Physiologically Based Biopharmaceutics Model (PBBM) of Minimally Absorbed Locally Acting Drugs in the Gastrointestinal Tract-Case Study: Tenapanor.

A physiologically based biopharmaceutics model (PBBM) was developed to predict stool and urine sodium content in response to tenapanor administration in healthy subjects. Tenapanor is a minimally absorbed small molecule that inhibits the sodium/hydrogen isoform 3 exchanger (NHE3). It is used to treat irritable bowel syndrome with constipation (IBS-C). Its mode of action in the gastrointestinal tract reduces the uptake of sodium, resulting in an increase in water secretion in the intestinal lumen and accelerating intestinal transit time. The strategy employed was to perform drug-drug interaction (DDI) modelling between sodium and tenapanor, with sodium as the "victim" administered as part of daily food intake and tenapanor as the "perpetrator" altering sodium absorption. Food effect was modelled, including meal-induced NHE3 activity using sodium as an inducer by normalising the induction kinetics of butyrate to sodium equivalents. The presented model successfully predicted both urine and stool sodium content in response to tenapanor dosed in healthy subjects (within 1.25-fold error) and provided insight into the clinical observations of tenapanor dosing time relative to meal ingestion. The PBBM model was applied retrospectively to assess the impact of different forms of tenapanor (free base vs. HCl salt) on its pharmacodynamic (PD) effect. The developed modelling strategy can be effectively adopted to increase confidence in using PBBM models for the prediction of the in vivo behaviour of minimally absorbed, locally acting drugs in the gastrointestinal tract, when other approaches (e.g., biomarkers or PD data) are not available.

Usefulness of the Beagle Model in the Evaluation of Paracetamol and Ibuprofen Exposure after Oral Administration to Pediatric Populations: An Exploratory Study.

The present study aimed to explore the usefulness of beagle dogs in combination with physiologically based pharmacokinetic (PBPK) modeling in the evaluation of drug exposure after oral administration to pediatric populations at an early stage of pharmaceutical product development. An exploratory, single-dose, crossover bioavailability study in six beagles was performed. A paracetamol suspension and an ibuprofen suspension were coadministered in the fasted-state conditions, under reference-meal fed-state conditions, and under infant-formula fed-state conditions. PBPK models developed with GastroPlus v9.7 were used to inform the extrapolation of beagle data to human infants and children. Beagle-based simulation outcomes were compared with published human-adult-based simulations. For paracetamol, fasted-state conditions and reference-meal fed-state conditions in beagles appeared to provide adequate information for the applied scaling approach. Fasted-state and/or reference-meal fed-state conditions in beagles appeared suitable to simulate the performance of ibuprofen suspension in pediatric populations. Contrary to human-adult-based translations, extrapolations based on beagle data collected under infant-formula fed-state conditions appeared less useful for informing simulations of plasma levels in pediatric populations. Beagle data collected under fasted and/or reference-meal fed-state conditions appeared to be useful in the investigation of pediatric product performance of the two investigated highly permeable and highly soluble drugs in the upper small intestine. The suitability of the beagle as a preclinical model to understand pediatric drug product performance under different dosing conditions deserves further evaluation with a broader spectrum of drugs and drug products and comparisons with pediatric in vivo data.

A review of paediatric injectable drug delivery to inform the study of product acceptability - An introduction.

AIM: The EMA defines acceptability as "the overall ability and willingness of the patient to use, and their caregiver to administer, the medicine as intended" [1]. This paper seeks to outline issues of acceptability in relation to injectable therapy, namely intravenous (IV), intramuscular (IM) and subcutaneous (SC) administration routes, and to lay a foundation to identify a minimum set of data that would satisfy Regulatory Authorities when discussing the acceptability of an injectable product. In addition, it will alert drug product developers to other factors that might contribute to good practice, alternative administration strategies and overall adherence to achieve successful treatment. Whilst the term 'parenteral' means "outside the intestine" [2,3] and so potentially covers a range of administration routes including intranasal and percutaneous administration, this review focuses on IV, IM and SC administration by injection. The use of indwelling canulae or catheters to reduce venepuncture and facilitate prolonged treatment is common and may impact acceptability [4]. This may be influenced by information provided by the manufacturer but is not always in their direct control. Other injectable products suitable for routes such as intradermal, intra-articular, intraosseous and intrathecal, share the requirement to be acceptable but are not specifically covered in this paper [2,5].

