physiologically based pharmacokinetic/pharmacodynamic (PBPK/PD) modeling has been extensively applied to quantitatively translate in vitro data, predict the in vivo performance, and ultimately support waivers of in vivo clinical studies. In the area of biopharmaceutics and within the context of model-informed drug discovery and development (MID3), there is a rapidly growing interest in applying verified and validated mechanistic PBPK models to waive in vivo clinical studies. However, the regulatory acceptance of PBPK analyses for biopharmaceutics and oral drug absorption applications, which is also referred to variously as "PBPK absorption modeling" [Zhang et al. CPT: Pharmacometrics Syst. Pharmacol. 2017, 6, 492], "physiologically based absorption modeling", or "physiologically based biopharmaceutics modeling" (PBBM), remains rather low [Kesisoglou et al. J. Pharm. Sci. 2016, 105, 2723] [Heimbach et al. AAPS J. 2019, 21, 29]. Despite considerable progress in the understanding of gastrointestinal (GI) physiology, in vitro biopharmaceutic and in silico tools, PBPK models for oral absorption often suffer from an incomplete understanding of the physiology, overparameterization, and insufficient model validation and/or platform verification, all of which can represent limitations to their translatability and predictive performance. The complex interactions of drug substances and (bioenabling) formulations with the highly dynamic and heterogeneous environment of the GI tract in different age, ethnic, and genetic groups as well as disease states have not been yet fully elucidated, and they deserve further research. Along with advancements in the understanding of GI physiology and refinement of current or development of fully mechanistic in silico tools, we strongly believe that harmonization, interdisciplinary interaction, and enhancement of the translational link between in vitro, in silico, and in vivo will determine the future of PBBM. This Perspective provides an overview of the current status of PBBM, reflects on challenges and knowledge gaps, and discusses future opportunities around PBPK/PD models for oral absorption of small and large molecules to waive in vivo clinical studies.

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.

Salcaprozate sodium (SNAC) enhances permeability of octreotide across isolated rat and human intestinal epithelial mucosae in Ussing chambers

Octreotide is approved as a one-month injectable for treatment of acromegaly and neuroendocrine tumours. Oral delivery of the octapeptide is a challenge due mainly to low intestinal epithelial permeability. The intestinal permeation enhancer (PE) salcaprozate sodium (SNAC) has Generally Regarded As Safe (GRAS) status and is a component of an approved oral peptide formulation. The purpose of the study was to examine the capacity of salcaprozate sodium (SNAC), to increase its permeability across isolated rat intestinal mucosae from five regions and across human colonic mucosae mounted in Ussing chambers. Apical-side buffers were Kreb's-Henseleit (KH), fasted simulated intestinal fluid (FaSSIF-V2), rat simulated intestinal fluid (rSIF), and colonic simulated intestinal fluid (FaSSCoF). The basal apparent permeability coefficient (P_app) of [³H]-octreotide was equally low across rat intestinal regional mucosae in KH, rSIF, and FaSSIF-V2. Apical addition of 20 mM SNAC increased the P_app across rat tissue in KH: colon (by 3.2-fold) > ileum (3.4-fold) > upper jejunum (2.3-fold) > duodenum (1.4-fold) > stomach (1.4-fold). 20 mM and 40 mM SNAC also increased the P_app by 1.5-fold and 2.1-fold respectively across human colonic mucosae in KH. Transepithelial electrical resistance (TEER) values were reduced in the presence in SNAC especially in colonic regions. LC-MS/MS analysis of permeated unlabelled octreotide across human colonic mucosae in the presence of SNAC indicated that [³H]-octreotide remained intact. No gross damage was caused to rat or human mucosae by SNAC. Attenuation of the effects of SNAC was seen in rat jejunal mucosae incubated with FaSSIF-V2 and rSIF, and also to some extent in human colonic mucosae using FaSSCoF, suggesting interaction between SNAC with buffer components. In conclusion, SNAC showed potential as an intestinal permeation enhancer for octreotide, but in vivo efficacy may be attenuated by interactions with GI luminal fluid contents.

