Exploring gastrointestinal variables affecting drug and formulation behavior: Methodologies, challenges and opportunities

Tracking the journey: Gastrointestinal transit and intraluminal pH dynamics in aging populations using wireless motility capsule

INTRODUCTION

Gastrointestinal (GI) changes may alter drug absorption, potentially impacting both efficacy and safety of oral pharmacotherapy. However, the GI physiology is rarely studied in the aging population. This study aimed to explore GI transit time and pH in geriatric inpatients and older adults, and compare these findings with those from young volunteers.

METHODS

A prospective study was performed in geriatric inpatients and community-dwelling adults aged ≥ 75 years. GI transit and intraluminal pH were assessed by using a wireless motility capsule system. Participants' data were pooled with those from a previous study in healthy young volunteers (n = 11). Multivariable linear regression models were developed to identify explanatory variables for GI transit time and pH value.

RESULTS

We recruited 30 subjects (median age 80 [interquartile range (IQR) = 77-83] years). When compared to young volunteers (median age 21 [20-33]) years), geriatric inpatients (N = 8) exhibited prolonged gastric emptying times (median = 0.63 h [IQR = 0.32-0.86 h] vs median = 2.98 h [IQR = 1.50-20.35 h], p < 0.01). Community-dwelling older adults (N = 22) did not demonstrate delayed gastric emptying (median = 0.42 h [IQR = 0.36-0.53 h]; p = 0.85. Proton pump inhibitors (PPI) use was associated with increased gastric pH (median pH = 3.75 [IQR = 1.69-4.96] vs. non-PPI median pH = 1.28[IQR = 1.01-1.70]; p < 0.01) in the pooled analysis. The total older cohort had significantly lower small intestine pH compared to young group (median pH = 6.8 vs. 7.2; p < 0.01).

CONCLUSION

Older age did not necessarily alter GI physiology with respect to gastric emptying time and luminal pH values. Only geriatric inpatients exhibited delayed gastric emptying of the motility capsule as compared to young volunteers, while community-dwelling older adults did not. Prevalent PPI use in the aging population led to higher gastric pH levels, with substantial intersubject variability.

Enteric-Coated Capsules Providing Reliable Site-Specific Drug Delivery to the Distal Ileum

Nefecon, a targeted-release capsule formulation of budesonide approved for the reduction of proteinuria in adults with primary immunoglobulin A nephropathy, targets overproduction of galactose-deficient immunoglobulin A type 1 in the Peyer's patches at the gut mucosal level. To investigate whether the commercial formulation of Nefecon capsules reliably releases budesonide to the distal ileum, a human study was conducted with test capsules reproducing the delayed-release function of Nefecon capsules. Caffeine was included in the test capsules as a marker for capsule opening in the gut since it appears rapidly in saliva after release from orally administered dosage forms. Magnetic resonance imaging with black iron oxide was used to determine the capsule's position in the gut at the time caffeine was first measured in saliva and additionally to directly visualize dispersion of the capsule contents in the gut. In vitro dissolution results confirmed that the test capsules had the same delayed-release characteristics as Nefecon capsules. In 10 of 12 human volunteers, the capsule was demonstrated to open in the distal ileum; in the other two subjects, it opened just past the ileocecal junction. These results compared favorably with the high degree of variability seen in other published imaging studies of delayed-release formulations targeting the gut. The test capsules were shown to reliably deliver their contents to the distal ileum, the region with the highest concentration of Peyer's patches.

In Vitro Simulation of the Fasted Gastric Conditions and Their Variability to Elucidate Contrasting Properties of the Marketed Dabigatran Etexilate Pellet-Filled Capsules and Loose Pellets

Variability of the gastrointestinal tract is rarely reflected in in vitro test protocols but often turns out to be crucial for the oral dosage form performance. In this study, we present a generation method of dissolution profiles accounting for the variability of fasted gastric conditions. The workflow featured 20 biopredictive tests within the physiological variability. The experimental array was constructed with the use of the design of experiments, based on three parameters: gastric pH and timings of the intragastric stress event and gastric emptying. Then, the resulting dissolution profiles served as a training data set for the dissolution process modeling with the machine learning algorithms. This allowed us to generate individual dissolution profiles under a customizable gastric pH and motility patterns. For the first time ever, we used the method to successfully elucidate dissolution properties of two dosage forms: pellet-filled capsules and bare pellets of the marketed dabigatran etexilate product Pradaxa. We showed that the dissolution of capsules was triggered by mechanical stresses and thus was characterized by higher variability and a longer dissolution onset than observed for pellets. Hence, we proved the applicability of the method for the in vitro and in silico characterization of immediate-release dosage forms and, potentially, for the improvement of in vitro-in vivo extrapolation.

Syrupy herbal formulation of green bean pod extract of Phaseolus vulgaris L.: Formulation optimization by central composite design, and evaluation for anti-urolithiatic activity

