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.

Oral biopharmaceutics tools: recent progress from partnership through the Pharmaceutical Education and Research with Regulatory Links collaboration.

OBJECTIVES: To summarise key contributions of the Pharmaceutical Education and Research with Regulatory Links (PEARRL) project (2016-2020) to the optimisation of existing and the development of new biopharmaceutics tools for evaluating the in vivo performance of oral drug products during the development of new drugs and at the regulatory level. KEY FINDINGS: Optimised biopharmaceutics tools: Based on new clinical data, the composition of biorelevant media for simulating the fed state conditions in the stomach was simplified. Strategies on how to incorporate biorelevant in vitro data of bio-enabling drug products into physiologically based pharmacokinetic (PBPK) modelling were proposed. Novel in vitro biopharmaceutics tools: Small-scale two-stage biphasic dissolution and dissolution-permeation setups were developed to facilitate understanding of the supersaturation effects and precipitation risks of orally administered drugs. A porcine fasted state simulated intestinal fluid was developed to improve predictions and interpretation of preclinical results using in vitro dissolution studies. Based on new clinical data, recommendations on the design of in vitro methodologies for evaluating the GI drug transfer process in the fed state were suggested. The optimized design of in vivo studies for investigating food effects: A food effect study protocol in the pig model was established which successfully predicted the food-dependent bioavailability of two model compounds. The effect of simulated infant fed state conditions in healthy adults on the oral absorption of model drugs was evaluated versus the fasted state and the fed state conditions, as defined by regulatory agencies for adults. Using PBPK modelling, the extrapolated fasted and infant fed conditions data appeared to be more useful to describe early drug exposure in infants, while extrapolation of data collected under fed state conditions, as defined by regulators for adults, failed to capture in vivo infant drug absorption. SUMMARY: Substantial progress has been made in developing an advanced suite of biopharmaceutics tools for streamlining drug formulation screening and supporting regulatory applications. These advances in biopharmaceutics were achieved through networking opportunities and research collaborations provided under the H2020 funded PEARRL project.

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.

Characteristics of Contents of Lower intestine in the 65-74 Years of Age Range Could Impact the Performance of Safe and Efficacious Modified Release Products.

We characterized the contents of distal ileum and proximal colon of older people from a pharmaceutical product performance perspective, under two extreme situations, i.e. 5 h after a glass of water to fasted volunteers (fasted state) and 5 h after a high-calorie, high-fat meal to fasted volunteers (fed state). Five males and three females (65-70 y) participated in a two-phase crossover study. Contents were collected via colonoscopy. In distal ileum, luminal pH was lower and buffer capacity was higher than in young adults; differences reached significance for pH in the fed state. In proximal colon, differences reached significance for pH/fasted state and for buffer capacity/both fasted and fed states. Aqueous fraction of contents contained more short chain fatty acids than previously observed in young adults. In distal ileum, osmolality was significantly higher than in young adults. In proximal colon, aqueous fraction in the fasted state was significantly lower and long chain fatty acids 5 h after meal was significantly higher than in young adults. Characteristics of contents of lower intestine that are relevant to the performance of certain modified release products differ between individuals 65-74 years old and young adults, the typical age group employed in safety and efficacy studies of oral drug products.

Ex vivo evaluation of degradation rates of metronidazole and olsalazine in distal ileum and in cecum: The impact of prandial state.

PURPOSE: Evaluate ex vivo the bacterial metabolism induced degradation rates of mesalamine (negative control), metronidazole and olsalazine in distal ileum and in cecum. METHODS: The contents of distal ileum and cecum were collected during colonoscopy under anaerobic conditions from twelve healthy adults in the fasted and in the fed state. To eliminate potential effects of enzymes that may exist in the fluid of lower intestine, each sample was ultracentrifuged and the precipitate was diluted with a volume of normal saline equivalent to that of the supernatant, after ultracentrifugation of intestinal contents from which the specific precipitate had been obtained. Degradation of the three model drugs in individual materials was evaluated anaerobically. RESULTS: Mesalamine was stable in all cases. Degradation rates of metronidazole and olsalazine were higher in cecum than in distal ileum, only in the fasted state; no trend could be observed in the fed state. Degradation rates of metronidazole and olsalazine were decreased in the fed state in the cecum; no trend could be observed in distal ileum. CONCLUSIONS: In the fasted state, bacterial activity is higher in cecum than in distal ileum. Food residues decrease bacterial metabolism degradation rates of drugs in cecum.