Gastrointestinal diseases and their impact on drug solubility: Crohn's disease

In order to investigate differences in drug solubilisation and dissolution in luminal fluids of Crohn's disease (CD) patients and healthy subjects, biorelevant media representative of CD patients were developed using information from literature and a Design of Experiment (DoE) approach. The CD media were characterised in terms of surface tension, osmolality, dynamic viscosity and buffer capacity and compared to healthy biorelevant media. To identify which drug characteristics are likely to present a high risk of altered drug solubility in CD, the solubility of six drugs was assessed in CD media and solubility differences were related to drug properties. Identified differences in CD patients compared to healthy subjects were a reduced concentration of bile salts, a higher gastric pH and a higher colonic osmolality. Differences in the properties of CD compared to healthy biorelevant media were mainly observed for surface tension and osmolality. Drug solubility of ionisable compounds was altered in gastric CD media compared to healthy biorelevant media. For drugs with moderate to high lipophilicity, a high risk of altered drug solubilisation in CD is expected, since a significant negative effect of log P and a positive effect of bile salts on drug solubility in colonic and fasted state intestinal CD media was observed. Simulating the conditions in CD patients in vitro offers the possibility to identify relevant differences in drug solubilisation without conducting expensive clinical trials.

Gastrointestinal diseases and their impact on drug solubility: Ulcerative Colitis

For poorly soluble compounds, drug product performance in patients with Ulcerative Colitis (UC) compared to healthy subjects can be affected due to differences in drug solubility in GI fluids. A risk assessment tool was developed to identify compounds with a high risk of altered solubility in the GI fluids of UC patients. Pathophysiological changes impacting on the composition of GI fluids in UC patients were considered and UC biorelevant media representative of the stomach, intestine and colon were developed based on biorelevant media based on healthy subjects and literature data using a Design of Experiment approach. The UC media were characterised and revealed differences in surface tension, osmolality and buffer capacity compared to media based on healthy subjects. The solubility of six drugs was investigated in UC biorelevant media and results were related to media- and drug-dependent factors. A lower drug solubility in UC intestinal media was observed for compounds with a high lipophilicity. In UC simulated colonic fluids, drug solubility was altered for ionisable compounds. Additionally, a higher solubility of neutral lipophilic drugs was observed in UC fasted state colonic media with increased concentrations of soluble proteins. The developed UC biorelevant media offer the possibility to identify the risk of altered drug solubilisation in UC patients without conducting expensive clinical trials. A high risk was related to drug ionization properties and lipophilicity in the current study with all investigated drugs showing differences in solubility in biorelevant media based on UC patients compared to healthy subjects.

Interpolymer Complexes of Eudragit® Copolymers as Novel Carriers for Colon-Specific Drug Delivery

Interpolymer complexes (IPC) based on Eudragit^® EPO and Eudragit^® S100 were investigated as potential carriers for oral controlled drug delivery to the colon. IPC samples were prepared by mixing copolymer solutions in organic solvents (ethanol, isopropanol:acetone mixture (60:40, % v/v) and tetrahydrofuran). According to the data of elemental analysis, FTIR-spectroscopy, X-ray photoelectron spectroscopy and thermal analysis these IPCs have excess of anionic copolymer (Eudragit^® S100) in their structure; they are stabilized by hydrogen and ionic intermacromolecular bonds and do not include free copolymer domains. IPC have pH-independent swelling properties in the media mimicking gastrointestinal tract (GIT) conditions and provide colon-specific delivery of indomethacin in buffer solutions (pH 1.2; 5.8; 6.8; 7.4) and in biorelevant media (fasted state simulated gastric fluid, fasted state simulated intestinal fluid—version 2 and fasted stated simulated colonic fluid).

Selection of In Vivo Predictive Dissolution Media Using Drug Substance and Physiological Properties

The rate and extent of drug dissolution in the gastrointestinal (GI) tract are highly dependent upon drug physicochemical properties and GI fluid properties. Biorelevant dissolution media (BDM), which aim to facilitate in vitro prediction of in vivo dissolution performance, have evolved with our understanding of GI physiology. However, BDM with a variety of properties and compositions are available, making the choice of dissolution medium challenging. In this tutorial, we describe a simple and quantitative methodology for selecting practical, yet physiologically relevant BDM representative of fasted humans for evaluating dissolution of immediate release formulations. Specifically, this methodology describes selection of pH, buffer species, and concentration and evaluates the importance of including bile salts and phospholipids in the BDM based upon drug substance log D, pK_a, and intrinsic solubility. The methodology is based upon a mechanistic understanding of how three main factors affect dissolution, including (1) drug ionization at gastrointestinal pH, (2) alteration of surface pH by charged drug species, and (3) drug solubilization in mixed lipidic aggregates comprising bile salts and phospholipids. Assessment of this methodology through testing and comparison with literature reports showed that the recommendations correctly identified when a biorelevant buffer capacity or the addition of bile salts and phospholipids to the medium would appreciably change the drug dissolution profile. This methodology can enable informed decisions about when a time, complexity, and/or cost-saving buffer is expected to lead to physiologically meaningful in vitro dissolution testing, versus when a more complex buffer would be required.

