Measurement of Drug Concentration in the Stomach After Intragastric Administration of Drug Solution to Healthy Volunteers: Analysis of Intragastric Fluid Dynamics and Drug Absorption

More Than a Gut Feeling─A Combination of Physiologically Driven Dissolution and Pharmacokinetic Modeling as a Tool for Understanding Human Gastric Motility

In vivo studies of formulation performance with in vitro and/or in silico simulations are often limited by significant gaps in our knowledge of the interaction between administered dosage forms and the human gastrointestinal tract. This work presents a novel approach for the investigation of gastric motility influence on dosage form performance, by combining biopredictive dissolution tests in an innovative PhysioCell apparatus with mechanistic physiology-based pharmacokinetic modeling. The methodology was based on the pharmacokinetic data from a large (n = 118) cohort of healthy volunteers who ingested a capsule containing a highly soluble and rapidly absorbed drug under fasted conditions. The developed dissolution tests included biorelevant media, varied fluid flows, and mechanical stress events of physiological timing and intensity. The dissolution results were used as inputs for pharmacokinetic modeling that led to the deduction of five patterns of gastric motility and their prevalence in the studied population. As these patterns significantly influenced the observed pharmacokinetic profiles, the proposed methodology is potentially useful to other in vitro-in vivo predictions involving immediate-release oral dosage forms.

Effect of particle size on gastric emptying of enteric-coated granules in fasted beagle dogs: Relationship with interdigestive migrating motor complex

This study investigates the particle size threshold at which the interdigestive migrating motor complex (IMMC) becomes active in gastric emptying for fasted beagle dogs. Enteric-coated granules containing cetirizine dihydrochloride (CET) were prepared in three particle sizes, 200, 660, and 1,200 µm (D50). To mark IMMC timing and water movement from the stomach, enteric-coated aspirin tablets and acetaminophen solution were used. To six fasted beagle dogs with 50 mL of acetaminophen solution was administered each granule size as a multiple-unit and a single enteric-coated aspirin tablet (3-period crossover study). No significant difference in pharmacokinetic parameters of CET after oral administration of different particle sizes was observed. However, the appearance time of CET in plasma with smaller granules (200 and 660 µm) was significantly faster than that of salicylic acid (a major metabolite of aspirin) in all dogs. In the case of the largest granules (1,200 µm), no significant time difference was observed in the appearance of both compounds in plasma. Furthermore, in two dogs, both compounds appeared at the same time, implying IMMC-regulated gastric emptying for the largest CET granules. These results support a particle size threshold between 660 and 1,200 µm for gastric emptying without IMMC action in fasted beagle dogs.

Drug dissolution and transit in a heterogenous gastric chyme after fed administration: Semi-mechanistic modeling and simulations for an immediate-release and orodispersible tablets containing a poorly soluble drug

Mathematical models that treat the fed stomach content as a uniform entity emptied with a constant rate may not suffice to explain pharmacokinetic profiles recorded in clinical trials. In reality, phenomena such as the Magenstrasse or chyme areas of different pH and viscosity, play an important role in the intragastric drug dissolution and its transfer to the intestine. In this study, we investigated the data gathered in the bioequivalence trial between an immediate-release tablet (Reference) and an orally dispersible tablet (Test) with a poorly soluble weak base drug administered with or without water after a high-fat high-calorie breakfast. Maximum concentrations (Cmax) were significantly greater after administering the Reference product than the Test tablets, despite similar in vitro dissolution profiles. To explain this difference, we constructed a novel semi-mechanistic IVIVP model including a heterogeneous gastric chyme. The drug dissolution in vivo was modeled from the in vitro experiments in biorelevant media simulating gastric and intestinal fluids in the fed state (FEDGAS and FeSSIF). The key novelty of the model was separating the stomach contents into two compartments: isolated chyme (the viscous food content) that carries the drug slowly, and aq_chyme open for rapid Magenstrasse-like routes of drug transit. Drug distribution between these two compartments was both formulation- and administration-dependent, and recognized the respective drug fractions from the clinical pharmacokinetic data. The model's assumption about the nonuniform mixing of the API with the chyme, influencing differential drug dissolution and transit kinetics, led to simulating plasma concentration profiles that reflected well the variability observed in the clinical trial. The model indicated that, after administration, the Reference product mixes to a greater extent with aq_chyme, where the released drug dissolves better and transfers faster to the intestine. In conclusion, this novel approach underlines that diverse gastric emptying of different oral dosage forms may significantly impact pharmacokinetics and affect the outcomes of bioequivalence trials.

Forecasting the effect of water gastric emptying patterns on model drug release in an in vitro glass-bead flow-through system

Oral solid dosage forms are most frequently administered with a glass of water which empties from the stomach relatively fast, but with a certain variability in its emptying kinetics. The purpose of this study was thus to simulate different individual water gastric emptying (GE) patterns in an in vitro glass-bead flow-through dissolution system. Further, the effect of GE on the dissolution of model drugs from immediate-release tablets was assessed by determining the amount of dissolved drug in the samples pumped out of the stomach compartment. Additionally, different HCl solutions were used as dissolution media to assess the effect of the variability of pH of the gastric fluid on the dissolution of three model drugs: paracetamol, diclofenac sodium, and dipyridamole. The difference in fast and slow GE kinetics resulted in different dissolution profiles of paracetamol in all studied media. For diclofenac sodium and dipyridamole tablets, the effect of GE kinetics was well observed only in media, where the solubility was not a limiting factor. Therefore, GE kinetics of co-ingested water influences the drug release from immediate-release tablets, however, in certain cases, other parameters influencing drug dissolution can partly or fully hinder the expression of this effect.