The green bean pods of Phaseolus vulgaris L. are traditionally used as a folk remedy for treating calcium oxalate kidney stones. The current research aimed to develop a syrup formulation containing green bean pod extract for anti-urolithiatic activity. The syrup was prepared using a simple blending method and optimized through a central composite design (CCD) with two independent variables: the ratio of pod juice (PJ) to sugar solution (SS) ranging from 1:0.5 to 1:1.5, and the percentage of CMC from 0.2% to 0.4% w/v. These variables were analyzed for their impact on viscosity (CP) and sedimentation percentage, helping to identify the best formulation out of 13 variants. The finalized formulation (F-opt) underwent assessment for physicochemical characteristics such as organoleptic properties, viscosity, density, sedimentation rate, and stability. Additionally, a microbiological assessment was performed utilizing the spread plate method. Further, it was evaluated for in vitro, ex vivo, and in vivo anti-urolithiatic activity in rat models for 28 days and compared with that of the reference standard (Cystone syrup). Additionally, acute toxicity was assessed in albino Swiss mice. Histopathological evaluations were then conducted on the kidneys of the Wistar rats that had been used for the in vivo studies, providing insight into the treatment effects on kidney tissue structure. The optimized formulation (F-opt) was a green, viscous, clear syrup with a pH of 5.8, a viscosity of 256.38 CP, a density of 1.31 g/ml, and a sedimentation rate of 0.69%. The optimized formulation was found to be stable, showing no significant changes in physicochemical and microbiological properties. The results of the in vitro, ex vivo, and in vivo anti-urolithiatic studies indicated that the optimized formulation effectively inhibited the aggregation of calcium oxalate. The acute toxicity studies revealed no mortality or adverse effects for both the optimized formulation and pure bean pod juice at a dose of 2000 mg/kg body weight. Histopathological examination revealed that rats treated with the optimized formulation exhibited a significant reduction in both the number and size of calcium oxalate deposits within various parts of the renal tubules. It can be concluded that the syrupy formulation of Phaseolus vulgaris L. green bean pod extract demonstrated significant anti-urolithiatic activity. This activity could be due to its diuretic properties and its ability to inhibit the formation of calcium oxalate crystals. However, limitations of the study included a lack of elucidation of the mechanism and limited generalizability of the findings.

Advances in the Evaluation of Gastrointestinal Absorption Considering the Mucus Layer

Because of the increasing sophistication of formulation technology and the increasing polymerization of compounds directed toward undruggable drug targets, the influence of the mucus layer on gastrointestinal drug absorption has received renewed attention. Therefore, understanding the complex structure of the mucus layer containing highly glycosylated glycoprotein mucins, lipids bound to the mucins, and water held by glycans interacting with each other is critical. Recent advances in cell culture and engineering techniques have led to the development of evaluation systems that closely mimic the ecological environment and have been applied to the evaluation of gastrointestinal drug absorption while considering the mucus layer. This review provides a better understanding of the mucus layer components and the gastrointestinal tract's biological defense barrier, selects an assessment system for drug absorption in the mucus layer based on evaluation objectives, and discusses the overview and features of each assessment system.

Digitalizing the TIM-1 Model Using Computational Approaches─Part Two: Digital TIM-1 Model in GastroPlus

A TIM-1 model is an in vitro gastrointestinal (GI) simulator considering crucial physiological parameters that will affect the in vivo drug release process. The outcome of these experiments can indicate the critical bioavailability attributes (CBAs) that will impact the fraction absorbed in vivo. The model is widely used in the nonclinical stage of drug product development to assess the bioaccessible fraction of drugs for numerous candidate formulations. In this work, we developed a digital TIM-1 model in the GastroPlus platform. In a first step, we performed validation experiments to assess the luminal concentrations and bioaccessible fractions for two marker compounds. The digital TIM-1 was able to adequately reflect the luminal concentrations and bioaccessible fractions of these markers under different prandial conditions, confirming the appropriate integration of mass transfer in the TIM-1 model. In a second set of experiments, a case example with PF-07059013 was performed, where luminal concentrations and bioaccessible fractions were predicted for 200 and 1000 mg doses under fasted and achlorhydric conditions. Experimental and simulated data pointed out that the achlorhydric effect was more pronounced at the 1000 mg dose, showing a solubility-limited dissolution and, consequently, decreased bioaccessible fraction. Toward future applications, the digital TIM-1 model will be thoroughly applied to explore a link between in vitro and in vivo outcomes based on more case examples with model compounds with the access of TIM-1 and plasma data. Ideally, this digital TIM-1 can be directly used in GastroPlus to explore an in vitro-in vivo correlation (IVIVC) between the fraction dissolved (digital TIM-1 settings) and the fraction absorbed (human PBPK settings).

Stochastic Differential Equation-based Mixed Effects Model of the Fluid Volume in the Fasted Stomach in Healthy Adult Human

The rate and extent of drug dissolution and absorption from a solid oral dosage form depend largely on the fluid volume along the gastrointestinal tract. Hence, a model built upon the gastric fluid volume profiles can help to predict drug dissolution and subsequent absorption. To capture the great inter- and intra-individual variability (IAV) of the gastric fluid volume in fasted human, a stochastic differential equation (SDE)-based mixed effects model was developed and compared with the ordinary differential equation (ODE)-based model. Twelve fasted healthy adult subjects were enrolled and had their gastric fluid volume measured before and after consumption of 240 mL of water at pre-determined intervals for up to 2 hours post ingestion. The SDE- and ODE-based mixed effects models were implemented and compared using extended Kalman filter algorithm via NONMEM. The SDE approach greatly improved the goodness of fit compared with the ODE counterpart. The proportional and additive measurement error of the final SDE model decreased from 14.4 to 4.10% and from 17.6 to 4.74 mL, respectively. The SDE-based mixed effects model successfully characterized the gastric volume profiles in the fasted healthy subjects, and provided a robust approximation of the physiological parameters in the very dynamic system. The remarkable IAV could be further separated into system dynamics terms and measurement error terms in the SDE model instead of only empirically attributing IAV to measurement errors in the traditional ODE method. The system dynamics were best captured by the random fluctuations of gastric emptying coefficient Kge.