Mechanistic investigation of the negative food effect of modified release zolpidem.

AIMS: When administered orally as either an immediate or modified release dosage form, zolpidem demonstrates a negative food effect, i.e. decrease in Cmax and AUC. The aim of the study was to arrive at a better understanding of the absorption of this BCS class I compound in vivo and to simulate the observed plasma profiles using in vitro and in silico methods. METHODS: Pharmacokinetic profiles of zolpidem are presented from a bioavailability (8mg intravenous; 10mg immediate release Stilnox®; 10mg and 12.5mg modified release Ambien® CR) and from a food effect study (12.5mg modified release Ambien® CR). The dissolution behavior of the 12.5mg strength was investigated using compendial methods in the USP apparatus II and using biorelevant methods in the USP apparatus III and IV. The mean plasma profiles as well as selected individual plasma profiles were simulated with Simcyp® and GastroPlus™. The absorption behavior was additionally investigated using the Qgut model, which entails algebraic deconvolution of all individual profiles, incorporating both first pass gut and liver extraction. RESULTS: It was possible to simulate the mean plasma profiles using a "middle-out" approach, based on in vitro data combined with pharmacokinetic parameters obtained after intravenous administration, using PBPK software (Simcyp® and GastroPlus™), resulting in average fold error (AFE) values <1.5. Deconvolution verified that the in vivo absorption rate from the modified release formulation is controlled by the formulation in the fasted state, whereas in the fed state, the absorption rate is mainly controlled by gastric emptying. One-stage in vitro tests suggested that interactions with meal components, resulting in incomplete release, may be the source of the negative food effect for both the immediate and modified release formulations. CONCLUSIONS: The present study demonstrated that a combination of biorelevant dissolution testing with modeling approaches enables a mechanistic understanding of the absorption of zolpidem from various formulations and can serve as a useful biopharmaceutical approach for the development of modified release solid oral dosage forms.

Characteristics of the Human Upper Gastrointestinal Contents in the Fasted State Under Hypo- and A-chlorhydric Gastric Conditions Under Conditions of Typical Drug - Drug Interaction Studies.

OBJECTIVE: Evaluate the impact of reduced gastric acid secretion after administration of two acid-reducing agents on the physicochemical characteristics of contents of upper gastrointestinal lumen of fasted adults. MATERIALS AND METHODS: Eight healthy male adults, fasted from food for 12 h, participated in a three-phase crossover study. Phase 1: No drug treatment prior to aspirations. Phase 2: Oral administration of 40 mg pantoprazole at ~9 am the last 3 days prior to aspirations and at ~7 am on aspiration day. Phase 3: Oral administration of 20 mg famotidine at ~7 pm prior to aspirations and at ~7 am on aspiration day. Samples from the contents of upper gastrointestinal lumen were aspirated for 50 min, after administration of 240 ml table water at ~9 am. RESULTS: Reduction of gastric acid secretion was accompanied by reduced buffer capacity, chloride ion concentration, osmolality and surface tension in stomach and by increased pH (up to ~0.7 units) in upper small intestine during the first 50 min post-water administration. The mechanism of reduction of acid secretion seems to be important for the buffer capacity in stomach and for the surface tension in upper gastrointestinal lumen. CONCLUSIONS: Apart from gastric pH, reduced acid secretion affects physicochemical characteristics of contents of upper gastrointestinal lumen which may be important for the performance of certain drugs/products in the fasted state.

Characterization of Contents of Distal Ileum and Cecum to Which Drugs/Drug Products are Exposed During Bioavailability/Bioequivalence Studies in Healthy Adults.

PURPOSE: Characterize the contents of distal ileum and cecum in healthy adults under conditions simulating the bioavailability/bioequivelance studies of drug products in fasted and fed state. METHODS: Twelve males participated in a two-phase crossover study. Phase I: subjects remained fasted overnight plus 4.5 h in the morning prior to colonoscopy. Phase II: subjects remained fasted overnight, consumed breakfast in the morning, and abstain from food until colonoscopy, 4.5 h after breakfast. Upon sampling, volume, pH and buffer capacity were measured; after ultracentrifugation, supernatant was physicochemically characterized and non-liquid particles diameter was measured. RESULTS: In distal ileum, pH is ~8.1 and size of non-liquid particles is ~200 µm, regardless of dosing conditions; in fed state, liquid fraction was lower whereas osmolality and carbohydrate content were higher. In cecum, the environment was similar with previously characterized environment in the ascending colon; in fasted state, size of non-liquid particles is smaller than in distal ileum (~70 µm). Fluid composition in distal ileum is different from cecum, especially in fasted state. CONCLUSION: Differences in luminal environment between distal ileum and cecum may impact the performance of orally administered products which deliver drug during residence in lower intestine. Dosing conditions affect cecal environment more than in distal ileum.