Comparison of Non-Covalent and Covalent Interactions between Lactoferrin and Chlorogenic Acid

Adding polyphenols to improve the absorption of functional proteins has become a hot topic. Chlorogenic acid is a natural plant polyphenol with anti-inflammatory, antioxidant, and anticancer properties. Bovine lactoferrin is known for its immunomodulatory, anticancer, antibacterial, and iron-chelating properties. Therefore, the non-covalent binding of chlorogenic acid (CA) and bovine lactoferrin (BLF) with different concentrations under neutral conditions was studied. CA was grafted onto lactoferrin molecules by laccase catalysis, free radical grafting, and alkali treatment. The formation mechanism of non-covalent and covalent complexes of CA-BLF was analyzed by experimental test and theoretical prediction. Compared with the control BLF, the secondary structure of BLF in the non-covalent complex was rearranged and unfolded to provide more active sites, the tertiary structure of the covalent conjugate was changed, and the amino group of the protein participated in the covalent reaction. After adding CA, the covalent conjugates have better functional activity. These lactoferrin-polyphenol couplings can carry various bioactive compounds to create milk-based delivery systems for encapsulation.

An extension of biorelevant fed-state dissolution tests to clinical pharmacokinetics - A study on gastrointestinal factors influencing rivaroxaban exposure and efficacy in atrial fibrillation patients

A direct oral anticoagulant rivaroxaban fails to prevent stroke and systemic embolism in one-to-several percent of patients with nonvalvular atrial fibrillation (NVAF), but the reasons are unknown. The study used semi-mechanistic in vitro-in vivo prediction (IVIVP) modeling to explore the reasons for ineffective thrombosis prevention in NVAF patients. Steady-state drug concentrations in plasma were measured at 0 h (Ctrough), 3 h (C3h), and 12 h post-dosing in thirty-four patients treated with 20 mg rivaroxaban daily. The clinical data were compared against "virtual twins" generated with a novel IVIVP model that combined drug dissolution modeling, mechanistic description of gastric drug transit, and population pharmacokinetics defining the variability of drug disposition. The nonresponders had significantly lower C3h and Ctrough than the responders (p < 0.001) and the covariates included in the population pharmacokinetic submodel did not fully explain this difference. Simulations involving varied gastrointestinal parameters in the "virtual twins" revealed that lower small intestinal effective permeability (Peff), rather than a slower stomach emptying rate, could explain low rivaroxaban exposure in the nonresponders. IVIVP modeling was effectively used for exploring pharmacotherapy failure. Low Peff, found as a major determinant of ineffective rivaroxaban treatment, encourages further research to find (pato)physiological factors influencing suboptimal absorption.

Molecular insight into binding behavior of caffeine with lactoferrin: Spectroscopic, molecular docking, and simulation study

The majority of bioactive substances in the human diet come from polyphenols. Here, we use spectroscopy, molecular docking, molecular dynamics simulations, and in vitro digestion to look at the relationship between caffeine (CAF) and bovine lactoferrin (BLF). The correlation analysis of the CAF-BLF fluorescence quenching process revealed that the reaction was spontaneous and that the CAF-BLF fluorescence quenching process may have been static. The predominant intrinsic binding forces were hydrogen bonds and van der Waals forces, which were also supported by molecular docking and molecular dynamics simulations. Through Fourier infrared and circular dichroism spectroscopy experiments, it was found that CAF changed the secondary structure of BLF and might bind to the hydrophobic amino acids of BLF. Compared with BLF, CAF-BLF showed inhibitory effects on digestion in simulated in vitro digestion. It will be helpful to better understand the interaction between CAF and BLF and provide the basis for the development of innovative dairy products.

Safety of surfactant excipients in oral drug formulations

Surfactants are a diverse group of compounds that share the capacity to adsorb at the boundary between distinct phases of matter. They are used as pharmaceutical excipients, food additives, emulsifiers in cosmetics, and as household/industrial detergents. This review outlines the interaction of surfactant-type excipients present in oral pharmaceutical dosage forms with the intestinal epithelium of the gastrointestinal (GI) tract. Many surfactants permitted for human consumption in oral products reduce intestinal epithelial cell viability in vitro and alter barrier integrity in epithelial cell monolayers, isolated GI tissue mucosae, and in animal models. This suggests a degree of mis-match for predicting safety issues in humans from such models. Recent controversial preclinical research also infers that some widely used emulsifiers used in oral products may be linked to ulcerative colitis, some metabolic disorders, and cancers. We review a wide range of surfactant excipients in oral dosage forms regarding their interactions with the GI tract. Safety data is reviewed across in vitro, ex vivo, pre-clinical animal, and human studies. The factors that may mitigate against some of the potentially abrasive effects of surfactants on GI epithelia observed in pre-clinical studies are summarised. We conclude with a perspective on the overall safety of surfactants in oral pharmaceutical dosage forms, which has relevance for delivery system development.