Characterization of neonatal and infant enterostomy fluids - Part II: Drug solubility

Previous research revealed marked differences in the composition of intestinal fluids between infants and adults. To explore the impact on the solubilization of orally administered drugs, the present study assessed the solubility of five poorly water-soluble, lipophilic drugs in intestinal fluid pools from 19 infant enterostomy patients (infant HIF). For some but not all drugs, the average solubilizing capacity of infant HIF was similar to that of HIF obtained from adults (adult HIF) in fed conditions. Commonly used fed state simulated intestinal fluids (FeSSIF(-V2)) predicted fairly well drug solubility in the aqueous fraction of infant HIF, but did not account for the substantial solubilization by the lipid phase of infant HIF. Despite similarities in the average solubilities of some drugs in infant HIF and adult HIF or SIF, the underlying solubilization mechanisms likely differ, considering important compositional differences (e.g., low bile salt levels). Finally, the huge variability in composition of infant HIF pools resulted in a highly variable solubilizing capacity, potentially causing variations in drug bioavailability. The current study warrants future research focusing on (i) understanding the mechanisms underlying drug solubilization in infant HIF and (ii) evaluating the sensitivity of oral drug products to interpatient variations in drug solubilization.

Disentangling the links between gastric emptying and binge eating v. purging in eating disorders using a case-control design

BACKGROUND

Prior work supports delayed gastric emptying in anorexia nervosa and bulimia nervosa (BN) but not binge-eating disorder, suggesting that neither low body weight nor binge eating fully accounts for slowed gastric motility. Specifying a link between delayed gastric emptying and self-induced vomiting could offer new insights into the pathophysiology of purging disorder (PD).

METHODS

Women (N = 95) recruited from the community meeting criteria for DSM-5 BN who purged (n = 26), BN with nonpurging compensatory behaviors (n = 18), PD (n = 25), or healthy control women (n = 26) completed assessments of gastric emptying, gut peptides, and subjective responses over the course of a standardized test meal under two conditions administered in a double-blind, crossover sequence: placebo and 10 mg of metoclopramide.

RESULTS

Delayed gastric emptying was associated with purging with no main or moderating effects of binge eating in the placebo condition. Medication eliminated group differences in gastric emptying but did not alter group differences in reported gastrointestinal distress. Exploratory analyses revealed that medication caused increased postprandial PYY release, which predicted elevated gastrointestinal distress.

CONCLUSIONS

Delayed gastric emptying demonstrates a specific association with purging behaviors. However, correcting disruptions in gastric emptying may exacerbate disruptions in gut peptide responses specifically linked to the presence of purging after normal amounts of food.

Comparing the gastric emptying of 240 mL and 20 mL water by MRI and caffeine salivary tracer technique

Gastrointestinal fluid volumes are a crucial parameter for dissolution and absorption of orally taken medications. Most often 240 mL are used in clinical standard setups. Nonetheless, surveys in patient populations revealed dramatically lower volumes for intake of oral medications in real life and even in some clinical studies reduced fluid volumes are common. These reductions might have serious impact on pharmacokinetics. Thus, it was the aim of this study to compare the gastric emptying of 240 mL and 20 mL of water in 8 healthy volunteers. For investigation of gastric fluid volumes Magnetic Resonance Imaging with strongly T2 weighted sequences was used. Gastric emptying was additionally quantified via caffeine pharmacokinetics measured in saliva. The absolute gastric volumes after intake of 240 mL or 20 mL obviously differed by factor 10 but relative gastric emptying expressed as fraction per time was nearly comparable. Only slighter slower emptying after intake of 20 mL was observed. Salivary caffeine pharmacokinetics representing mass transfer from stomach to small intestine after intake of different volumes did not differ. The absorbed caffeine fraction and emptied gastric volume fraction correlated well after intake of 240 mL, but not after intake of 20 mL, indicating a higher influence of secretion on gastric volume measurements after intake of smaller volumes. Relative gastric emptying as measured with MRI and salivary caffeine method was only slightly delayed, thus transfer of orally administered drug fraction could be comparable even with lower fluid intake as can be seen by comparable caffeine pharmacokinetics. Nonetheless, the considerably reduced volumes might interfere with dissolution and absorption.

Comparing Salivary Caffeine Kinetics of 13C and 12C Caffeine for Gastric Emptying of 50 mL Water

Gastric water emptying as a critical parameter for oral drug absorption can be investigated by several imaging techniques or by the interpretation of pharmacokinetics of appropriate substances. Recently introduced salivary caffeine kinetics is a valuable tool, but the required caffeine abstinence limits its applicability. To avoid the caffeine abstinence, stable isotope-labeled caffeine might be used, but the representability and transferability of kinetics for evaluation of gastric emptying must be demonstrated. Thus, salivary caffeine pharmacokinetics were compared for naturally occurring ¹²C-caffeine and ¹³C₃-caffeine after the administration of water under fasting conditions in six healthy young subjects. For this purpose, an ice capsule containing the two caffeine species was administered with 50 mL tap water. Gastric water emptying was simultaneously quantified using magnetic resonance imaging (MRI). Gastric emptying of 50 mL of water could be successfully evaluated. The salivary caffeine kinetics of ¹³C₃- and ¹²C-caffeine were nearly congruent and showed good linear correlations in all subjects, with a mean correlation coefficient of 0.96 in pooled data. Thus, the substitution of natural ¹²C caffeine with stable isotope-labeled ¹³C₃-caffeine offers the opportunity for broader application of the salivary caffeine gastric emptying technique and increases the robustness of the method against environmental contamination with caffeine.