The association between anticholinergic burden and mobility: a systematic review and meta-analyses.

BACKGROUND: As people age, they accumulate several health conditions, requiring the use of multiple medications (polypharmacy) to treat them. One of the challenges with polypharmacy is the associated increase in anticholinergic exposure to older adults. In addition, several studies suggest an association between anticholinergic burden and declining physical function in older adults. OBJECTIVE/PURPOSE: This systematic review aimed to synthesise data from published studies regarding the association between anticholinergic burden and mobility. The studies were critically appraised for the strength of their evidence. METHODS: A systematic literature search was conducted across five electronic databases, EMBASE, CINAHL, PSYCHINFO, Cochrane CENTRAL and MEDLINE, from inception to December 2021, to identify studies on the association of anticholinergic burden with mobility. The search was performed following a strategy that converted concepts in the PECO elements into search terms, focusing on terms most likely to be found in the title and abstracts of the studies. For observational studies, the risk of bias was assessed using the Newcastle Ottawa Scale, and the Cochrane risk of bias tool was used for randomised trials. The GRADE criteria was used to rate confidence in evidence and conclusions. For the meta-analyses, we explored the heterogeneity using the Q test and I2 test and the publication bias using the funnel plot and Egger's regression test. The meta-analyses were performed using Jeffreys's Amazing Statistics Program (JASP). RESULTS: Sixteen studies satisfied the inclusion criteria from an initial 496 studies. Fifteen studies identified a significant negative association of anticholinergic burden with mobility measures. One study did not find an association between anticholinergic intervention and mobility measures. Five studies included in the meta-analyses showed that anticholinergic burden significantly decreased walking speed (0.079 m/s ± 0.035 MD ± SE,95% CI: 0.010 to 0.149, p = 0.026), whilst a meta-analysis of four studies showed that anticholinergic burden significantly decreased physical function as measured by three variations of the Instrumental Activities of Daily Living (IADL) instrument 0.27 ± 0.12 (SMD ± SE,95% CI: 0.03 to 0.52), p = 0.027. The results of both meta-analyses had an I2 statistic of 99% for study heterogeneity. Egger's test did not reveal publication bias. CONCLUSION: There is consensus in published literature suggesting a clear association between anticholinergic burden and mobility. Consideration of cognitive anticholinergic effects may be important in interpreting results regarding the association of anticholinergic burden and mobility as anticholinergic drugs may affect mobility through cognitive effects.

Understanding the Impact of Age-Related Changes in Pediatric GI Solubility by Multivariate Data Analysis.

The aim of this study was to understand drug solubilization as a function of age and identify drugs at risk of altered drug solubility in newborns and young infants in comparison to adults. Multivariate statistical analysis was used to understand drug solubilization as a function of drug's physicochemical properties and the composition of gastrointestinal fluids. The solubility of seven poorly soluble compounds was assessed in adult and age-specific fasted and fed state biorelevant media. Partial least squares regression (PLS-R) was used to assess the influence of (i) drug physicochemical properties and (ii) age-related changes in simulated GI fluids, as well as (iii) their interactions, on the pediatrics-to-adult solubility ratio (Sp/Sa (%)). For five out of seven of the compounds investigated, Sp/Sa (%) values fell outside of the 80-125% limits in at least one of the pediatric media. Lipophilicity was responsible for driving drug solubility differences between adults and children in all the biorelevant media investigated, while drug ionization was most relevant in the fed gastric media, and the fasted/fed intestinal media. The concentration of bile salts and lecithin in the fasted and fed intestinal media was critical in influencing drug solubility, while food composition (i.e., cow's milk formula vs. soy formula) was a critical parameter in the fed gastric state. Changes in GI fluid composition between younger pediatric patients and adults can significantly alter drug luminal solubility. The use of pediatric biorelevant media can be helpful to identify the risk of altered drug solubilization in younger patients during drug development.

Performance Evaluation of Montelukast Pediatric Formulations: Part I-Age-Related In Vitro Conditions.