Biorelevant release testing of biodegradable microspheres intended for intra-articular administration

Characterization of controlled release formulations used for intra-articular (IA) drug administration is challenging. Bio-relevant synovial fluids (BSF), containing physiologically relevant amounts of hyaluronic acid, phospholipids and proteins, were recently proposed to simulate healthy and osteoarthritic conditions. This work aims to evaluate the performance of different controlled release formulations of methylprednisolone (MP) for IA administration, under healthy and disease states simulated conditions. Microspheres differed in grade of poly(lactide-co-glycolide) and in the theoretical drug content (i.e. 23 or 30% w/w). Their performance was compared with the commercially available suspension of MP acetate (MPA). Under osteoarthritic state simulated condition, proteins increased the MPA release and reduced the MPA hydrolysis rate, over 48 h. Regarding microspheres, the release patterns over 40 days were significantly influenced by the composition of BSF. The pattern of the release mechanism and the amount released was affected by the presence of proteins. Protein concentration affected the release and the concentration used is critical, particularly given the relevance of the concentrations to target patient populations, i.e. patients with osteoarthritis.

Local delivery of macromolecules to treat diseases associated with the colon

Current treatments for intestinal diseases including inflammatory bowel diseases, irritable bowel syndrome, and colonic bacterial infections are typically small molecule oral dosage forms designed for systemic delivery. The intestinal permeability hurdle to achieve systemic delivery from oral formulations of macromolecules is challenging, but this drawback can be advantageous if an intestinal region is associated with the disease. There are some promising formulation approaches to release peptides, proteins, antibodies, antisense oligonucleotides, RNA, and probiotics in the colon to enable local delivery and efficacy. We briefly review colonic physiology in relation to the main colon-associated diseases (inflammatory bowel disease, irritable bowel syndrome, infection, and colorectal cancer), along with the impact of colon physiology on dosage form design of macromolecules. We then assess formulation strategies designed to achieve colonic delivery of small molecules and concluded that they can also be applied some extent to macromolecules. We describe examples of formulation strategies in preclinical research aimed at colonic delivery of macromolecules to achieve high local concentration in the lumen, epithelial-, or sub-epithelial tissue, depending on the target, but with the benefit of reduced systemic exposure and toxicity. Finally, the industrial challenges in developing macromolecule formulations for colon-associated diseases are presented, along with a framework for selecting appropriate delivery technologies.

Comparing human peritoneal fluid and phosphate-buffered saline for drug delivery: do we need bio-relevant media?

An understanding of biological fluids at the site of administration is important to predict the fate of drug delivery systems in vivo. Little is known about peritoneal fluid; therefore, we have investigated this biological fluid and compared it to phosphate-buffered saline, a synthetic media commonly used for in vitro evaluation of intraperitoneal drug delivery systems. Human peritoneal fluid samples were analysed for electrolyte, protein and lipid levels. In addition, physicochemical properties were measured alongside rheological parameters. Significant inter-patient variations were observed with regard to pH (p < 0.001), buffer capacity (p < 0.05), osmolality (p < 0.001) and surface tension (p < 0.05). All the investigated physicochemical properties of peritoneal fluid differed from phosphate-buffered saline (p < 0.001). Rheological examination of peritoneal fluid demonstrated non-Newtonian shear thinning behaviour and predominantly exhibited the characteristics of an entangled network. Inter-patient and inter-day variability in the viscosity of peritoneal fluid was observed. The solubility of the local anaesthetic lidocaine in peritoneal fluid was significantly higher (p < 0.05) when compared to phosphate-buffered saline. Interestingly, the dissolution rate of lidocaine was not significantly different between the synthetic and biological media. Importantly, and with relevance to intraperitoneal drug delivery systems, the sustained release of lidocaine from a thermosensitive gel formulation occurred at a significantly faster rate into peritoneal fluid. Collectively, these data demonstrate the variation between commonly used synthetic media and human peritoneal fluid. The differences in drug release rates observed illustrate the need for bio-relevant media, which ultimately would improve in vitro-in vivo correlation.

