Intraluminal drug and formulation behavior and integration in in vitro permeability estimation: A case study with amprenavir

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.

Levocetirizine-Loaded Electrospun Fibers from Water-Soluble Polymers: Encapsulation and Drug Release

Electrospun fibers containing levocetirizine, a BCS III drug, were prepared from three water-soluble polymers, hydroxypropyl methylcellulose (HPMC), polyvinylpyrrolidone (PVP) and polyvinyl alcohol (PVA). Fiber-spinning technology was optimized for each polymer separately. The polymers contained 10 wt% of the active component. An amorphous drug was homogeneously distributed within the fibers. The solubility of the drug in the polymers used was limited, with a maximum of 2.0 wt%, but it was very large in most of the solvents used for fiber spinning and in the dissolution media. The thickness of the fibers was uniform and the presence of the drug basically did not influence it at all. The fiber diameters were in the same range, although somewhat thinner fibers could be prepared from PVA than from the other two polymers. The results showed that the drug was amorphous in the fibers. Most of the drug was located within the fibers, probably as a separate phase; the encapsulation efficiency proved to be 80-90%. The kinetics of the drug release were evaluated quantitatively by the Noyes-Whitney model. The released drug was approximately the same for all the polymers under all conditions (pH), and it changed somewhere between 80 and 100%. The release rate depended both on the type of polymer and pH and varied between 0.1 and 0.9 min^-1. Consequently, the selection of the carrier polymer allowed for the adjustment of the release rate according to the requirements, thus justifying the use of electrospun fibers as carrier materials for levocetirizine.

Development of In Vitro Dissolution Testing Methods to Simulate Fed Conditions for Immediate Release Solid Oral Dosage Forms

In vitro dissolution testing is widely used to mimic and predict in vivo performance of oral drug products in the gastrointestinal (GI) tract. This literature review assesses the current in vitro dissolution methodologies being employed to simulate and predict in vivo drug dissolution under fasted and fed conditions, with emphasis on immediate release (IR) solid oral dosage forms. Notable human GI physiological conditions under fasted and fed states have been reviewed and summarized. Literature results showed that dissolution media, mechanical forces, and transit times are key dissolution test parameters for simulating specific postprandial conditions. A number of biorelevant systems, including the fed stomach model (FSM), GastroDuo device, dynamic gastric model (DGM), simulated gastrointestinal tract models (TIM), and the human gastric simulator (HGS), have been developed to mimic the postprandial state of the stomach. While these models have assisted in expanding physiological relevance of in vitro dissolution tests, in general, these models lack the ability to fully replicate physiological conditions/processes. Furthermore, the translatability of in vitro data to an in vivo system remains challenging. Additionally, physiologically based pharmacokinetic (PBPK) modeling has been employed to evaluate the effect of food on drug bioavailability and bioequivalence. Here, we assess the current status of in vitro dissolution methodologies and absorption PBPK modeling approaches to identify knowledge gaps and facilitate further development of in vitro dissolution methods that factor in fasted and fed states. Prediction of in vivo drug performance under fasted and fed conditions via in vitro dissolution testing and modeling may potentially help efforts in harmonizing global regulatory recommendations regarding in vivo fasted and fed bioequivalence studies for solid oral IR products.

Improved Release of a Drug with Poor Water Solubility by Using Electrospun Water-Soluble Polymers as Carriers

