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

Various gastrointestinal (GI) factors affect drug and formulation behavior after oral administration, including GI transfer, motility, pH and GI fluid volume and composition. An in-depth understanding of these physiological and anatomical variables is critical for a continued progress in oral drug development. In this review, different methodologies (invasive versus non-invasive) to explore the impact of physiological variables on formulation behavior in the human GI tract are presented, revealing their strengths and limitations. The techniques mentioned allow for an improved understanding of the role of following GI variables: gastric emptying (magnetic resonance imaging (MRI), scintigraphy, acetaminophen absorption technique, ultrasonography, breath test, intraluminal sampling and telemetry), motility (MRI, small intestinal/colonic manometry and telemetry), GI volume changes (MRI and ultrasonography), temperature (telemetry) and intraluminal pH (intraluminal sampling and telemetry)

Gastrointestinal and Systemic Monitoring of Posaconazole in Humans after Fasted and Fed State Administration of a Solid Dispersion

The purpose of this study was to explore the intraluminal behavior and systemic exposure of posaconazole in humans after oral intake of a novel delayed-release tablet (Noxafil(®)), containing posaconazole dispersed in a matrix of hydroxypropyl methylcellulose acetate succinate. Five healthy volunteers were asked to ingest the tablet in the fasted and fed state condition, after positioning one aspiration catheter in the stomach and one in the jejunum. Subsequently, gastric and jejunal fluids were aspirated and analyzed for posaconazole. In parallel, blood samples were collected. In gastric aspirates, dissolved concentrations were negligible regardless of the test condition, confirming the delayed-release properties of the tablet. In fasted state jejunal aspirates, sustained supersaturation was observed during an average period of time of 93 ± 78.2 min, with a mean maximum degree of supersaturation of 7.28 ± 8.81. In the fed state condition, supersaturation was negligible in the jejunum with a pronounced presence of solid posaconazole, suggesting the importance of more distal intestinal regions for posaconazole absorption.publisher: Elsevier articletitle: Gastrointestinal and Systemic Monitoring of Posaconazole in Humans After Fasted and Fed State Administration of a Solid Dispersion journaltitle: Journal of Pharmaceutical Sciences articlelink: http://dx.doi.org/10.1016/j.xphs.2016.03.027 content_type: article copyright: © 2016 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.status: publishe

Supersaturation and precipitation of posaconazole upon entry in the upper small intestine in humans

The purpose of this study was to explore gastrointestinal dissolution, supersaturation and precipitation of the weakly basic drug posaconazole in humans, and to assess the impact of formulation pH and type on these processes. In a cross-over study, two posaconazole suspensions (40 mg dispersed in 240 mL water at pH 1.6 and pH 7.1, respectively) were intragastrically administered; subsequently, gastric and duodenal fluids were aspirated. In parallel, blood samples were collected. Additionally, posaconazole was intragastrically administered as a solution (20 mg in 240 mL water, pH 1.6). When posaconazole was administered as an acidified suspension, supersaturated duodenal concentrations of posaconazole were observed for approximately 45 min. However, extensive intestinal precipitation was observed. Administration of the neutral suspension resulted in subsaturated concentrations with a mean duodenal AUC0-120 min and Cmax being approximately twofold lower than for the acidified suspension. The mean plasma AUC0-8 h of posaconazole was also twofold higher following administration of the acidified suspension. Similar to the acidified suspension, significant intestinal precipitation (up to 92%) was observed following intragastric administration of the posaconazole solution. This study demonstrated for the first time the gastrointestinal behavior of a weakly basic drug administered in different conditions, and its impact on systemic exposure.publisher: Elsevier articletitle: Supersaturation and Precipitation of Posaconazole Upon Entry in the Upper Small Intestine in Humans journaltitle: Journal of Pharmaceutical Sciences articlelink: http://dx.doi.org/10.1002/jps.24690 content_type: article copyright: © 2016 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.status: publishe