Facile one-pot multicomponent synthesis of peptoid based gelators as novel scaffolds for drug incorporation and pH-sensitive release

Infections caused by bacteria are the primary cause of illness and death globally, and antibiotics are the most commonly used medications to treat them. However, there are certain inherent problems in administering these drugs without any changes to their effectiveness. In order to sustain the targeted dosage over time, the use of a biocompatible local drug delivery system using low molecular mass gelators is preferred as a potential approach to reduce its side effects. Low molecular weight organic gelators (LMWOGs) have drawn a lot of attention due to their numerous and varied applications in multiple fields. But nowadays its quite a challenging task to synthesize new types of LMWOGs that can fill the significant gap towards potential applications. In this work, we have explored a multicomponent pathway for the synthesis of a small repertoire of peptoids from simple building blocks by a one-pot Ugi reaction. A variety of novel effective low molecular weight organic gelators have been synthesized, leading to the formation of stable self-assembled aggregates in various solvents such as DMSO, aqueous DMSO, and methanol. Consequently, these aggregates give rise to the creation of organogels and organo/hydrogels. The gels have a minimum gelation concentration (MGC) of 1-2% w/v with high thermal stability. Furthermore, successful encapsulation and release of metronidazole (MZ) were achieved within the gel matrix under physiological pH conditions at 37 °C, ensuring the preservation of its structural and functional properties. The results demonstrated that the release rate of MZ from the organo/hydrogels is contingent on pH, exhibiting a gradual and regulated release in mild alkaline environments. Moreover, the devised system displayed noteworthy antimicrobial efficacy against E. coli, underscoring the potential of these novel low molecular weight organic gels (LMWOGs) as effective drug delivery systems in the pharmaceutical industry. The gel formulations exhibit biocompatibility and negligible cytotoxicity, as evidenced by cell viability studies conducted using the MTT assay.

The Effects of Degree and Duration of Supersaturation on In Vivo Absorption Profiles for Highly Permeable Drugs, Dipyridamole and Ketoconazole

The prediction of oral absorption from a supersaturating drug delivery system (SDDS) remains a significant challenge. Here we evaluated the effects of the degree and duration of supersaturation on in vivoabsorption for dipyridamole and ketoconazole. Various dose concentrations of supersaturated suspensions were prepared by a pH shift method, and in vitro dissolution and in vivo absorption profiles were determined. For dipyridamole, the duration of supersaturation decreased with the increase of the dose concentration owing to rapid precipitation. For ketoconazole, the initially constant dissolved concentrations due probably to the liquid-liquid phase separation (LLPS) as a reservoir were observed at high dose concentrations. However, the LLPS did not delay the peak plasma concentration of ketoconazole in rats, indicating that drug molecules were immediately released from the oil phase to the bulk aqueous phase. For both model drugs, the degree of supersaturation, but not the duration of supersaturation, correlated with systemic exposure, indicating quick drug absorption before precipitation. Therefore, the degree of supersaturation is an important parameter compared with the duration of supersaturation for enhancing the in vivo absorption of highly permeable drugs. These findings would help develop a promising SDDS.

Application of a novel PhysioCell apparatus for biopredictive dissolution tests of oral immediate release formulations - a case study workflow for in vitro-in vivo predictions

Biorelevant dissolution tests of oral solid dosage forms open the gate to valid in vitro-in vivo predictions (IVIVP). A recently developed apparatus, PhysioCell, allows mimicking the fluid flow and pressure waves occurring in the human fasted stomach. In this work, we used the PhysioCell to perform IVIVP for vortioxetine immediate-release (IR) tablets: the originator (Brintellix) and generic product candidates (VORTIO). The dissolved drug was monitored in the gastric (StressCell) and intestinal (Collection Vessel) compartments that contained biorelevant media. Simulated intermittent gastric stress at 15 min and 'housekeeping wave' at 30 min increased the dissolution of Brintellix formulations only. A mechanistic model that best described the observations involved the first-order tablet disintegration with a stress-induced enhancement for Brintellix, dissolution of solid particles in the StressCell, and drug transfer to the Collection Vessel. Then, a semi-mechanistic pharmacokinetic model with dissolution parameters as inputs simulated vortioxetine plasma concentrations in healthy volunteers after single and multiple dosing of Brintellix. Despite different dissolution characteristics, VORTIO provided similar concentration profiles to the originator. In conclusion, PhysioCell dissolution tests, combined with semi-mechanistic IVIVP, can be successfully used to develop IR dosage forms exhibiting gastric stress-related effects.

Conjunction of semi-mechanistic in vitro-in vivo modeling and population pharmacokinetics as a tool for virtual bioequivalence analysis - a case study for a BCS class II drug

Virtual bioequivalence trial (VBE) simulations based on (semi)mechanistic in vitro-in vivo (IVIV) modeling have gained a huge interest in the pharmaceutical industry. Sophisticated commercially available software allows modeling variable drug fates in the gastrointestinal tract (GIT). Surprisingly, the between-subject and inter-occasion variability (IOV) of the distribution volumes and clearances are ignored or simplified, despite substantially contributing to varied plasma drug concentrations. The paper describes a novel approach for IVIV-based VBE by using population pharmacokinetics (popPK). The data from two bioequivalence trials with a poorly soluble BCS class II drug were analyzed retrospectively. In the first trial, the test drug product (biobatch 1) did not meet the bioequivalence criteria, but after a reformulation, the second trial succeeded (biobatch 2). The popPK model was developed in the Monolix software (Lixoft SAS, Simulation Plus) based on the originator's plasma concentrations. The modified Noyes-Whitney model was fitted to the results of discriminative biorelevant dissolution tests of the two biobatches and seven other reformulations. Then, the IVIV model was constructed by joining the popPK model with fixed drug disposition parameters, the drug dissolution model, and mechanistic approximation of the GIT transit. It was used to simulate the drug concentrations at different IOV levels of the primary pharmacokinetic parameters and perform the VBE. Estimated VBE success rates for both biobatches well reflected the outcomes of the bioequivalence trials. The predicted 90% confidence intervals for the area under the time-concentration curves were comparable with the observed values, and the 10% IOV allowed the closest approximation to the clinical results. Simulations confirmed that a significantly lower maximum drug concentration for biobatch 1 was responsible for the first clinical trial's failure. In conclusion, the proposed workflow might aid formulation screening in generic drug development.