In an attempt to improve the solubility of valsartan, a BCS II drug, fibers containing the drug were prepared from three water-soluble polymers, hydroxypropyl-methyl-cellulose (HPMC), polyvinyl-pyrrolidone (PVP), and polyvinyl-alcohol (PVA). Fiber spinning technology was optimized for each polymer separately. The polymers contained 20 wt% of the active component. The drug was homogenously distributed within the fibers in the amorphous form. The presence of the drug interfered with the spinning process only slightly, the diameters of the fibers were in the same range as without the drug for the HPMC and the PVA fibers, while it doubled in PVP. The incorporation of the drug into the fibers increased its solubility in all cases compared to that of the neat drug. The solubility of the drug itself depends very much on pH and this sensitivity remained the same in the HPMC and PVP fibers; the release of the drug is dominated by the dissolution behavior of valsartan itself. On the other hand, solubility and the rate of release were practically independent of pH in the PVA fibers. The different behavior is explained by the rate of the dissolution of the respective polymer, which is larger for HPMC and PVP, and smaller for PVA than the dissolution rate of the drug. The larger extent of release compared to neat valsartan can be explained by the lack of crystallinity of the drug, its better dispersion, and the larger surface area of the fibers. Considering all facts, the preparation of electrospun devices from valsartan and water-soluble polymers is beneficial, and the use of PVA is more advantageous than that of the other two polymers.

Integration of advanced methods and models to study drug absorption and related processes: An UNGAP perspective

This collection of contributions from the European Network on Understanding Gastrointestinal Absorption-related Processes (UNGAP) community assembly aims to provide information on some of the current and newer methods employed to study the behaviour of medicines. It is the product of interactions in the immediate pre-Covid period when UNGAP members were able to meet and set up workshops and to discuss progress across the disciplines. UNGAP activities are divided into work packages that cover special treatment populations, absorption processes in different regions of the gut, the development of advanced formulations and the integration of food and pharmaceutical scientists in the food-drug interface. This involves both new and established technical approaches in which we have attempted to define best practice and highlight areas where further research is needed. Over the last months we have been able to reflect on some of the key innovative approaches which we were tasked with mapping, including theoretical, in silico, in vitro, in vivo and ex vivo, preclinical and clinical approaches. This is the product of some of us in a snapshot of where UNGAP has travelled and what aspects of innovative technologies are important. It is not a comprehensive review of all methods used in research to study drug dissolution and absorption, but provides an ample panorama of current and advanced methods generally and potentially useful in this area. This collection starts from a consideration of advances in a priori approaches: an understanding of the molecular properties of the compound to predict biological characteristics relevant to absorption. The next four sections discuss a major activity in the UNGAP initiative, the pursuit of more representative conditions to study lumenal dissolution of drug formulations developed independently by academic teams. They are important because they illustrate examples of in vitro simulation systems that have begun to provide a useful understanding of formulation behaviour in the upper GI tract for industry. The Leuven team highlights the importance of the physiology of the digestive tract, as they describe the relevance of gastric and intestinal fluids on the behaviour of drugs along the tract. This provides the introduction to microdosing as an early tool to study drug disposition. Microdosing in oncology is starting to use gamma-emitting tracers, which provides a link through SPECT to the next section on nuclear medicine. The last two papers link the modelling approaches used by the pharmaceutical industry, in silico to Pop-PK linking to Darwich and Aarons, who provide discussion on pharmacometric modelling, completing the loop of molecule to man.

In vitro models to evaluate ingestible devices: Present status and current trends

Orally ingestible medical devices offer significant opportunity in the diagnosis and treatment of gastrointestinal conditions. Their development necessitates the use of models that simulate the gastrointestinal environment on both a macro and micro scale. An evolution in scientific technology has enabled a wide range of in vitro, ex vivo and in vivo models to be developed that replicate the gastrointestinal tract. This review describes the landscape of the existing range of in vitro tools that are available to characterize ingestible devices. Models are presented with details on their benefits and limitations with regards to the evaluation of ingestible devices and examples of their use in the evaluation of such devices is presented where available. The multitude of models available provides a suite of tools that can be used in the evaluation of ingestible devices that should be selected on the functionality of the device and the mechanism of its function.

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.