Gastrointestinal and systemic monitoring of posaconazole in humans after fasted and fed state administration of a solid dispersion

The purpose of this study was to explore the intraluminal behavior and systemic exposure of posaconazole in humans after oral intake of a novel delayed-release tablet (Noxafil®), containing posaconazole dispersed in a matrix of hydroxypropyl methylcellulose acetate succinate. Five healthy volunteers were asked to ingest the tablet in the fasted and fed state condition, after positioning one aspiration catheter in the stomach and one in the jejunum. Subsequently, gastric and jejunal fluids were aspirated and analyzed for posaconazole. In parallel, blood samples were collected. In gastric aspirates, dissolved concentrations were negligible regardless of the test condition, confirming the delayed-release properties of the tablet. In fasted state jejunal aspirates, sustained supersaturation was observed during an average period of time of 93 ± 78.2 min, with a mean maximum degree of supersaturation of 7.28 ± 8.81. In the fed state condition, supersaturation was negligible in the jejunum with a pronounced presence of solid posaconazole, suggesting the importance of more distal intestinal regions for posaconazole absorption

Bile salt micelles and phospholipid vesicles present in simulated and human intestinal fluids: Structural analysis by flow field-flow fractionation/multi-angle laser light scattering

Knowledge about colloidal assemblies present in human intestinal fluids (HIFs), such as bile salt micelles and phospholipid vesicles, is regarded of importance for a better understanding of the in vivo dissolution and absorption behavior of poorly soluble drugs (Biopharmaceutics Classification System class II/IV drugs) because of their drug-solubilizing ability. The characterization of these potential drug-solubilizing compartments is a prerequisite for further studies of the mechanistic interplays between drug molecules and colloidal structures within HIFs. The aim of the present study was to apply asymmetrical flow field-flow fractionation (AF4) in combination with multiangle laser light scattering in an attempt to reveal coexistence of colloidal particles in both artificial and aspirated HIFs and to determine their sizes. Asymmetrical flow field-flow fractionation/multiangle laser light scattering analysis of the colloidal phase of intestinal fluids allowed for a detailed insight into the whole spectrum of submicron- to micrometer-sized particles. With respect to the simulated intestinal fluids mimicking fasted and fed state (FaSSIF-V1 and FeSSIF-V1, respectively), FaSSIF contained one distinct size fraction of colloidal assemblies, whereas FeSSIF contained 2 fractions of colloidal species with significantly different sizes. These size fractions likely represent (1) mixed taurocholate-phospholipid-micelles, as indicated by a size range up to 70 nm (in diameter) and a strong UV absorption and (2) small phospholipid vesicles of 90-210 nm diameter. In contrast, within the colloidal phase of the fasted state aspirate of a human volunteer, 4 different size fractions were separated from each other in a consistent and reproducible manner. The 2 fractions containing large particles showed mean sizes of approximately 50 and 200 nm, respectively (intensity-weighted mean diameter, Dz), likely representing mixed cholate/phospholipid micelles and phospholipid vesicles, respectively. The sizes of the smaller 2 fractions being below the size range of multiangle laser light scattering analysis (<20 nm) and their strong UV absorption indicates that they represent either pure cholate micelles or small mixed micelles. Within the colloidal fraction of the fed-state human aspirate, similar colloidal assemblies were detected as in the fasted state human aspirates. The observed differences between SIF and HIF indicate that the simulated intestinal fluids (FaSSIF-V1 and FeSSIF-V1) represent rather simplified models of the real human intestinal environment in terms of coexisting colloidal particles. It is hypothesized that the different supramolecular assemblies detected differ in their lipid composition, which may affect their affinity toward drug compounds and thus the drug-solubilizing capabilities.publisher: Elsevier articletitle: Bile Salt Micelles and Phospholipid Vesicles Present in Simulated and Human Intestinal Fluids: Structural Analysis by Flow Field–Flow Fractionation/Multiangle Laser Light Scattering journaltitle: Journal of Pharmaceutical Sciences articlelink: http://dx.doi.org/10.1016/j.xphs.2016.03.005 content_type: article copyright: © 2016 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.status: publishe