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

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

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.

Quantitative assessment of disintegration rate is important for predicting the oral absorption of solid dosage forms containing poorly soluble weak base drugs

This study aimed to develop a novel in silico modeling and simulation that considers the disintegration rate in the stomach to predict the in vivo performance of oral solid dosage forms with slow disintegration rates containing poorly soluble weak base drugs. Oxatomide and manidipine hydrochloride were used as model drugs. First, the in vitro disintegration rate and dissolution rate were determined in biorelevant media that simulate the gastrointestinal fluids in fasted humans using a USP apparatus II paddle dissolution tester. Next, the oral absorption of the dosage forms was predicted using the novel simulation model coupled with not only the dissolution rate but also the estimated disintegration rate. As the in vitro disintegration time was 45 min or longer for both drugs in Fasted State Simulated Gastric Fluid, the disintegration rate of these dosage forms was considered slow as immediate release (IR) tablets. While the predicted and observed pharmacokinetic profiles of both drugs were comparable using the new model, the conventional model, which did not consider the disintegration step, underestimated the oral absorption of both drugs. Thus, our novel simulation model coupled with the disintegration rate estimated from in vitro tests is promising for predicting the in vivo performance of oral solid dosage forms with slow disintegration rates containing poorly soluble weak base drugs.

Formulation strategies to improve the efficacy of intestinal permeation enhancers. Adv Drug Deliv Rev 2021;177:113925. [PMID: 34418495 DOI: 10.1016/j.addr.2021.113925]

The use of chemical permeation enhancers (PEs) is the most widely tested approach to improve oral absorption of low permeability active agents, as represented by peptides. Several hundred PEs increase intestinal permeability in preclinical bioassays, yet few have progressed to clinical testing and, of those, only incremental increases in oral bioavailability (BA) have been observed. Still, average BA values of ~1% were sufficient for two recent FDA approvals of semaglutide and octreotide oral formulations. PEs are typically screened in static in vitro and ex-vivo models where co-presentation of active agent and PE in high concentrations allows the PE to alter barrier integrity with sufficient contact time to promote flux across the intestinal epithelium. The capacity to maintain high concentrations of co-presented agents at the epithelium is not reached by standard oral dosage forms in the upper GI tract in vivo due to dilution, interference from luminal components, fast intestinal transit, and possible absorption of the PE per se. The PE-based formulations that have been assessed in clinical trials in either immediate-release or enteric-coated solid dosage forms produce low and variable oral BA due to these uncontrollable physiological factors. For PEs to appreciably increase intestinal permeability from oral dosage forms in vivo, strategies must facilitate co-presentation of PE and active agent at the epithelium for a sustained period at the required concentrations. Focusing on peptides as examples of a macromolecule class, we review physiological impediments to optimal luminal presentation, discuss the efficacy of current PE-based oral dosage forms, and suggest strategies that might be used to improve them.

Towards virtual bioequivalence studies for oral dosage forms containing poorly water-soluble drugs: a physiologically based biopharmaceutics modeling (PBBM) approach

The objective of the present study was to develop a physiologically based biopharmaceutics (PBBM) approach to predict the bioequivalence of dosage forms containing poorly soluble drugs. Aripiprazole and enzalutamide were used as model drugs. Variations in the gastrointestinal (GI) physiological parameters of fasted humans were taken into consideration in in vitro biorelevant dissolution testing and in an in silico PBBM simulations. To estimate bioequivalence between dosage forms, the inter-individual variabilities in their performance in virtual human subjects were predicted from the in vitro studies and variability in e.g. gastric emptying and fluid volume in the stomach was also taken into account. Formulations with different in vitro dissolution performance, a solution and a tablet formulation, were used in order to evaluate the accuracy of bioequivalence prediction using the PBBM approach. The bioequivalence parameters, i.e. geometric mean ratio and 90% confidence interval, for both drugs were predicted well in the virtual studies. In order to achieve even more precise predictions, it will be important to continue characterizing GI physiological parameters, along with their variabilities, on both an inter-subject and inter-occasion basis.