Concomitant administration of proton pump inhibitors does not significantly affect clinical outcomes in metastatic breast cancer patients treated with ribociclib

BACKGROUND

Gastric pH changes by proton-pump-inhibitors (PPIs) were found to affect progression-free survival (PFS) in metastatic breast cancer (mBC) patients treated with palbociclib. The current study was aimed at investigating whether the same effect could occur in patients treated with ribociclib.

PATIENTS AND METHODS

Patients with hormone-positive/HER-2-negative mBC candidates for first-line treatment with ribociclib were enrolled in this retrospective-cohort study. Patients were classified as "no concomitant PPIs" or "concomitant PPIs"; PPI administration covered the entire or not less than 2/3 of treatment with ribociclib. All clinical interventions were made according to clinical practice.

RESULTS

A total of 128 patients were consecutively enrolled in the study; 78 belonged to the "no concomitant PPIs" group and 50 to the "concomitant PPIs" group. One hundred and six patients were endocrine-sensitive and received ribociclib and letrozole, while 22 were endocrine-resistant and were treated with ribociclib and fulvestrant. The most prescribed PPI was lansoprazole. According to PFS, patients taking PPIs had a PFS almost superimposable to those assuming ribociclib and endocrine therapy alone (35.3 vs. 49.2 months, p = 0.594). No difference in PFS was observed in estrogen-sensitive or estrogen-resistant mBC in the presence or absence of concomitant PPI treatment (p = 0.852). No correlation with adverse events was found including grade>2 hematological toxicities.

CONCLUSIONS

The present study supports the hypothesis that the concomitant use of PPIs does not compromise the efficacy of ribociclib in a real-life setting.

Osteoporosis treatment with risedronate: a population pharmacokinetic model for the description of its absorption and low plasma levels

To develop a population pharmacokinetic model that describes the absorption and low plasma levels of risedronate in the body. The impact of patients' characteristics on risedronate kinetics is investigated. Simulations revealed the high variability in the concentration levels after different dosage schemes. No dosage adjustment is required in renal impairment.

INTRODUCTION

Risedronate exhibits very low plasma levels and high residence time in the body. The aim of this study is to describe and explain the risedronate transit through the body. The impact of volunteers' characteristics on the kinetics of risedronate is also investigated. Simulations are used to compare the risedronate plasma levels after different dosage schemes and assess the need for dose adjustment in patients with impaired kidney functionality.

METHODS

Plasma concentration-time data were obtained from a four-period, two sequence, single-dose, crossover bioequivalence study. The effects of several covariates (e.g., weight, albumin, creatinine, alkaline phosphatase, and calcium) on model parameters were tested. Non-linear mixed-effect modeling was applied and a variety of models were evaluated placing emphasis on absorption and disposition properties. The modeling and simulation work was implemented in Monolix^TM 2020R1.

RESULTS

Following oral administration, the kinetics of risedronate was best described by a two-compartment model with lag time, first-order absorption, and elimination. The extent of peripheral distribution (i.e., bones) was found to be remarkably high. No volunteer characteristics were identified to affect significantly the disposition of risedronate. Using simulations, risedronate plasma profiles were obtained for different doses and frequencies of administration.

CONCLUSION

The absorption and disposition kinetics of risedronate were successfully characterized. Simulations revealed the high discrepancy in the concentration levels observed after different dosage regimens, implying the safety profile of risedronate. In virtual patients with renal impairment, the blood levels of risedronate are increased, but not in an extent requiring dose adaptation.

An Assessment of Occasional Bio-Inequivalence for BCS1 and BCS3 Drugs: What are the Underlying Reasons?

Despite having adequate solubility properties, bioequivalence (BE) studies performed on immediate release formulations containing BCS1/3 drugs occasionally fail. By systematically evaluating a set of 17 soluble drugs where unexpected BE failures have been reported and comparing to a set of 29 drugs where no such reports have been documented, a broad assessment of the risk factors leading to BE failure was performed. BE failures for BCS1/3 drugs were predominantly related to changes in C_max rather than AUC. C_max changes were typically modest, with minimal clinical significance for most drugs. Overall, drugs with a sharp plasma peak were identified as a key factor in BE failure risk. A new pharmacokinetic term (t½C_max) is proposed to identify drugs at higher risk due to their peak plasma profile shape. In addition, the analysis revealed that weak acids, and drugs with particularly high gastric solubility are potentially more vulnerable to BE failure, particularly when these features are combined with a sharp C_max peak. BCS3 drugs, which are often characterised as being more vulnerable to BE failure due to their potential for permeation and transit to be altered, particularly by excipient change, were not in general at greater risk of BE failures. These findings will help to inform how biowaivers may be optimally applied in the future.

Effect of obesity on gastrointestinal transit, pressure and pH using a wireless motility capsule

BACKGROUND

Despite the increasing prevalence and medical burden of obesity, the understanding of gastrointestinal physiology in obesity is scarce, which hampers drug development.

AIM

To investigate the effect of obesity and food intake on gastrointestinal transit, pressure and pH.

MATERIAL AND METHODS

An exploratory cross-sectional study using a wireless motility capsule (SmartPill©) was performed in 11 participants with obesity and 11 age- and gender-matched participants with normal weight (group) in fasted and fed state (visit). During the first visit, the capsule was ingested after an overnight fast. During a second visit, the capsule was ingested after a nutritional drink to simulate fed state. Linear mixed models were constructed to compare segmental gastrointestinal transit, pressure and pH between groups (obesity or control) and within every group (fasted or fed).

RESULTS

Food intake slowed gastric emptying in both groups (both P < 0.0001), though food-induced gastric contractility was higher in participants with obesity compared to controls (P = 0.02). In the small intestine, a higher contractility (P = 0.001), shorter transit (P = 0.04) and lower median pH (P = 0.002) was observed in participants with obesity compared to controls. No differences were observed for colonic measurements.