Exploring the Impact of Intestinal Fluid Components on the Solubility and Supersaturation of Danazol

Eleven simulated intestinal fluids (SIF) were designed using a Design of Experiment (DoE) approach. The DoE SIF covered a range of compositions of fasted state human intestinal fluid (FaHIF) with regard to pH, bile salt (BS), and phospholipid (PL). Using the model compound danazol, the apparent crystalline solubility (aCS) and apparent amorphous solubility (aAS), as well as the supersaturation propensity was determined in the DoE SIF media. The aCS of danazol was dependent on the composition of the SIF, with PL as the main factor, and a small effect from BS and an interaction between BS and PL. From the DoE solubility data a model was derived, which could predict aCS in commercially available SIF (FaSSIF-V1 and -V2) and in a range of FaHIF. The aAS of danazol was differently affected by the SIF composition than the aCS; PL was again the main factor influencing the aAS, but interactions between BS and pH, as well as pH and PL were also important. The supersaturation propensities of danazol in the DoE SIF media were affected by the same factors as the aCS. Hence, the supersaturation behaviour and aCS of danazol, were found to be closely related.

Effect of excipients on oral absorption process according to the different gastrointestinal segments

INTRODUCTION

Excipients are necessary to develop oral dosage forms of any Active Pharmaceutical Ingredient (API). Traditionally, excipients have been considered inactive and inert substances, but, over the years, numerous studies have contradicted this belief. This review focuses on the effect of excipients on the physiological variables affecting oral absorption along the different segments of the gastrointestinal tract. The effect of excipients on the segmental absorption variables are illustrated with examples to help understand the complexity of predicting their in vivo effects.

AREAS COVERED

The effects of excipients on disintegration, solubility and dissolution, transit time, and absorption are analyzed in the context of the different gastrointestinal segments and the physiological factors affecting release and membrane permeation. The experimental techniques used to study excipient effects and their human predictive ability are reviewed.

EXPERT OPINION

The observed effects of excipient in oral absorption process have been characterized in the past, mainly in vitro (i.e. in dissolution studies, in vitro cell culture methods or in situ animal studies). Unfortunately, a clear link with their effects in vivo, i.e. their impact on Cmax or AUC, which need a mechanistic approach is still missing. The information compiled in this review leads to the conclusion that the effect of excipients in API oral absorption and bioavailability is undeniable and shows the need of implementing standardized and reproducible preclinical tools coupled with mechanistic and predictive physiological-based models to improve the current empirical retrospective approach.

pH-dependent ileocolonic drug delivery, part II: preclinical evaluation of novel drugs and novel excipients

Novel drugs and novel excipients in pH-dependent ileocolonic drug delivery systems have to be tested in animals. Which animal species are suitable and what in vivo methods are used to verify ileocolonic drug delivery?

pH-dependent ileocolonic drug delivery, part I: in vitro and clinical evaluation of novel systems

After the pH dependency of novel pH-dependent ileocolonic drug delivery systems is confirmed in vitro, their performance should be evaluated in human volunteers.

Internalin AB-expressing recombinant Lactobacillus casei protects Caco-2 cells from Listeria monocytogenes-induced damages under simulated intestinal conditions

Background

Listeria monocytogenes is an intracellular foodborne pathogen that employs a number of strategies to survive challenging gastrointestinal conditions. It proliferates in the gut and subsequently causes listeriosis in high-risk individuals. Therefore, inhibition of its adherence to the intestinal receptors is crucial in controlling its infection. In this study, the effect of our previously developed recombinant Lactobacillus casei strain expressing invasion protein, Internalin AB of L. monocytogenes (Lbc^InlAB) on epithelial infection processes of the latter under simulated intestinal conditions was investigated.

Materials and methods

The confluent Caco-2 cell monolayer was pre-exposed to different L. casei strains at a multiplicity of exposure (MOE) of 10 for various periods before infection with L. monocytogenes at a multiplicity of infection (MOI) of 10 under simulated intestinal conditions. Subsequently, L. monocytogenes adhesion, invasion, and translocation, cytotoxicity and impact on tight junction integrity of the Caco-2 cells were analyzed.