Supersaturation in human gastric fluids

PURPOSE: The current study reports on supersaturation, precipitation and excipient mediated precipitation inhibition of five poorly soluble drugs (loviride, glibenclamide, itraconazole, danazol, and etravirine) in human and simulated gastric fluids. METHOD: Upon induction of supersaturation in human gastric fluids (HGFs), simulated gastric fluid (SGF), and fasted state simulated gastric fluid (FaSSGF) using a solvent shift method, supersaturation and precipitation were assessed as a function of time. In addition, the precipitation inhibitory capacity of three polymers (Eudragit® E PO, HPMC-E5, and PVP K25) was investigated. RESULTS: Supersaturation in human gastric fluids was observed for all model compounds, but proved to be relatively unstable (fast precipitation), except for itraconazole. Only modest excipient-mediated stabilizing effects on supersaturation were observed using HPMC-E5 and Eudragit® E PO whereas PVP K25 exerted no effect. In contrast to SGF, the observed precipitation behavior in FaSSGF was similar to the behavior in human gastric fluids. CONCLUSION: The present study demonstrates that supersaturation stability of drugs in human gastric fluids is in general inferior to supersaturation stability in intestinal fluids. As the potential for excipient mediated precipitation inhibition in gastric fluids was only limited, our data suggest that supersaturation should preferably be targeted to the intestine.status: publishe

In vitro evaluation of the impact of gastrointestinal transfer on luminal performance of commercially available products of posaconazole and itraconazole using BioGIT

Biorelevant Gastrointestinal Transfer system (BioGIT) has been shown to be useful in reproducing concentrations of drugs in the fasted upper small intestine after their administration in the stomach. In the present investigation, we evaluated the impact of gastrointestinal transfer on luminal performance of commercially available products of two highly lipophilic weak bases, posaconazole (Noxafil® suspension) and itraconazole (Sporanox® hard gelatin capsules and Sporanox® oral solution) by comparing % solid fraction, concentrations and supersaturation in the duodenal compartment of BioGIT with recently reported data in the upper small intestine of healthy adults. BioGIT was useful for estimating the % solid fraction in the upper small intestine, in cases where dissolution during gastric residence was incomplete, i.e. after administration of Noxafil® and Sporanox® capsules, and the precipitated fraction of itraconazole in the upper small intestine after administration of Sporanox® solution; median values in vitro were similar to the luminal values. Based on the values for the area under the concentration vs. time data estimated up to 45min post initiation of the experiment, concentrations in the duodenal compartment of BioGIT were similar to previously measured concentrations in the upper small intestine of healthy adults or they overestimated them by up to 2.5 times. In most cases, supersaturation of contents in the upper small intestine was overestimated, partly due to underestimation of luminal solubility.publisher: Elsevier articletitle: In vitro evaluation of the impact of gastrointestinal transfer on luminal performance of commercially available products of posaconazole and itraconazole using BioGIT journaltitle: International Journal of Pharmaceutics articlelink: http://dx.doi.org/10.1016/j.ijpharm.2016.10.018 content_type: article copyright: © 2016 Elsevier B.V. All rights reserved.status: publishe

Gastrointestinal Transfer: In Vivo Evaluation and Implementation in In Vitro and In Silico Predictive Tools