CONCLUSION

Obesity has a profound impact on gastrointestinal physiology, which should be taken into account for drug development.

Oral lipid nanomedicines: Current status and future perspectives in cancer treatment

Oral anticancer drugs have earned a seat at the table, as the need for homecare treatment in oncology has increased. Interest in this field is growing as a result of their proven efficacy, lower costs and positive patient uptake. However, the gastrointestinal barrier is still the main obstacle to surmount in chemotherapeutic oral delivery. Anticancer nanomedicines have been proposed to solve this quandary. Among these, lipid nanoparticles are described to be efficiently absorbed while protecting drugs from early degradation in hostile environments. Their intestinal lymphatic tropism or mucoadhesive/penetrative properties give them unique characteristics for oral administration. Considering that chronic cancer cases are increasing over time, it is important to be able to provide treatments with low toxicity and low prices. The challenges, opportunities and therapeutic perspectives of lipid nanoparticles in this area will be discussed in this review, taking into consideration the pre-clinical and clinical progress made in the last decade.

Enabling modular dosage form concepts for individualized multidrug therapy: Expanding the design window for poorly water-soluble drugs

Multidrug dosage forms (aka combination dosage forms, polypills, etc.) create value for patients through reduced pill burdens and simplified administration to improve adherence to therapy. Enhanced flexibility of multidrug dosage forms would provide further opportunities to better match emerging needs for individualized therapy. Through modular dosage form concepts, one approach to satisfy these needs is to adapt multidrug dosage forms to a wider variety of drugs, each with a variety of doses and release profiles. This study investigates and technically explores design requirements for extending the capability of modular multidrug dosage form concepts towards individualization. This builds on our recent demonstration of independent tailoring of dose and drug release, which is here extended towards poorly water-soluble drugs. The challenging design requirement of carrying higher drug loads in smaller volumes to accommodate multiple drugs at their clinical dose is here met regarding dose and release performance. With a modular concept, we demonstrate high precision (<5% RSD) in dose and release performance of individual modules containing felodipine or naproxen in Kollidon VA64 at both a wide drug loading range (5% w/w and 50% w/w drug) and a small module size (3.6 mg). In a forward-looking design-based discussion, further requirements are addressed, emphasizing that reproducible individual module performance is predictive of dosage form performance, provided the modules are designed to act independently. Therefore, efforts to incorporate progressively higher drug loads within progressively smaller module volumes will be crucial to extend the design window further towards full flexibility of future dosage forms for individualized multidrug therapy.

In vivo dissolution of poorly water-soluble drugs: Proof of concept based on fluorescence bioimaging

In vitro‒in vivo correlation (IVIVC) of solid dosage forms should be established basically between in vitro and in vivo dissolution of active pharmaceutical ingredients. Nevertheless, in vivo dissolution profiles have never been accurately portrayed. The current practice of IVIVC has to resort to in vivo absorption fractions (F_a). In this proof-of-concept study, in vivo dissolution of a model poorly water-soluble drug fenofibrate (FNB) was investigated by fluorescence bioimaging. FNB crystals were first labeled by near-infrared fluorophores with aggregation-caused quenching properties. The dyes illuminated FNB crystals but quenched immediately and absolutely once been released into aqueous media, enabling accurate monitoring of residual drug crystals. The linearity established between fluorescence and crystal concentration justified reliable quantification of FNB crystals. In vitro dissolution was first measured following pharmacopoeia monograph protocols with well-documented IVIVC. The synchronicity between fluorescence and in vitro dissolution of FNB supported using fluorescence as a measure for determination of dissolution. In vitro dissolution correlated well with in vivo dissolution, acquired by either live or ex vivo imaging. The newly established IVIVC was further validated by correlating both in vitro and in vivo dissolution with F_a obtained from pharmacokinetic data.

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.

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

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

Pharmacomagnetography to evaluate the performance of magnetic enteric-coated tablets in the human gastrointestinal tract

A magnetic enteric-coated tablet containing diclofenac sodium was produced, and its performance under physiological and disturbed gastrointestinal motility was assessed through pharmacomagnetography analysis. In vitro studies were performed using conventional methods and in vivo studies were conducted on healthy volunteers before (control) and after domperidone administration. The magnetic tablet's gastrointestinal (GI) transit and disintegration process were monitored using the Alternating Current Biosusceptometry sensors combined with drug plasmatic concentration. The Gastric Residence Time, Colon Arrival Time, Small Bowel Transit Time, Disintegration Time and the pharmacokinetics parameters were calculated. The pH-dependent polymers used to coat the magnetic tablets were able to avoid the premature drug release on gastric or small intestine simulated medium. Gastric Residence Time was accelerated compared with the control group (p < 0.01). No significant differences were found regarding small bowel transit, colon arrival, disintegration process, or pharmacokinetics parameters. A strong correlation between magnetic monitoring and pharmacokinetics parameters analysis was determinant to evaluate the efficiency in the drug delivery at a specific site in the human gastrointestinal tract. In addition, a tablet with a damaged coating was used as a proof of concept to show the suitability of our methodology to evaluate the tablet. Our study showed that pharmacomagnetography is a multi-instrumental approach towards assessing drug delivery and bioavailability.

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.