Results

Under the simulated gastrointestinal condition, Lbc^InlAB showed a significant increase (p<0.0001) in adherence to, invasion and translocation through the Caco-2 cells when compared with the wild type strain. Although Lbc^InlAB strain exhibited enhanced inhibition of L. monocytogenes, it was not able to displace L. monocytogenes cells already attached to the monolayer. Additionally, pre-exposure to Lbc^InlAB reduced L. monocytogenes-mediated cytotoxicity and protected the tight junction barrier function.

Conclusion

The recombinant L. casei expressing InlAB shows potential for use as a prophylactic intervention strategy for targeted control of L. monocytogenes during the intestinal phase of infection.

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

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

Development and Characterization of a Self-Nanoemulsifying Drug Delivery System Comprised of Rice Bran Oil for Poorly Soluble Drugs

Poor aqueous solubility and low bioavailability are limiting factors in the oral delivery of lipophilic drugs. In a formulation approach to overcome these limitations, rice bran (RB) oil was evaluated as drug carrier in the development of self-nanoemulsifying drug delivery systems (SNEDDS). The performance of RB in formulations incorporating Kolliphor RH40 or Kolliphor EL as surfactants and Transcutol HP as cosolvent was compared to a common oil vehicle, corn oil (CO). Serial dilutions of the preconcentrates were performed in various media [distilled water and simulated intestinal fluids mimicking fasted state (FaSSIF) and fed state (FeSSIF)] and at different dilution ratios to simulate the in vivo droplets' behavior. The developed SNEDDS were assessed by means of phase separation, droplet size, polydispersity index, and ζ-potential. Complex ternary diagrams were constructed to identify compositions exhibiting monophasic behavior, droplet size < 100 nm, and polydispersity index (PDI) < 0.25. Multifactor analysis and response surface areas intended to determine the factors significantly affecting droplet size. The oil capacity to accommodate lipophilic drugs was assessed via fluorescence spectroscopy based on the solvatochromic behavior of Nile Red. Solubility studies were performed to prepare fenofibrate- and itraconazole-loaded SNEDDS and assess their droplet size, whereas dissolution experiments were conducted in simulated intestinal fluids. Caco-2 cell viability studies confirmed the safety of the SNEDDS formulations at 1:100 and 1:1000 dilutions after cell exposure in culture for 4 h. The obtained results showed similar performance between RB and CO supporting the potential of RB as oil vehicle for the effective oral delivery of lipophilic compounds.

Drug Delivery Innovations for Enhancing the Anticancer Potential of Vitamin E Isoforms and Their Derivatives

Vitamin E isoforms have been extensively studied for their anticancer properties. Novel drug delivery systems (DDS) that include liposomes, nanoparticles, and micelles are actively being developed to improve Vitamin E delivery. Furthermore, several drug delivery systems that incorporate Vitamin E isoforms have been synthesized in order to increase the bioavailability of chemotherapeutic agents or to provide a synergistic effect. D-alpha-tocopheryl polyethylene glycol succinate (Vitamin E TPGS or TPGS) is a synthetic derivative of natural alpha-tocopherol which is gaining increasing interest in the development of drug delivery systems and has also shown promising anticancer effect as a single agent. This review provides a summary of the properties and anticancer effects of the most potent Vitamin E isoforms and an overview of the various formulations developed to improve their efficacy, with an emphasis on the use of TPGS in drug delivery approaches.