Characterization of the ascending colon fluids in ulcerative colitis.

PURPOSE: To characterize the fluid composition in ascending colon of fasted adults with ulcerative colitis in relapse and in remission with a view to predicting variations on dosage form performance in the lower inflamed gut. METHODS: Twelve patients participated in a two-phase, crossover study. Enrollment to the relapse phase (Phase A) and designation of the remission state for the second colonoscopy (Phase B) were based on Clinical Rachmilewicz Index values. Samples were analyzed for pH and buffer capacity immediately upon collection. After ultracentrifugation, osmolality, surface tension, soluble protein, soluble carbohydrates, and the levels of ten bile acids, seven short-chain fatty acids (SCFAs), three long-chain fatty acids, triglycerides, diglycerides, monoglycerides, phosphatidylcholine, and cholesterol were measured. RESULTS: Total SCFAs are significantly decreased in relapse, but pH remains unaffected. Regardless of remission/relapse status, pH and isobutyric acid levels are lower than in healthy adults. Buffer capacity, osmolality, and soluble protein are higher than in healthy adults. Treatment with prednisolone increases the volume of intracolonic contents. CONCLUSION: Variations in fluid composition of the ascending colon with activity and severity of ulcerative colitis may have an impact on the performance of orally administered products that are targeted to release the therapeutic agent in the colon.

Characterization of the contents of ascending colon to which drugs are exposed after oral administration to healthy adults.

PURPOSE: To characterize the contents of the ascending colon in healthy adults under fasting and fed state conditions, with a view to designing in vitro studies to explain/predict dosage form performance in the lower gut. METHODS: Twelve healthy adults participated in a two-phase crossover study. In Phase A, subjects were fasted (water allowed) overnight plus 5 h in the morning prior to colonoscopy (fasted state). In Phase B, subjects were fasted overnight, consumed a standard breakfast (960 kcal) in the morning, and were offered a light lunch 4.5 h later. In this phase, colonoscopy was performed 1 h after lunch (fed state). Volume, pH, and buffer capacity of colonic contents were measured immediately upon collection. After ultracentrifugation, the supernatant was further characterized. RESULTS: Free water content, pH, surface tension, and isobutyrate levels were lower in fed than in fasted subjects. On the other hand, buffer capacity, osmolality, acetate, butyrate, cholate, and chenodeoxycholate levels were higher in fed subjects. Carbohydrate content; protein content; and levels of long chain fatty acids, phosphatidylcholine, and cholesterol were not affected significantly by prandial state. CONCLUSION: Composition of fluids in the ascending colon is affected by feeding. This may affect the performance of products designed to deliver drug to the colon.

Plasma profiles of lycopene after single oral and intravenous administrations in dogs.

The objectives of this study were to identify the factors limiting the absorption of purified lycopene after oral administration, and to comparatively assess plasma data sets after single oral and intravenous administrations in dogs to define the conditions for performing an absolute bioavailability study. Solubility of purified lycopene (all-trans, 93.5%) was determined in media simulating the conditions in the fasted and in the fed upper gastrointestinal lumen. After evaluating the plasma levels achieved following single administrations of purified lycopene powder to fasted and fed dogs at escalating doses (75-750 mg), a crossover study was performed in four fed female mongrel dogs at two phases. In phase I, one soft gelatine capsule (10 mg lycopene) with 500 mL milk was administered orally. In phase II, 500 mL milk was administered orally and 250 mL 5% dextrose containing 5 mg lycopene in the form of a binary system with hydroxypropyl-beta-cyclodextrin (HP-beta-CyD) was administered intravenously over 3.5 h. In-vitro and preliminary canine studies confirmed that, after oral administration of lycopene in solid form, arrival of lycopene into the systemic circulation was limited by lymphatic transport and, in addition, if the administered dose was higher than approximately 2 mg, by intralumenal solubility. During the first 50 h after single administrations to fed dogs, lycopene plasma levels were lower after intravenous than after oral administration. This could have been related to capacity limited elimination of lycopene and/or route-dependent disposition kinetics. Estimation of the amount of lycopene reaching the systemic circulation after oral and after intravenous administration requires separate estimations of total body clearance of lycopene.