Characterization of gastrointestinal transit and luminal conditions in pigs using a telemetric motility capsule

Within preclinical research, the pig has become an important model in regulatory toxicology and pharmacokinetics, to assess oral dosage forms and to compare different formulation strategies. In addition, there are emerging application of the pig model to asses clinical dosing conditions in the fasted and fed state. In this study, the gastrointestinal transit conditions in male landrace pigs were studied with a telemetric motility capsule under fasted and postprandial conditions. The whole gut transit time (WGTT) was determined by administering a SmartPill® capsule to four landrace pigs, under both fasted and fed state conditions in a cross-over study design. Overall, this study found that small intestinal transit in landrace pigs ranged from 2.3 - 4.0 h, and was broadly similar to reported human estimates and was not affected by the intake conditions. Gastric emptying was highly variable and prolonged in landrace pigs ranging from 20 - 233 h and up to 264 h in one specific case. Under dynamic conditions pigs have a low gastric pH comparable to humans, however a high variability under fasted conditions could be observed. The comparison of the data from this study with a recent similar study in beagle dogs revealed major differences between gastric maximum pressures observed in landrace pigs and dogs. In the porcine stomach maximum pressures of up to 402 mbar were observed, which are comparable to reported human data. Intestinal maximum pressures in landrace pigs were in the same range as in humans. Overall, the study provides new insights of gastrointestinal conditions in landrace pigs, which can lead to more accurate interpretation of in vivo results obtained of pharmacokinetic studies in preclinical models. While small intestinal transit conditions, GI pH and pressures were similar to humans, the prolonged gastric emptying observed in pigs need to be considered in assessing the suitability of the pig model for assessing in vivo performance of large non-disintegrated oral drug products.

In Vitro Biopredictive Methods: A Workshop Summary Report

This workshop report summarizes the proceedings of Day 1 of a three-day workshop on "Current State and Future Expectations of Translational Modeling Strategies to Support Drug Product Development, Manufacturing Changes and Controls". Physiologically based biopharmaceutics models (PBBM) are tools which enable the drug product quality attributes to be linked to the in vivo performance. These tools rely on key quality inputs in order to provide reliable predictions. After introducing the objectives of the workshop and the expectations from the breakout sessions, Day 1 of the workshop focused on the best practices and challenges in measuring in vitro inputs needed for modeling, such as the drug solubility, the dissolution rate of the drug product, potential precipitation of the drug and drug permeability. This paper reports the podium presentations and summarizes breakout session discussions related to A) the best strategies for determining solubility, supersaturation and critical supersaturation; B) the best strategies for the development of biopredictive (clinically relevant) dissolution methods; C) the challenges associated with describing gastro-intestinal systems parameters such as mucus, liquid volume and motility; and D) the challenges with translating biopharmaceutical measures of drug permeability along the gastrointestinal tract to a meaningful model parameter.

Independent Tailoring of Dose and Drug Release via a Modularized Product Design Concept for Mass Customization

Independent individualization of multiple product attributes, such as dose and drug release, is a crucial overarching requirement of pharmaceutical products for individualized therapy as is the unified integration of individualized product design with the processes and production that drive patient access to such therapy. Individualization intrinsically demands a marked increase in the number of product variants to suit smaller, more stratified patient populations. One established design strategy to provide enhanced product variety is product modularization. Despite existing customized and/or modular product design concepts, multifunctional individualization in an integrated manner is still strikingly absent in pharma. Consequently, this study aims to demonstrate multifunctional individualization through a modular product design capable of providing an increased variety of release profiles independent of dose and dosage form size. To further exhibit that increased product variety is attainable even with a low degree of product modularity, the modular design was based upon a fixed target dosage form size of approximately 200 mm3 comprising two modules, approximately 100 mm3 each. Each module contained a melt-extruded and molded formulation of 40% w/w metoprolol succinate in a PEG1500 and Kollidon® VA64 erodible hydrophilic matrix surrounded by polylactic acid and/or polyvinyl acetate as additional release rate-controlling polymers. Drug release testing confirmed the generation of predictable, combined drug release kinetics for dosage forms, independent of dose, based on a product's constituent modules and enhanced product variety through a minimum of six dosage form release profiles from only three module variants. Based on these initial results, the potential of the reconfigurable modular product design concept is discussed for unified integration into a pharmaceutical mass customization/mass personalization context.

Progress in the design and development of "fast-dissolving" electrospun nanofibers based drug delivery systems - A systematic review

Electrospinning has emerged as most viable approach for the fabrication of nanofibers with several beneficial features that are essential to various applications ranging from environment to biomedicine. The electrospun nanofiber based drug delivery systems have shown tremendous advancements over the controlled and sustained release complemented from their high surface area, tunable porosity, mechanical endurance, offer compatible environment for drug encapsulation, biocompatibility, high drug loading and tailorable release characteristics. The dosage formulation of poorly water-soluble drugs often faces several challenges including complete dissolution with maximum therapeutic efficiency over a short period of time especially through oral administration. In this context, challenges associated with the dosage formulation of poorly-water soluble drugs can be addressed through combining the beneficial features of electrospun nanofibers. This review describes major developments progressed in the preparation of electrospun nanofibers based "fast dissolving" drug delivery systems by employing variety of polymers, drug molecules and encapsulation approaches with primary focus on oral delivery. Furthermore, the review also highlights current scientific challenges and provide an outlook with regard to future prospectus.