Bioequivalence of Oral Drug Products in the Healthy and Special Populations: Assessment and Prediction Using a Newly Developed In Vitro System "BE Checker"

In order to assess and predict the bioequivalence (BE) of oral drug products, a new in vitro system "BE checker" was developed, which reproduced the environmental changes in the gastrointestinal (GI) tract by changing the pH, composition, and volume of the medium in a single chamber. The dissolution and membrane permeation profiles of drugs from marketed products were observed in the BE checker under various conditions reflecting the inter-patient variations of the GI physiology. As variable factors, initial gastric pH, gastric emptying time, and GI agitation strength were varied in vitro. Dipyridamole, a basic drug, showed rapid and supersaturated dissolution when the paddle speed in the donor chamber was 200 rpm, which corresponds to the high agitation strength in the stomach. In contrast, supersaturated dissolution disappeared, and the permeated amount decreased under the conditions with a slow paddle speed (100 and 50 rpm) and short gastric emptying time (10 min). In those conditions, disintegration of the formulation was delayed, and the subsequent dissolution of dipyridamole was not completed before the fluid pH was changed to neutral. Similar results were obtained when the initial gastric pH was increased to 3.0, 5.0, and 6.5. To investigate that those factors also affect the BE of oral drug products, dissolution and permeation of naftopidil from its ordinary and orally disintegrating (OD) tablets were observed in the BE checker. Both products showed the similar dissolution profiles when the paddle speed and gastric emptying time were set to 100 rpm and 10 or 20 min, respectively. However, at a low paddle speed (50 rpm), the dissolution of naftopidil from ordinary tablets was slower than that from the OD tablets, and the permeation profiles became dissimilar. These results indicated the possibility of the bioinequivalence of some oral formulations in special patients whose GI physiologies are different from those in the healthy subjects. The BE checker can be a highly capable in vitro tool to assess the BE of oral drug products in various populations.

In Vitro Analysis of N-Nitrosodimethylamine (NDMA) Formation From Ranitidine Under Simulated Gastrointestinal Conditions

Importance

A publication reported that N-nitrosodimethylamine (NDMA), a probable human carcinogen, was formed when ranitidine and nitrite were added to simulated gastric fluid. However, the nitrite concentrations used were greater than the range detected in acidic gastric fluid in prior clinical studies.

Objective

To characterize NDMA formation following the addition of ranitidine to simulated gastric fluid using combinations of fluid volume, pH levels, and nitrite concentrations, including physiologic levels.

Design, Setting, and Participants

One 150-mg ranitidine tablet was added to 50 or 250 mL of simulated gastric fluid with a range of nitrite concentrations from the upper range of physiologic (100 μmol/L) to higher concentrations (10 000 μmol/L) with a range of pH levels. NDMA amounts were assessed with a liquid chromatography-mass spectrometry method.

Main Outcomes and Measures

NDMA detected in simulated gastric fluid 2 hours after adding ranitidine.

Results

At a supraphysiologic nitrite concentration (ie, 10 000 μmol/L), the mean (SD) amount of NDMA detected in 50 mL simulated gastric fluid 2 hours after adding ranitidine increased from 222 (12) ng at pH 5 to 11 822 (434) ng at pH 1.2. Subsequent experiments with 50 mL of simulated gastric fluid at pH 1.2 with no added nitrite detected a mean (SD) of 22 (2) ng of NDMA, which is the background amount present in the ranitidine tablets. Similarly, at the upper range of physiologic nitrite (ie, 100 μmol/L) or at nitrite concentrations as much as 50-fold greater (1000 or 5000 μmol/L) only background mean (SD) amounts of NDMA were observed (21 [3] ng, 24 [2] ng, or 24 [3] ng, respectively). With 250 mL of simulated gastric fluid, no NDMA was detected at the upper physiologic range (100 μmol/L) or 10-fold physiologic (1000 μmol/L) nitrite concentrations, while NDMA was detected (mean [SD] level, 7353 [183] ng) at a 50-fold physiologic nitrite concentration (5000 μmol/L).

Conclusions and Relevance

In this in vitro study of ranitidine tablets added to simulated gastric fluid with different nitrite concentrations, ranitidine conversion to NDMA was not detected until nitrite was 5000 μmol/L, which is 50-fold greater than the upper range of physiologic gastric nitrite concentrations at acidic pH. These findings suggest that ranitidine is not converted to NDMA in gastric fluid at physiologic conditions.

Evaluating the Impact of Physiological Properties of the Gastrointestinal Tract On Drug In Vivo Performance Using Physiologically Based Biopharmaceutics Modeling and Virtual Clinical Trials

The physiological properties of the gastrointestinal tract, such as pH, fluid volume, bile salt concentration, and gastrointestinal transit time, are highly variable in vivo. These properties can affect the dissolution and absorption of a drug, depending on its properties and formulation. The effect of gastrointestinal physiology on the bioperformance of a drug was studied in silico for a delayed-release pantoprazole tablet and an immediate-release dolutegravir tablet. Physiologically based absorption models were developed and virtual clinical trials were performed. Reasons for the variability in drug bioperformance between subjects were investigated, taking into account differences in gastrointestinal tract characteristics, pharmacokinetic parameters, and additional parameters (e.g., permeability). Default software parameters describing gastrointestinal physiology in the fasted and fed states, and variation in these parameters, were altered to match variability in these parameters reported in vivo. The altered model physiologies better described the variability of gastrointestinal conditions, and therefore the results of virtual trials using these physiologies are likely to be more relevant in vivo. With such altered gastrointestinal physiologies used to develop models, it is possible to obtain additional knowledge and improve the understanding of subject-formulation interactions.