This study aimed to explore the potential of biopharmaceutics in vitro tools to predict drug product performance in the pediatric population. Biorelevant dissolution set-ups were used to predict how age and medicine administration practices affect the in vitro dissolution of oral formulations of a poorly water-soluble compound, montelukast. Biorelevant age-appropriate dissolution studies of Singulair® (granules and chewable tablets) were conducted with the µDISS profiler™, USP 4 apparatus, USP 2 apparatus, and mini-paddle apparatus. Biorelevant simulating fluids representative of adult and pediatric conditions were used in the dissolution studies. The biorelevant dissolution conditions were appropriately selected (i.e. volumes, transit times, etc.) to mimic the gastrointestinal conditions of each of the subpopulations tested. Partial least squares regression (PLS-R) was performed to understand the impact of in vitro variables on the dissolution of montelukast. Montelukast dissolution was significantly affected by the in vitro hydrodynamics used to perform the dissolution tests (µDISS profiler™: positive effect); choice of simulation of gastric (negative effect) and/or intestinal conditions (positive effect) of the gastrointestinal tract; and simulation of prandial state (fasted state: negative effect, fed state: positive effect). Age-related biorelevant dissolution of Singulair® granules predicted the in vivo effect of the co-administration of the formulation with applesauce and formula in infants. This study demonstrates that age-appropriate biorelevant dissolution testing can be a valuable tool for the assessment of drug performance in the pediatric population.

Performance Evaluation of Montelukast Pediatric Formulations: Part II - a PBPK Modelling Approach.

This study aimed to build a physiologically based pharmacokinetic (PBPK) model coupled with age-appropriate in vitro dissolution data to describe drug performance in adults and pediatric patients. Montelukast sodium was chosen as a model drug. Two case studies were investigated: case study 1 focused on the description of formulation performance from adults to children; case study 2 focused on the description of the impact of medicine co-administration with vehicles on drug exposure in infants. The PBPK model for adults and pediatric patients was developed in Simcyp® v18.2 informed by age-appropriate in vitro dissolution results obtained in a previous study. Oral administration of montelukast was simulated with the ADAM™ model. For case study 1, the developed PBPK model accurately described montelukast exposure in adults and children populations after the administration of montelukast chewable tablets. Two-stage dissolution testing in simulated fasted gastric to intestinal conditions resulted in the best description of in vivo drug performance in adults and children. For case study 2, a good description of in vivo drug performance in infants after medicine co-administration with vehicles was achieved by incorporating in vitro drug dissolution (under simulated fasted gastric to fed intestinal conditions) into a fed state PBPK model with consideration of the in vivo dosing conditions (mixing of formulation with applesauce or formula). The case studies presented demonstrate how a PBPK absorption modelling strategy can facilitate the description of drug performance in the pediatric population to support decision-making and biopharmaceutics understanding during pediatric drug development.

Oral administration of buparvaquone nanostructured lipid carrier enables in vivo activity against Leishmania infantum.

Leishmaniasis, a neglected tropical disease, is prevalent in 98 countries with the occurrence of 1.3 million new cases annually. The conventional therapy for visceral leishmaniasis requires hospitalization due to the severe adverse effects of the drugs, which are administered parenterally. Buparvaquone (BPQ) showed in vitro activity against leishmania parasites; nevertheless, it has failed in vivo tests due to its low aqueous solubility. Though, lipid nanoparticles can overcome this holdback. In this study we tested the hypothesis whether BPQ-NLC shows in vivo activity against L. infantum. Two optimized formulations were prepared (V1: 173.9 ± 1.6 nm, 0.5 mg of BPQ/mL; V2: 232.4 ± 1.6 nm, 1.3 mg of BPQ/mL), both showed increased solubility up to 73.00-fold, and dissolution up to 83.29%, while for the free drug it was only 2.89%. Cytotoxicity test showed their biocompatibility (CC50 >554.4 µM). Besides, the V1 dose of 0.3 mg/kg/day for 10 days reduced the parasite burden in 83.4% ±18.2% (p <0.05) in the liver. BPQ-NLC showed similar leishmanicidal activity compared to miltefosine. Therefore, BPQ-NLC is a promising addition to the limited therapeutic arsenal suitable for leishmaniasis oral administration treatment.

Evaluating pediatric and adult simulated fluids solubility: Abraham solvation parameters and multivariate analysis.