INTRODUCTION: The purpose of this study was to explore the transfer of drug solutions from stomach to small intestine and its impact on intraluminal drug concentrations in humans. The collected intraluminal data were used as reference to evaluate simulations of gastrointestinal transfer currently implemented in different in vitro and in silico absorption models. METHODS: Gastric and duodenal concentrations of the highly soluble and non-absorbable compound paromomycin were determined following oral administration to 5 healthy volunteers under the following conditions: fasted state, fed state and fed state in the presence of a transit-stimulating (domperidone) or transit-inhibiting (loperamide) agent. Based on the obtained intraluminal concentration-time profiles, gastrointestinal transfer (expressed as the half-life of gastric emptying) was analyzed using physiologically-based parameter estimation in Simcyp®. Subsequently, the observed transfer profiles were used to judge the implementation of gastrointestinal transfer in 2 in vitro simulation tools (the TNO Intestinal Model TIM-1 and a three-compartmental in vitro model) and the Simcyp® population-based PBPK modeling platform. RESULTS: The observed duodenal concentration-time profile of paromomycin under fasting conditions, with a high average Cmax obtained after 15 min, clearly indicated a fast transfer of drug solutions from stomach to duodenum (estimated gastric half-life between 4 and 13 min). The three-compartmental in vitro model adequately reflected the in vivo fasted state gastrointestinal transfer of paromomycin. For both TIM-1 and Simcyp®, modifications in gastric emptying and dilutions were required to improve the simulation of the transfer of drug solutions. As expected, transfer from stomach to duodenum was delayed in the fed state, resulting in lower duodenal paromomycin concentrations and an estimated gastric half-life between 21 and 40 min. Administration of domperidone or loperamide as transit-stimulating and transit-inhibiting agent, respectively, did not affect the fed state gastric half-life of emptying. CONCLUSION: For the first time, the impact of gastrointestinal transfer of solutions on intraluminal drug concentrations was directly assessed in humans. In vitro and in silico simulation tools have been validated and optimized using the in vivo data as reference.publisher: Elsevier articletitle: Gastrointestinal transfer: In vivo evaluation and implementation in in vitro and in silico predictive tools journaltitle: European Journal of Pharmaceutical Sciences articlelink: http://dx.doi.org/10.1016/j.ejps.2014.07.008 content_type: article copyright: Copyright © 2014 Elsevier B.V. All rights reserved.status: publishe

Physiologically based pharmacokinetic (PBPK) modeling approach for the prediction of small intestinal precipitation of poorly soluble drugs - a simulation study of posaconazole using Simcyp ADAM model

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In Silico Modeling Approach for the Evaluation of Gastrointestinal Dissolution, Supersaturation and Precipitation of Posaconazole

The aim of this study was to evaluate gastrointestinal (GI) dissolution, supersaturation, and precipitation of posaconazole, formulated as an acidified (pH 1.6) and neutral (pH 7.1) suspension. A physiologically based pharmacokinetic (PBPK) modeling and simulation tool was applied to simulate GI and systemic concentration-time profiles of posaconazole, which were directly compared with intraluminal and systemic data measured in humans. The Advanced Dissolution Absorption and Metabolism (ADAM) model of the Simcyp Simulator correctly simulated incomplete gastric dissolution and saturated duodenal concentrations of posaconazole in the duodenal fluids following administration of the neutral suspension. In contrast, gastric dissolution was approximately 2-fold higher after administration of the acidified suspension, which resulted in supersaturated concentrations of posaconazole upon transfer to the upper small intestine. The precipitation kinetics of posaconazole were described by two precipitation rate constants, extracted by semimechanistic modeling of a two-stage medium change in vitro dissolution test. The 2-fold difference in exposure in the duodenal compartment for the two formulations corresponded with a 2-fold difference in systemic exposure. This study demonstrated for the first time predictive in silico simulations of GI dissolution, supersaturation, and precipitation for a weakly basic compound in part informed by modeling of in vitro dissolution experiments and validated via clinical measurements in both GI fluids and plasma. Sensitivity analysis with the PBPK model indicated that the critical supersaturation ratio (CSR) and second precipitation rate constant (sPRC) are important parameters of the model. Due to the limitations of the two-stage medium change experiment the CSR was extracted directly from the clinical data. However, in vitro experiments with the BioGIT transfer system performed after completion of the in silico modeling provided an almost identical CSR to the clinical study value; this had no significant impact on the PBPK model predictions.status: publishe