In Vitro Sensitivity Analysis of the Gastrointestinal Dissolution Profile of Weakly Basic Drugs in the Stomach-to-Intestine Fluid Changing System: Explanation for Variable Plasma Exposure after Oral Administration

An in vitro methodology for simulating the change in the pH and composition of gastrointestinal fluid associated with the transition of orally administered drugs from the stomach to the small intestine was developed (the stomach-to-intestine fluid changing system (the SIFC system)). This system was applied to in vitro sensitivity analysis on the dissolution of weakly basic drugs, and the obtained results were discussed in relation to the intrasubject variability in the plasma exposure in human bioequivalence (BE) study. Three types of protocols were employed (steep pH change: pH 1.6 FaSSGF → pH 6.5 FaSSIF, gradual pH change: pH 1.6 FaSSGF → pH 6.5 FaSSIF, and high gastric pH: pH 4.0 FaSSGF → pH 6.5 FaSSIF). Regardless of the protocols and the forms of drug applied in active pharmaceutical ingredient powder or formulation, dissolution profiles of pioglitazone after fluid shift were similar and the final concentrations in FaSSIF were approximately equal to the saturation solubility in FaSSIF, supporting its small intrasubject variance in human BE study. In contrast, dissolved concentration of terbinafine in the SIFC system became less than half in the high gastric pH protocol than that in other protocols, suggesting the fluctuation of gastric pH as one of the factors of high intrasubject variance of terbinafine in human. Plasma exposure of telmisartan was highly variable especially at the high dose. Although the dissolution of telmisartan in the SIFC system was greatly improved by formulation, it considerably fluctuated during fluid shift especially at the high dose, which corresponds well to in vivo results.

Utilization of Diluted Compendial Media as Dissolution Test Solutions with Low Buffer Capacity for the Investigation of Dissolution Rate of Highly Soluble Immediate Release Drug Products

Research from the past decade has shown that the buffer capacities of intestinal fluids are much lower than those in the media used for dissolution test of many solid formulations. The purpose of this study was to elucidate the effect of buffer capacity on the dissolution profiles of highly soluble drug products, using metoclopramide (a biopharmaceutics classification system [BCS] class III drug) tablets as a model. The dissolution profiles of three metoclopramide products were obtained in Japanese pharmacopeia dissolution medium (pH 1.2 and 6.8), diluted medium with low buffer capacity comparable to that of gastrointestinal fluid, and other biorelevant media. One product showed slower dissolution in the medium with lower buffer capacity (bio-relevant, diluted compendial solution), but substantially similar dissolution in the compendial test solutions. Disintegration difference was implied to be involved in the different dissolution profiles depending on the medium buffer capacity. This study indicated the importance of media buffer capacity as a factor inducing different dissolution between products of highly soluble active pharmaceutical ingredients. The diluted compendial media would be a useful alternative to biorelevant media for the detection of the different formulation performances depending on the buffer capacities.

Automated small-scale in vitro transfer model as screening tool for the prediction of in vivo-dissolution and precipitation of poorly solubles

Precipitation testing, especially for weakly basic APIs, represents a key parameter in drug substance characterization during early development stages, where the amount of API available is limited. Therefore, it was the aim of this study to develop an automated small-scale in vitro transfer model to characterize the supersaturation and precipitation behavior of two poorly water-soluble drugs. Following automation and scale-down of the standard transfer model, the developed small-scale model was used to assess the impact of gastrointestinal variability, i.e. gastric pH, gastric emptying, and gastrointestinal fluid volumes, on supersaturation and precipitation of two weakly basic model compounds, ketoconazole and a new chemical entity from the research laboratories of Merck KGaA, MSC-A. The experiments revealed that variations in gastrointestinal parameters affected the in vitro behavior of ketoconazole, but not of MSC-A. Elevated gastric pH, as it can result from co-medication with acid-reducing drugs, resulted in lower degrees of supersaturation for both substances. This result is in agreement with the observation that the oral bioavailability of ketoconazole is lowered when proton pump inhibitors are co-administered. The small-scale transfer model presented herein represents a valuable in vitro tool to assess the risk of drug precipitation, additionally covering a broad range of gastrointestinal parameters.

Oral Contraceptives after Bariatric Surgery

OBJECTIVE

Bariatric surgery offers a highly effective mode of treatment for obese patients. Some procedures such as bypass cause an alteration in normal gastrointestinal tract with possible consequences for the uptake of orally administered drugs.

METHODS

We assessed the literature to ascertain whether the use of oral drugs and especially oral contraceptives is effective and adequate after bariatric surgery.

RESULTS

The bioavailability of drugs could be affected by the solubility and pH of the modified medium after bariatric surgery and by the loss of gastrointestinal transporters. Bariatric surgery could potentially result in a transient change in the absorption of drugs such as analgesics, antibiotics, antiarrhythmics, anticoagulants, psychotropic, and oral contraceptive drugs. Effective contraception is especially critical in the postoperative period, and implants might be representing a safe contraceptive method in women undergoing bariatric surgery.

CONCLUSION

Each drug will have to be evaluated with respect to its site of absorption and its mechanism of absorption, with special attention on parameters influencing the effectiveness of the absorption processes.