Evaluation of Dissolution in the Lower Intestine and Its Impact on the Absorption Process of High Dose Low Solubility Drugs

The purpose of this article was two-fold: first, to optimize a recently proposed two-stage single-compartment in vitro test for the evaluation of dissolution in the lower intestine with the mini-paddle apparatus in the fasted and fed state using two model high dose, low solubility drugs [sulfasalazine (Azulfidine) and micronized aprepitant] and one mesalamine colon targeting product (Asacol, 400 mg/tablet); second, to evaluate the impact of passive absorption from the lower intestine on the overall absorption process using three model high dose, low solubility drugs [micronized aprepitant, SB705498, and albendazole (Zentel)]. The intensity of agitation and the physicochemical characteristics of fluids simulating the environment in the distal ileum and the proximal colon were optimized and the importance of solid particles was evaluated. Dissolution data collected under conditions simulating the upper and lower intestine were coupled with physiologically based oral absorption modeling to simulate the average plasma levels or the average absorption process. Reliability of the modeling approach was evaluated based on previously collected data in adults. The impact of solid particles on dissolution in the lower intestine was found to be clinically insignificant for Asacol tablets, as well as for sulfasalazine (Azulfidine) and micronized aprepitant. Average plasma levels (micronized aprepitant and SB705498) and cumulative amount absorbed (albendazole) could be adequately simulated by referring only to events in the upper gastrointestinal lumen, indicating that the impact of absorption from the lower intestine on actual plasma levels was minimal. Dissolution of Asacol tablets and immediate release formulations in the lower intestine can be adequately evaluated by employing Level II biorelevant media. However, simulation of actual drug particle dissolution in the lower intestine is not typically necessary for adequate prediction of oral absorption from immediate release formulations containing discrete, dispersed particles of lipophilic drugs.

The impact of supersaturation level for oral absorption of BCS class IIb drugs, dipyridamole and ketoconazole, using in vivo predictive dissolution system: Gastrointestinal Simulator (GIS)

The development of formulations and the assessment of oral drug absorption for Biopharmaceutical Classification System (BCS) class IIb drugs is often a difficult issue due to the potential for supersaturation and precipitation in the gastrointestinal (GI) tract. The physiological environment in the GI tract largely influences in vivo drug dissolution rates of those drugs. Thus, those physiological factors should be incorporated into the in vitro system to better assess in vivo performance of BCS class IIb drugs. In order to predict oral bioperformance, an in vitro dissolution system with multiple compartments incorporating physiologically relevant factors would be expected to more accurately predict in vivo phenomena than a one-compartment dissolution system like USP Apparatus 2 because, for example, the pH change occurring in the human GI tract can be better replicated in a multi-compartmental platform. The Gastrointestinal Simulator (GIS) consists of three compartments, the gastric, duodenal and jejunal chambers, and is a practical in vitro dissolution apparatus to predict in vivo dissolution for oral dosage forms. This system can demonstrate supersaturation and precipitation and, therefore, has the potential to predict in vivo bioperformance of oral dosage forms where this phenomenon may occur. In this report, in vitro studies were performed with dipyridamole and ketoconazole to evaluate the precipitation rates and the relationship between the supersaturation levels and oral absorption of BCS class II weak base drugs. To evaluate the impact of observed supersaturation levels on oral absorption, a study utilizing the GIS in combination with mouse intestinal infusion was conducted. Supersaturation levels observed in the GIS enhanced dipyridamole and ketoconazole absorption in mouse, and a good correlation between their supersaturation levels and their concentration in plasma was observed. The GIS, therefore, appears to represent in vivo dissolution phenomena and demonstrate supersaturation and precipitation of dipyridamole and ketoconazole. We therefore conclude that the GIS has been shown to be a good biopredictive tool to predict in vivo bioperformance of BCS class IIb drugs that can be used to optimize oral formulations.

Mapping the intermediate digestion phases of human healthy intestinal contents from distal ileum and caecum at fasted and fed state conditions

OBJECTIVES

To investigate at the ultrastructural level, the colloidal phases formed in the lumen of the distal ileum and caecum of healthy adults.

METHODS

Cryogenic transmission electron microscopy (Cryo-TEM) was employed to image the intermediate colloidal phases of human intestinal contents collected from distal ileum and caecum of two healthy volunteers under fasted and fed state conditions.