In Vitro-In Vivo Correlation for Solid Dispersion of a Poorly Water-Soluble Drug Efonidipine Hydrochloride

The aim of this present study was to investigate the ability of different dissolution methods to predict the in vivo performance of efonidipine hydrochloride (EFH). The solid dispersions of EFH were prepared by solvent evaporation method with HPMC-AS as matrix and urea as a pH adjusting agent. The paddle method, the open-loop, and the closed-loop flow-through cell methods were studied. In the study, Weibull's model was the best fit to explain release profiles. The pharmacokinetics behaviors of two kinds of solid dispersions with different release rate were investigated in comparison to the EFH after oral administration in rats. In vivo absorption was calculated by a numerical deconvolution method. In the study, the level A in vivo and in vitro correlation (IVIVC) was utilized. The correlation coefficient was calculated and interpreted by means of linear regression analysis (Origin.Pro.8.5 software). As a result, excellent IVIVC for solid dispersions and crude drug (r² = 0.9352-0.9916) was obtained for the dissolution rate determined with flow-through cell open-loop system in phosphate buffer solution with 0.1% (w/v) polysorbate 80 at pH 6.5, the flow-rate of 4 mL/min. In addition, the self-assembled flow cell system had good repeatability and accuracy. The dissolution rate of the solid dispersion could be slowed down by the flow-through method, and the difference caused by preparation was significantly distinguished. The study demonstrated that flow-through cell method of the open-loop, compared with paddle method, was suitable for predicting in vivo performance of EFH solid dispersions.

A Mechanistic Physiologically-Based Biopharmaceutics Modeling (PBBM) Approach to Assess the In Vivo Performance of an Orally Administered Drug Product: From IVIVC to IVIVP

The application of in silico modeling to predict the in vivo outcome of an oral drug product is gaining a lot of interest. Fully relying on these models as a surrogate tool requires continuous optimization and validation. To do so, intraluminal and systemic data are desirable to judge the predicted outcomes. The aim of this study was to predict the systemic concentrations of ibuprofen after oral administration of an 800 mg immediate-release (IR) tablet to healthy subjects in fasted-state conditions. A mechanistic oral absorption model coupled with a two-compartmental pharmacokinetic (PK) model was built in Phoenix WinNonlinWinNonlin^® software and in the GastroPlus™ simulator. It should be noted that all simulations were performed in an ideal framework as we were in possession of a plethora of in vivo data (e.g., motility, pH, luminal and systemic concentrations) in order to evaluate and optimize these models. All this work refers to the fact that important, yet crucial, gastrointestinal (GI) variables should be integrated into biopredictive dissolution testing (low buffer capacity media, considering phosphate versus bicarbonate buffer, hydrodynamics) to account for a valuable input for physiologically-based pharmacokinetic (PBPK) platform programs. While simulations can be performed and mechanistic insights can be gained from such simulations from current software, we need to move from correlations to predictions (IVIVC → IVIVP) and, moreover, we need to further determine the dynamics of the GI variables controlling the dosage form transit, disintegration, dissolution, absorption and metabolism along the human GI tract. Establishing the link between biopredictive in vitro dissolution testing and mechanistic oral absorption modeling (i.e., physiologically-based biopharmaceutics modeling (PBBM)) creates an opportunity to potentially request biowaivers in the near future for orally administered drug products, regardless of its classification according to the Biopharmaceutics Classification System (BCS).

Labrasol® is an efficacious intestinal permeation enhancer across rat intestine: Ex vivo and in vivo rat studies

Labrasol® ALF (Labrasol®), is a non-ionic surfactant excipient primarily used as a solubilising agent. It was investigated here as an intestinal permeation enhancer in isolated rat colonic mucosae in Ussing chamber and in rat in situ intestinal instillations. Labrasol® comprises mono-, di- and triglycerides and mono- and di- fatty acid esters of polyethylene glycol (PEG)-8 and free PEG-8, with caprylic (C₈)- and capric acid (C₁₀) as the main fatty acids. Source components of Labrasol® as well as Labrasol® modified with either C₈ or C₁₀ as the sole fatty acid components were also tested to determine which element of Labrasol® was responsible for its permeability-enhancing properties. Labrasol® (4, 8 mg/mL) enhanced the transport of the paracellular markers, [¹⁴C] mannitol, FITC-dextran 4000, and FITC-insulin across colonic mucosae. The enhancement was non-damaging, transient, and molecular weight-dependent. The PEG ester fraction of Labrasol® also had enhancing properties. When insulin was administered with Labrasol® in instillations, it had a relative bioavailability of 7% in jejunum and 12% in colon. C₈- and C₁₀ versions of Labrasol® and the PEG ester fraction also induced similar bioavailability values in jejunal instillations: 6, 5 and 7% respectively. Inhibition of lipases in instillations did not reduce the efficacy of Labrasol®, suggesting that its mechanism as a PE is not simply due to liberated medium chain fatty acids. Labrasol® acts as an efficacious intestinal permeation enhancer and has potential for use in oral formulations of macromolecules and BCS Class III molecules.

Successful oral delivery of poorly water-soluble drugs both depends on the intraluminal behavior of drugs and of appropriate advanced drug delivery systems

Poorly water-soluble drugs continue to be a problematic, yet important class of pharmaceutical compounds for treatment of a wide range of diseases. Their prevalence in discovery is still high, and their development is usually limited by our lack of a complete understanding of how the complex chemical, physiological and biochemical processes that occur between administration and absorption individually and together impact on bioavailability. This review defines the challenge presented by these drugs, outlines contemporary strategies to solve this challenge, and consequent in silico and in vitro evaluation of the delivery technologies for poorly water-soluble drugs. The next steps and unmet needs are proposed to present a roadmap for future studies for the field to consider enabling progress in delivery of poorly water-soluble compounds.