Effects of gastric pH on oral drug absorption: In vitro assessment using a dissolution/permeation system reflecting the gastric dissolution process

The aim of the present study was to evaluate the effects of gastric pH on the oral absorption of poorly water-soluble drugs using an in vitro system. A dissolution/permeation system (D/P system) equipped with a Caco-2 cell monolayer was used as the in vitro system to evaluate oral drug absorption, while a small vessel filled with simulated gastric fluid (SGF) was used to reflect the gastric dissolution phase. After applying drugs in their solid forms to SGF, SGF solution containing a 1/100 clinical dose of each drug was mixed with the apical solution of the D/P system, which was changed to fasted state-simulated intestinal fluid. Dissolved and permeated amounts on applied amount of drugs were then monitored for 2h. Similar experiments were performed using the same drugs, but without the gastric phase. Oral absorption with or without the gastric phase was predicted in humans based on the amount of the drug that permeated in the D/P system, assuming that the system without the gastric phase reflected human absorption with an elevated gastric pH. The dissolved amounts of basic drugs with poor water solubility, namely albendazole, dipyridamole, and ketoconazole, in the apical solution and their permeation across a Caco-2 cell monolayer were significantly enhanced when the gastric dissolution process was reflected due to the physicochemical properties of basic drugs. These amounts resulted in the prediction of higher oral absorption with normal gastric pH than with high gastric pH. On the other hand, when diclofenac sodium, the salt form of an acidic drug, was applied to the D/P system with the gastric phase, its dissolved and permeated amounts were significantly lower than those without the gastric phase. However, the oral absorption of diclofenac was predicted to be complete (96-98%) irrespective of gastric pH because the permeated amounts of diclofenac under both conditions were sufficiently high to achieve complete absorption. These estimations of the effects of gastric pH on the oral absorption of poorly water-soluble drugs were consistent with observations in humans. In conclusion, the D/P system with the gastric phase may be a useful tool for better predicting the oral absorption of poorly water-soluble basic drugs. In addition, the effects of gastric pH on the oral absorption of poorly water-soluble drugs may be evaluated by the D/P system with and without the gastric phase.

Direct In Vivo Human Intestinal Permeability (Peff ) Determined with Different Clinical Perfusion and Intubation Methods

Regional in vivo human intestinal effective permeability (Peff ) is calculated by measuring the disappearance rate of substances during intestinal perfusion. Peff is the most relevant parameter in the prediction of rate and extent of drug absorption from all parts of the intestine. Today, human intestinal perfusions are not performed on a routine basis in drug development. Therefore, it would be beneficial to increase the accuracy of the in vitro and in silico tools used to evaluate the intestinal Peff of novel drugs. This review compiles historical Peff data from 273 individual measurements of 80 substances from 61 studies performed in all parts of the human intestinal tract. These substances include: drugs, monosaccharaides, amino acids, dipeptides, vitamins, steroids, bile acids, ions, fatty acids, and water. The review also discusses the determination and prediction of Peff using in vitro and in silico methods such as quantitative structure-activity relationship, Caco-2, Ussing chamber, animal intestinal perfusion, and physiologically based pharmacokinetic (PBPK) modeling. Finally, we briefly outline how to acquire accurate human intestinal Peff data by deconvolution of plasma concentration-time profiles following regional intestinal bolus dosing.

Encapsulation of sorbitan ester-based organogels in alginate microparticles

Leaching of the internal apolar phase from the biopolymeric microparticles during storage is a great concern as it undoes the beneficial effects of encapsulation. In this paper, a novel formulation was prepared by encapsulating the sunflower oil-based organogels in alginate microparticles. Salicylic acid and metronidazole were used as the model drugs. The microparticles were prepared by double emulsion methodology. Physico-chemical characterization of the microparticles was done by microscopy, FTIR, XRD, and DSC studies. Oil leaching studies, biocompatibility, mucoadhesivity, in vitro drug release, and the antimicrobial efficiency of the microparticles were also performed. The microparticles were found to be spherical in shape. Gelation of the sunflower oil prevented leaching of the internal phase from the microparticles. Release of drugs from the microparticles followed Fickian kinetics and non-Fickian kinetics in gastric and intestinal environments, respectively. Microparticles showed good antimicrobial activity against both Gram-positive (Bacillus subtilis) and Gram-negative (Escherichia coli) bacteria. The results suggested that the developed formulations hold promise to carry oils without leakage of the internal phase. Encapsulation of organogels within the microparticles has improved the drug entrapment efficiency and improved characteristics for controlled delivery applications.

Evaluation of a three compartment in vitro gastrointestinal simulator dissolution apparatus to predict in vivo dissolution

In vitro dissolution tests are performed for new formulations to evaluate in vivo performance, which is affected by the change of gastrointestinal (GI) physiology, in the GI tract. Thus, those environmental changes should be introduced to an in vitro dissolution test. Many studies have successfully shown the improvement of in vitro-in vivo correlations (IVIVC) by introducing those physiological changes into dissolution tests. The gastrointestinal simulator (GIS), a multicompartment in vitro dissolution apparatus, was developed to evaluate in vivo drug dissolution. A gastric-emptying rate along with transit rate are key factors to evaluate in vivo drug dissolution and, hence, drug absorption. Dissolution tests with the GIS were performed with Biopharmaceutical Classification System class I drugs at five different gastric-emptying rates in the fasted state. Computational models were used to determine in vivo gastric-emptying time for propranolol and metoprolol based on the GIS dissolution results. Those were compared with published clinical data to determine the gastric half-emptying time. In conclusion, the GIS is a practical tool to assess dissolution properties and can improve IVIVC.