PURPOSE: To understand drug solubilization as a function of age and identify drugs at risk of altered drug solubility in pediatric patients. To assess the discrimination ability of the Abraham solvation parameters and age-related changes in simulated media composition to predict in vitro drug solubility differences between pediatric and adult gastrointestinal conditions by multivariate data analysis. METHODS: Differences between drug solubility in pediatric and adult biorelevant media were expressed as a % pediatric-to-adult ratio [Sp/Sa (%)]. Solubility ratios of fourteen poorly water-soluble drugs (2 amphoteric; 4 weak acids; 4 weak bases; 4 neutral compounds) were used in the analysis. Partial Least Squares Regression was based on Abraham solvation parameters and age-related changes in simulated gastrointestinal fluids, as well as their interactions, to predict the pediatric-to-adult solubility ratio. RESULTS: The use of Abraham solvation parameters was useful as a theory-informed set of molecular predictors of drug solubility changes between pediatric and adult simulated gastrointestinal fluids. Our findings suggest that the molecular solvation environment in the fasted gastric state was similar in the pediatric age-groups studied, which led to fewer differences in the pediatric-to-adult solubility ratio. In the intestinal fasted and fed state, there was a high relative contribution of the physiologically relevant surfactants to the alteration of drug solubility in the pediatric simulated conditions compared to the adult ones, which confirms the importance of an age-appropriate composition in biorelevant media. CONCLUSION: Statistical models based on Abraham solvation parameters were applied mostly to better understand drug solubility differences in adult and pediatric biorelevant media.

Investigating the Critical Variables of Azithromycin Oral Absorption Using In Vitro Tests and PBPK Modeling.

Azithromycin is an antibiotic listed in the essential list of medicines for adults and pediatrics. Conflicting evidence has been found regarding azithromycin classification according to the Biopharmaceutics classification system (BCS). The purpose of this study was to identify the critical variables that influence the oral absorption of azithromycin in adults and pediatrics. Azithromycin solubility and dissolution studies (oral suspension) were performed in buffers and biorelevant media simulating the fasted and fed gastrointestinal tract. A PBPK model was developed for azithromycin for healthy adult volunteers and pediatrics (Simcyp® v18.2) informed by in vitro solubility and dissolution studies to predict drug performance after administration of azithromycin as an oral suspension. The developed PBPK model predicted azithromycin plasma concentrations-time profiles after administration of an oral suspension to adults and pediatrics. Sensitivity analysis of solubility vs dose suggests that absorption is independent of solubility within the therapeutic dose range in both adults and pediatrics. The developed PBPK model for adults and pediatrics was consistent with the mechanism of permeation through the intestinal membrane (passive and active processes) being the rate-limiting step of azithromycin's absorption. The physiologically based approach proposed was shown to be useful to determine the factors controlling drug absorption in adults and pediatrics.

Investigating the Impact of Crohn's Disease on the Bioaccessibility of a Lipid-Based Formulation with an In Vitro Dynamic Gastrointestinal Model.

The aim of the study was to investigate the impact of Crohn's disease (CD) on the performance of a lipid-based formulation of ciprofloxacin in a complex gastrointestinal simulator (TIM-1, TNO) and to compare the luminal environment in terms of bile salt and lipid composition in CD and healthy conditions. CD conditions were simulated in the TIM-1 system with a reduced concentration of porcine pancreatin and porcine bile. The bioaccessibility of ciprofloxacin was similar in simulated CD and healthy conditions considering its extent as well as its time course in the jejunum and ileum filtrate. Differences were observed in terms of the luminal concentration of triglycerides, monoglycerides, and fatty acids in the different TIM-1 compartments, indicating a reduction and delay in the lipolysis of formulation excipients in CD. The quantitative analysis of bile salts revealed higher concentrations for healthy conditions (standard TIM-1 fasted-state protocol) in the duodenum and jejunum TIM-1 compartments compared to published data in human intestinal fluids of healthy subjects. The reduced concentrations of bile salts in simulated CD conditions correspond to the levels observed in human intestinal fluids of healthy subjects in the fasted state.A lipidomics approach with ultra performance liquid chromatography (UPLC)/mass spectrometry (MS) has proven to be a time-efficient method to semiquantitatively analyze differences in fatty acid and bile salt levels between healthy and CD conditions. The dynamic luminal environment in CD and healthy conditions after administration of a lipid-based formulation can be simulated using the TIM-1 system. For ciprofloxacin, an altered luminal lipid composition had no impact on its performance indicating a low risk of altered performance in CD patients.

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

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

Affinity of Lipophilic Drugs to Mixed Lipid Aggregates in Simulated Gastrointestinal Fluids.