Intestinal behavior of the ester prodrug tenofovir DF in humans

Tenofovir-disoproxil-fumarate (TDF) is a double ester prodrug which enables intestinal uptake of tenofovir (TFV) after oral administration in humans. In this study, prodrug stability was monitored in situ in the human intestine and in vitro using biorelevant media. In fasted state human intestinal fluids, the prodrug was completely degraded within 90 min, resulting in the formation of the mono-ester intermediate and TFV; in fed state intestinal fluids, the degradation rate of TDF was slightly reduced and no TFV was formed. Intestinal fluid samples aspirated after administration of TDF confirmed extensive intraluminal degradation of TDF in fasted state conditions; a relatively fast absorption of TDF partly compensated for the degradation. Although food intake reduced intestinal degradation, the systemic exposure was not proportionally increased. The lower degradation in fed state conditions may be attributed to competing esterase substrates present in food, lower chemical degradation in the slightly more acidic environment and micellar entrapment, delaying exposure to the "degrading" intestinal environment. The results of this study demonstrate premature intestinal degradation of TDF and suggest that TFV may benefit from a more stable prodrug approach; however, fast absorption may compensate for fast degradation, indicating that prodrug selection should not be limited to stability assays.

Structural features of colloidal species in the human fasted upper small intestine

Objectives

This paper aims to study the features of colloidal species in the lumen of the upper small intestine of two healthy adults at fasted state by means of electron microscopy.

Methods

Samples were aspirated from a location near the ligament of Treitz 30 min (volunteer no. 1, Aspirate30min sample) and 60 min (volunteer no. 2, Aspirate60min sample), after administration of 240 ml of an aqueous solution in the fasted state.

Key findings

In the Aspirate30min sample micelles coexist with multi-, oligo- and unilamellar vesicles. Tubular structures and long structures were frequently visualised. In the Aspirate60min sample micelles, few unilamellar vesicles, long structures and tubular structures were the dominating structural features. In both samples, multivesicular structures and faceted vesicles (previously visualised at fed state) were absent. Structural features of both samples bear similarities with previously studied samples from the lower intestine in the fasted state. Micelles and unilamellar vesicles observed in both samples closely resemble morphological characteristics of those found in fluids simulating the colloidal species in fasted upper intestinal environment.

Conclusions

Features of colloidal species in contents of fasted small intestine have similarities with fluids simulating the contents in fasted upper small intestine and with contents of lower intestine in the fasted state.

Evaluation of fasted and fed state simulated and human intestinal fluids as solvent system in the Ussing chambers model to explore food effects on intestinal permeability

The Ussing chambers model is almost exclusively used in the presence of plain aqueous phosphate buffers as solvent system. In an attempt to further elucidate the effect of luminal ingredients and postprandial conditions on intestinal permeability, pooled fasted and fed state human intestinal fluids (FaHIFpool, FeHIFpool) were used. In addition, simulated intestinal fluids of both nutritional states (FaSSIF, FeSSIF) were evaluated as possible surrogate media for HIF. The use of FaHIFpool generated a broad range of Papp values for a series of 16 model drugs, ranging from 0.03×10(-6)cm/s (carvedilol) to 33.8×10(-6)cm/s (naproxen). A linear correlation was observed between Papp values using FaSSIF and FaHIFpool as solvent system (R=0.990), justifying the use of FaSSIF as surrogate medium for FaHIF in the Ussing chambers. In exclusion of the outlier carvedilol, a strong sigmoidal relationship was found between Papp and fahuman of 15 model drugs, illustrated by correlation coefficients of 0.961 and 0.936 for FaHIFpool and FaSSIF, respectively. When addressing food effects on intestinal permeability, the use of FeHIFpool resulted in a significantly lower Papp value for nine out of sixteen compounds compared to fasting conditions. FeSSIF as solvent system significantly overestimated Papp values in FeHIFpool. To conclude, the optimized Ussing chambers model using biorelevant media as apical solvent system holds great potential to investigate food effects in a more integrative approach, taking into account drug solubilisation, supersaturation and formulation effects.