Quantification of gastrointestinal liquid volumes and distribution following a 240 mL dose of water in the fasted state

The rate and extent of drug dissolution and absorption from solid oral dosage forms is highly dependent upon the volumes and distribution of gastric and small intestinal water. However, little is known about the time courses and distribution of water volumes in vivo in an undisturbed gut. Previous imaging studies offered a snapshot of water distribution in fasted humans and showed that water in the small intestine is distributed in small pockets. This study aimed to quantify the volume and number of water pockets in the upper gut of fasted healthy humans following ingestion of a glass of water (240 mL, as recommended for bioavailability/bioequivalence (BA/BE) studies), using recently validated noninvasive magnetic resonance imaging (MRI) methods. Twelve healthy volunteers underwent upper and lower abdominal MRI scans before drinking 240 mL (8 fluid ounces) of water. After ingesting the water, they were scanned at intervals for 2 h. The drink volume, inclusion criteria, and fasting conditions matched the international standards for BA/BE testing in healthy volunteers. The images were processed for gastric and intestinal total water volumes and for the number and volume of separate intestinal water pockets larger than 0.5 mL. The fasted stomach contained 35 ± 7 mL (mean ± SEM) of resting water. Upon drinking, the gastric fluid rose to 242 ± 9 mL. The gastric water volume declined rapidly after that with a half emptying time (T50%) of 13 ± 1 min. The mean gastric volume returned back to baseline 45 min after the drink. The fasted small bowel contained a total volume of 43 ± 14 mL of resting water. Twelve minutes after ingestion of water, small bowel water content rose to a maximum value of 94 ± 24 mL contained within 15 ± 2 pockets of 6 ± 2 mL each. At 45 min, when the glass of water had emptied completely from the stomach, total intestinal water volume was 77 ± 15 mL distributed into 16 ± 3 pockets of 5 ± 1 mL each. MRI provided unprecedented insights into the time course, number, volume, and location of water pockets in the stomach and small intestine under conditions that represent standard BA/BE studies using validated techniques. These data add to our current understanding of gastrointestinal physiology and will help improve physiological relevance of in vitro testing methods and in silico transport analyses for prediction of bioperformance of oral solid dosage forms, particularly for low solubility Biopharmaceutics Classification System (BCS) Class 2 and Class 4 compounds.

Human in vivo regional intestinal permeability: importance for pharmaceutical drug development

Both the development and regulation of pharmaceutical dosage forms have undergone significant improvements and development over the past 25 years, due primarily to the extensive application of the biopharmaceutical classification system (BCS). The Biopharmaceutics Drug Disposition Classification System, which was published in 2005, has also been a useful resource for predicting the influence of transporters in several pharmacokinetic processes. However, there remains a need for the pharmaceutical industry to develop reliable in vitro/in vivo correlations and in silico methods for predicting the rate and extent of complex gastrointestinal (GI) absorption, the bioavailability, and the plasma concentration-time curves for orally administered drug products. Accordingly, a more rational approach is required, one in which high quality in vitro or in silico characterizations of active pharmaceutical ingredients and formulations are integrated into physiologically based in silico biopharmaceutics models to capture the full complexity of GI drug absorption. The need for better understanding of the in vivo GI process has recently become evident after an unsuccessful attempt to predict the GI absorption of BCS class II and IV drugs. Reliable data on the in vivo permeability of the human intestine (Peff) from various intestinal regions is recognized as one of the key biopharmaceutical requirements when developing in silico GI biopharmaceutics models with improved predictive accuracy. The Peff values for human jejunum and ileum, based on historical open, single-pass, perfusion studies are presented in this review. The main objective of this review is to summarize and discuss the relevance and current status of these human in vivo regional intestinal permeability values.

Quantitative prediction of formulation-specific food effects and their population variability from in vitro data with the physiologically-based ADAM model: a case study using the BCS/BDDCS Class II drug nifedipine

Quantitative prediction of food effects (FE) upon drug pharmacokinetics, including population variability, in advance of human trials may help with trial design by optimising the number of subjects and sampling times when a clinical study is warranted or by negating the need for conduct of clinical studies. Classification and rule-based systems such as the BCS and BDDCS and statistical QSARs are widely used to anticipate the nature of FE in early drug development. However, their qualitative rather than quantitative nature makes them less appropriate for assessing the magnitude of FE. Moreover, these approaches are based upon drug properties alone and are not appropriate for estimating potential formulation-specific FE on modified or controlled release products. In contrast, physiologically-based mechanistic models can consider the scope and interplay of a range of physiological changes after food intake and, in combination with appropriate in vitro drug- and formulation-specific data, can make quantitative predictions of formulation-specific FE including the inter-individual variability of such effects. Herein the Advanced Dissolution, Absorption and Metabolism (ADAM) model is applied to the prediction of formulation-specific FE for BCS/BDDCS Class II drug and CYP3A4 substrate nifedipine using as far as possible only in vitro data. Predicted plasma concentration profiles of all three studied formulations under fasted and fed states are within 2-fold of clinically observed profiles. The % prediction error (%PE) in fed-to-fasted ratio of Cmax and AUC were less than 5% for all formulations except for the Cmax of Nifedicron (%PE=-29.6%). This successful case study should help to improve confidence in the use of mechanistic physiologically-based models coupled with in vitro data for the anticipation of FE in advance of in vivo studies. However, it is acknowledged that further studies with drugs/formulations exhibiting a wide range of properties are required to further validate this methodology.