Mixed lipid aggregates, comprising of bile salts and phospholipids, present in the small intestine assist in drug solubilization and subsequent drug dissolution and absorption through the intestinal epithelium. The increased variability in their levels, observed physiologically, may create challenges not only for in vivo bioavailability and bioequivalence studies, but also for in vitro bio-predictive studies as correlations between in vitro and in vivo data are not always successful. The current study investigated the impact of biorelevant dissolution media, with physiologically relevant sodium taurocholate and lecithin levels, on the apparent solubility and affinity of lipophilic compounds with a wide range of physicochemical properties (drug ionization, drug lipophilicity, molecular weight) to mixed lipid aggregates. Apparent solubility data in biorelevant dissolution media for the studied neutral drugs, weak bases and weak acids were compared against a phosphate buffer pH 6.5 in the absence of these lipidic components. Presence of mixed lipid aggregates enhanced the apparent solubility of the majority of compounds and the use of multivariate data analysis identified the significant parameters affecting drug affinity to mixed lipid aggregates based on the chemical class of the drug. For neutral drugs, increasing bile salt concentrations and/or drug lipophilicity resulted in greater enhancement in apparent solubility at 24-hr. For weak bases and weak acids, the effect of increasing bile salt levels on apparent solubility depended mostly on an interplay between drug lipophilicity and drug ionization.

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

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

Factors Affecting Successful Extrapolation of Ibuprofen Exposure from Adults to Pediatric Populations After Oral Administration of a Pediatric Aqueous Suspension.

The importance of physiologically based pharmacokinetic (PBPK) model refinement with data acquired in adults using a pediatric formulation under age-relevant dosing conditions in order to extrapolate drug exposure to infants was recently demonstrated for paracetamol. In the present investigation, the aim was to evaluate the importance of similar PBPK model refinement for a low-solubility weak acid, ibuprofen, to simulate exposure across pediatric populations, i.e., infants, young children, and schoolchildren. After developing and evaluating adult disposition and oral absorption models for the aqueous suspension of ibuprofen, ibuprofen performance was extrapolated to pediatrics simulating exposure as a function of different prandial and dosing conditions: fasted conditions, reference-meal fed conditions (solid-liquid meal), and infant-formula fed conditions (homogeneous liquid). Successful predictions were achieved when employing the refined model for fasted state conditions or for fed state conditions relevant to specific age groups, i.e., infant formula for infants and reference meal for children. The present study suggested that ibuprofen performance was primarily guided by gastric emptying and showed sensitivity towards formulation characteristics and pH changes in the small intestine. Better understanding of luminal conditions in pediatrics and age-dependent ibuprofen post-absorptive processes could improve modeling confidence for ibuprofen, as well as other drugs with similar characteristics.

Impact of Food and Drink Administration Vehicles on Paediatric Formulation Performance Part 2: Dissolution of Montelukast Sodium and Mesalazine Formulations.

Paediatric medicines are not always age-appropriate, causing problems with dosing, acceptability and adherence. The use of food and drinks as vehicles for medicine co-administration is common practice, yet the impact on drug bioavailability, safety and efficacy remains unaddressed. The aim of this study was to use in vitro dissolution testing, under infant simulating conditions, to evaluate the effect of co-administration with vehicles on the dissolution performance of two poorly soluble paediatric drugs. Dissolution studies of mesalazine and montelukast formulations were conducted with mini-paddle apparatus on a two-stage approach: simulated gastric fluid followed by addition of simulated intestinal fluid. The testing scenarios were designed to reflect daily administration practices: direct administration of formulation; formulation co-administered with food and drinks, both immediately after mixing and 4 h after mixing. Drug dissolution was significantly affected by medicine co-administration with vehicles, compared to the direct administration of formulation. Furthermore, differences were observed on drug dissolution when the formulations were mixed with different vehicles of the same subtype. The time between preparation and testing of the drug-vehicle mixture also impacted dissolution behaviour. Drug dissolution was shown to be significantly affected by the physicochemical properties and composition of the vehicles, drug solubility in each vehicle and drug/formulation characteristics. Ultimately, in this study, we show the potential of age-appropriate in vitro dissolution testing as a useful biopharmaceutical tool for estimating drug dissolution in conditions relevant to the paediatric population. The setup developed has potential to evaluate the impact of medicine co-administration with vehicles on paediatric formulation performance.

Successful Extrapolation of Paracetamol Exposure from Adults to Infants After Oral Administration of a Pediatric Aqueous Suspension Is Highly Dependent on the Study Dosing Conditions.