Topography of Simulated Intestinal Equilibrium Solubility

Oral administration of a solid dosage form requires drug dissolution in the gastrointestinal tract before absorption. Solubility is a key factor controlling dissolution, and it is recognized that, within the intestinal tract, this is influenced by the luminal fluid pH, amphiphile content, and composition. Various simulated intestinal fluid recipes have been introduced to mimic this behavior and studied using a range of different experimental techniques. In this article, we have measured equilibrium solubility utilizing a novel four component mixture design (4CMD) with biorelevant amphiphiles (bile salt, phospholipid, oleate, and monoglyceride) within a matrix of three pH values (5, 6, and 7) and total amphiphile concentrations (11.7, 30.6, and 77.5 mM) to provide a topographical and statistical overview. Three poorly soluble drugs representing acidic (indomethacin), basic (carvedilol), and neutral (fenofibrate) categories have been studied. The macroscopic solubility behavior agrees with literature and exhibits an overall increasing solubility from low pH and total amphiphile concentration to high pH and total amphiphile concentration. Within the matrix, all three drugs display different topographies, which can be related to the statistical effect levels of the individual amphiphiles or amphiphile interactions on solubility. The study also identifies previously unreported three and four way factor interactions notably between bile salt, phospholipid, pH, and total amphiphile concentration. In addition, the results also reveal that solubility variability is linked to the number of amphiphiles and the respective ratios in the measurement fluid, with the minimum variation present in systems containing all four amphiphiles. The individual 4CMD experiments within the matrix can be linked to provide a possible intestinal solubility window for each drug that could be applied in PBPK modeling systems. Overall the approach provides a novel overview of intestinal solubility topography along with greater detail on the impact of the various factors studied; however, each matrix requires 351 individual solubility measurements. Further studies will be required to refine the experimental protocol in order the maximize information garnered while minimizing the number of measurements required.

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.

A review on 5-aminosalicylic acid colon-targeted oral drug delivery systems

Site-specific colon drug delivery is a practical approach for the treatment of local diseases of the colon with several advantages such as rapid onset of action and reduction of the dosage of the drug as well as minimization of harmful side effects. 5-aminosalicylic acid (5-ASA) is a drug of choice in the treatment of inflammatory bowel disease and colitis. For the efficient delivery of this drug, it is vital to prevent 5-ASA release in the upper part of the gastrointestinal tract and to promote its release in the proximal colon. Different approaches including chemical manipulation of drug molecule for production of prodrugs or modification of drug delivery systems using pH-dependent, time-dependent and/or bacterially biodegradable materials have been tried to optimize 5-ASA delivery to the colon. In the current review, the different strategies utilized in the design and development of an oral colonic delivery dosage form of 5-ASA are presented and discussed.

A novel technique for intraduodenal administration of drug suspensions/solutions with concurrent pH monitoring applied to ibuprofen formulations

Characterization of dissolution of solid suspended drug particles in vivo is important for developing biopredictive in vitro tests. Therefore, methods to gain deeper insights into particle dissolution in vivo are needed. The soft Bioperm intubation method, a well established tool for investigation of permeability, absorption, metabolism, and drug interactions at predefined locations in the gastroinstinal tract, was modified. The novel intubation method involved pump-controlled infusion of pharmaceutical suspensions as well as simultaneous pH monitoring. This technique was used in a proof of concept study in healthy humans. Plasma sampling and non-compartmental analysis allowed comparison of three different ibuprofen drug products, a solution and two suspensions with different particle size distribution, as well as two different infusion rates. Both a particle size effect and an effect of altering infusion rates on pharmacokinetic parameters were shown. Moreover, it was possible to monitor intestinal pH changes after intestinal infusion. Infusion of ibuprofen resulted in a pH drop that was quantified by the concept of Area Between Curves (ABC).

Will MRI of gastrointestinal function parallel the clinical success of cine cardiac MRI?

Cine cardiac MRI is generally accepted as the "gold-standard" for functional myocardial assessment. It only took a few years after the development of commercial MRI systems for functional cardiac imaging to be developed, with electrocardiogram (ECG)-gated cine imaging first reported in 1988. The function of the gastrointestinal (GI) tract is more complex to study compared to the heart. However, the idea of having a non-invasive tool to study the GI function that also allows the concurrent assessment of different aspects of this function has become more and more attractive in the gastroenterological field. This review summarises key literature of the last 5 years to describe the current status of MRI in respect to the evaluation of GI function, highlighting the gaps and challenges and the future prospects. As the clinical application of a new technique requires that its clinical utility is confirmed by demonstration of its ability to enable clinicians to make a diagnosis and/or predict the treatment response, this review also considers whether or not this has been achieved, and how MRI has been validated against techniques currently recognised as the gold standard in clinical practice.

Individualized in vitro and in silico methods for predicting in vivo performance of enteric-coated tablets containing a narrow therapeutic index drug

The efficacy of narrow therapeutic index (NTI) drugs is closely related to their plasma concentration-time profile. Particularly for these compounds interindividual variability of gastrointestinal (GI) parameters relevant to in vivo drug release may result in fluctuations of the plasma concentration. The present study focused on assessing the influence of individual GI pH- and transit profiles on drug release of enteric valproate tablet formulations by means of individualized in vitro dissolution experiments. After initial experiments simulating GI passages in average healthy adults, a novel in vitro dissolution model was used to simulate individual GI pH- and transit profiles with physiologically relevant dissolution media. Based on the dissolution profiles obtained in these experiments, individual in silico plasma profiles were generated and compared to fasted in vivo data applying a mean Euclidean distance approach. Simulated individual gastric residence time was identified as crucial parameter determining the onset of absorption, whereas the shape of the plasma profile is mainly influenced by individual valproate pharmacokinetics. The novel in vitro and in silico methods used in this study are promising tools for estimating in vivo drug release and plasma concentration in individual subjects and thus may contribute to a prospective risk assessment for NTI formulations.