KEY FINDINGS

In samples collected both in the fasted and fed states, Cryo-TEM study revealed the presence of large spherical unilamellar and occasionally bi-lamellar and oligolamellar vesicles with diameters ranging from 50 to 200 nm for both volunteers in distal ileum and caecum. Bilayer fragments were frequently observed in caecal samples. Plate-like structures resembling the morphology of cholesterol plates were visualised in all samples. Elongated structures were observed in the fed state in distal ileum and caecum for both volunteers, whereas no micellar structures could be detected for all samples.

CONCLUSIONS

This study provides a framework for understanding the structure of colloidal phases, and it may assist in elucidating the role of dosing conditions on drug absorption from the distal ileum and caecum.

In vitro and in silico characterisation of Tacrolimus released under biorelevant conditions

This work aims to better understand the in vivo behaviour of modified release (MR) formulations (Envarsus^® tablets and Advagraf^® capsules) using in vitro properties of tacrolimus and in silico simulations. The in silico concentration profiles of tacrolimus released from the MR formulations were predicted after building a three compartments PK model with GastroPlus™, and using the experimentally determined in vitro physico-chemical properties as input parameters. In vitro-in vivo correlations (IVIVC) were obtained after deconvolution of in vivo data from a clinical trial. The IVIVC showed that the in vitro dissolution was faster than the in vivo deconvoluted dissolution for Advagraf^®, while the in vitro dissolution was slightly slower than the in vivo deconvoluted dissolution for Envarsus^®. Population PK simulation showed that variability in the simulation was lower for Envarsus^® compared to Advagraf^®. The in silico predicted preferential absorption sites were the proximal and distal tract for Advagraf^® and Envarsus^®, respectively. The integration of experimental in vitro solubility, permeability and biorelevant dissolution data allowed to generate in silico tacrolimus concentrations for two different MR formulations. This permitted to compare the two formulations in a single PK profile, in a simulated population PK study and with respect to their absorption sites.

Oral uptake of nanoparticles: human relevance and the role of in vitro systems

Nanoparticles (NPs) present in environment, consumer and health products, food and medical applications lead to a high degree of human exposure and concerns about potential adverse effects on human health. For the general population, the exposure through contact with the skin, inhalation and oral uptake are most relevant. Since in vivo testing is only partly able to study the effects of human oral exposure, physiologically relevant in vitro systems are being developed. This review compared the three routes taking into account the estimated concentration, size of the exposed area, morphology of the involved barrier and translocation rate. The high amounts of NPs in food, the large absorption area and the relatively high translocation rate identified oral uptake as most important portal of entry for NPs into the body. Changes of NP properties in the physiological fluids, mechanisms to cross mucus and epithelial barrier, and important issues in the use of laboratory animals for oral exposure are mentioned. The ability of in vitro models to address the varying conditions along the oro-gastrointestinal tract is discussed, and requirements for physiologically relevant in vitro testing of orally ingested NPs are listed.

Can dosage form-dependent food effects be predicted using biorelevant dissolution tests? Case example extended release nifedipine

AIMS

Food intake is known to have various effects on gastrointestinal luminal conditions in terms of transit times, hydrodynamic forces and/or luminal fluid composition and can therefore affect the dissolution behavior of solid oral dosage forms. The aim of this study was to investigate and detect the dosage form-dependent food effect that has been observed for two extended-release formulations of nifedipine using in vitro dissolution tests.

METHODS

Two monolithic extended release formulations, the osmotic pump Adalat® XL 60mg and matrix-type Adalat® Eins 30mg formulation, were investigated with biorelevant dissolution methods using the USP apparatus III and IV under both simulated prandial states, and their corresponding quality control dissolution method. In vitro data were compared to published and unpublished in vivo data using deconvolution-based in vitro - in vivo correlation (IVIVC) approaches.

RESULTS

Quality control dissolution methods tended to overestimate the dissolution rate due to the excessive solubilizing capabilities of the sodium dodecyl sulfate (SDS)-containing dissolution media. Using Level II biorelevant media the dosage form dependent food effect for nifedipine was described well when studied with the USP apparatus III, whereas the USP apparatus IV failed to detect the positive food effect for the matrix-type dosage form.

CONCLUSIONS

It was demonstrated that biorelevant methods can serve as a useful tool during formulation development as they were able to qualitatively reflect the in vivo data.