Extending licensed drug use to the pediatric population has become an essential part of the drug development process. Nonetheless, ethical concerns limit clinical testing in pediatric populations and data collected from oral bioavailability and food effect studies in adults are often extrapolated to the target pediatric (sub)populations. However, based on published information, food effects on drug absorption in infants may not be adequately evaluated by data collected in adults. In the present study, a physiologically based pharmacokinetic (PBPK) approach for modeling paracetamol suspension data collected in adults was proposed with the ultimate aim to investigate whether extrapolation to infants is substantially affected by the dosing conditions applied to adults. The development of the PBPK model for adults was performed using GastroPlus™ V9.7, and after scaling to infants considering physiological, anatomical, and drug clearance changes, extrapolation of the different dosing conditions was performed by applying dosing conditions dependent on changes on the paracetamol gastric emptying process. Successful simulations of previously observed plasma concentration levels in infants were achieved when extrapolating from fasted and infant formula-fed conditions data. Data collected following the reference meal appeared less useful for simulating paracetamol suspension performance in infants. The proposed methodology deserves further evaluation using high-quality clinical data both in adults and in infants.

The use of PBPK/PD to establish clinically relevant dissolution specifications for zolpidem immediate release tablets.

BACKGROUND: Zolpidem is a non-benzodiazepine hypnotic agent which has been shown to be effective in inducing and maintaining sleep in adults and is one of the most frequently prescribed hypnotics in the world. For drugs that are used to treat sleeping disorders, the time to reach the maximum concentration (Tmax) of the drug in plasma is important to achieving a fast onset of action and this must be maintained when switching from one product to another. OBJECTIVES: The main objective of the present work was to create a PBPK/PD model for zolpidem and establish a clinically relevant "safe space" for dissolution of zolpidem from the commercial immediate release (IR) formulation. A second objective was to analyze literature pharmacokinetic data to verify the negative food effect ascribed to zolpidem and consider its ramifications in terms of the "safe space" for dissolution. METHODS: Using dissolution, pharmacokinetic and pharmacodynamic data, an integrated PBPK/PD model for immediate release zolpidem tablets was constructed in Simcyp®. This model was used to identify the clinically relevant dissolution specifications necessary to ensure efficacy. RESULTS: According to the simulations, as long as 85% of the drug is released in 45 minutes or less, the impact on the PK and PD profiles of zolpidem would be minimal. According to the FDA, the drug has to dissolve from the test and reference products at a similar rate and to an extent of 85% in not more than 30 minutes to pass bioequivalence via the BCS-biowaiver test. Thus, the BCS-biowaiver specifications are somewhat more stringent than the "safe space" based on the PBPK/PD model. Published data from fasted and fed state pharmacokinetic studies suggest but do not prove a negative food effect of zolpidem. CONCLUSIONS: A PBPK/PD model indicates that current BCS-biowaiver criteria are more restrictive for immediate release zolpidem tablets than they need to be. In view of the close relationship between PK and PD, it remains advisable to avoid taking zolpidem tablets with or immediately after a meal, as indicated by the Stilnox® labeling.

Gastrointestinal diseases and their impact on drug solubility: Ulcerative Colitis.

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

Gastrointestinal diseases and their impact on drug solubility: Celiac disease.

The aim of this study was to develop an in vitro tool for predicting drug solubility and dissolution in intestinal fluids of patients with Celiac disease (CED). Biorelevant media for patients with CED were developed based on published information and a Design of Experiment (DoE) approach. The CED biorelevant media were characterised according to their surface tension, osmolality, dynamic viscosity and buffer capacity. By performing solubility studies of six drugs with different physicochemical properties in CED media, we aimed to identify drugs at high risk of altered luminal solubility in CED patients. Identified differences in CED patients compared to healthy subjects were related to a higher concentration of bile salts, lecithin and cholesterol and included as factors in the DoE resulting in 8 CED biorelevant media. Differences in media properties were observed for the surface tension between biorelevant media based on CED patients and healthy subjects. In terms of solubility, only a minimal effect of CED on the solubility of the hydrophilic neutral compound azathioprine was observed. For neutral moderately lipophilic compounds (budesonide, celecoxib), a higher surfactant concentration resulted in most cases in a higher drug solubility, while it was specific to each drug whether this was mainly driven by bile salts or lecithin. In comparison, drug solubilisation of ionisable compounds with moderate to high lipophilicity was less impacted by CED differences. The developed biorelevant CED media serve as in vitro tool to identify the main media factors impacting on drug solubility.