Composition and physicochemical properties of fasted-state human duodenal and jejunal fluid: a critical evaluation of the available data

Various methods of sampling and analyzing intestinal fluids have been applied over the years. In this report, data that have been published to date about the composition of fasted-state human intestinal fluid (HIF) and its physicochemical properties are summarized and the influence of the methods used to generate the data is discussed. Key physiological parameters summarized include pH, buffer capacity, osmolarity, and ionic strength in both the fasted duodenum and jejunum. Furthermore, the bile salts and phospholipids in the fasted small intestine are addressed in terms of both qualitative and quantitative composition with respect to the different types and degrees of hydroxylation of bile salts. Taurocholate, glycocholate, and glycochenodeoxycholate were identified as the main bile salts. Lysolecithin was identified as the predominant phospholipid species in fasted HIF because of the enzymatic degradation of lecithin. Together with other intestinal surfactants, such as cholesterol and free fatty acids, the influence of bile acids and phospholipids on the surface tension of fasted HIF was evaluated. A good working knowledge of all the above-mentioned parameters is important to optimize the composition of biorelevant media, with a view to improving the prediction of in vivo dissolution and release performance of drugs and dosage forms.

Biorelevant media for transport experiments in the Caco-2 model to evaluate drug absorption in the fasted and the fed state and their usefulness

In this work we developed and characterized transport media that simulate the composition of micellar phase of intestinal fluids in the fasted and, especially, in the fed state and are appropriate for evaluating intestinal drug permeability characteristics using the Caco-2 model (FaSSIF-TM(Caco) and FeSSIF-TM(Caco), respectively). Media composition was based on FaSSIF-V2 and FeSSIF-V2 and recently reported data on total lipid concentrations in the micellar phase of contents of the upper small intestine in the fasted and the fed state and was adapted for cell culture compatibility. Permeation data were evaluated by compartmental kinetic modeling. Permeability coefficients, P, of hydrophilic drugs were not affected by media composition. In contrast, P values of a series of lipophilic compounds measured with FaSSIF-TM(Caco) and FeSSIF-TM(Caco), and reflecting transport by diffusion were smaller than those obtained with a purely aqueous reference transport medium, aq-TM(Caco), following the rank order aq-TM(Caco)>FaSSIF-TM(Caco)>FeSSIF-TM(Caco). The decline of permeability values was stronger as lipophilicity of the compounds increased. Compared with values estimated using aq-TM(Caco), permeability was reduced, depending on the compound, by more than 20- to 100-fold when measured with FeSSIF-TM(Caco) whereas compound ranking in regard to the permeability characteristics was also affected. The impact of reduced P value on flux through the mucosa, hence on drug absorption, in combination with the drug amount loaded on colloidal particles needs to be taken into consideration in PBPK modeling especially when the food effect is evaluated.

Strategies to address low drug solubility in discovery and development

Drugs with low water solubility are predisposed to low and variable oral bioavailability and, therefore, to variability in clinical response. Despite significant efforts to "design in" acceptable developability properties (including aqueous solubility) during lead optimization, approximately 40% of currently marketed compounds and most current drug development candidates remain poorly water-soluble. The fact that so many drug candidates of this type are advanced into development and clinical assessment is testament to an increasingly sophisticated understanding of the approaches that can be taken to promote apparent solubility in the gastrointestinal tract and to support drug exposure after oral administration. Here we provide a detailed commentary on the major challenges to the progression of a poorly water-soluble lead or development candidate and review the approaches and strategies that can be taken to facilitate compound progression. In particular, we address the fundamental principles that underpin the use of strategies, including pH adjustment and salt-form selection, polymorphs, cocrystals, cosolvents, surfactants, cyclodextrins, particle size reduction, amorphous solid dispersions, and lipid-based formulations. In each case, the theoretical basis for utility is described along with a detailed review of recent advances in the field. The article provides an integrated and contemporary discussion of current approaches to solubility and dissolution enhancement but has been deliberately structured as a series of stand-alone sections to allow also directed access to a specific technology (e.g., solid dispersions, lipid-based formulations, or salt forms) where required.

Bile salts and their importance for drug absorption

Bile salts are present in the intestines of humans as well as the animals used during the development of pharmaceutical products. This review provides a short introduction into the physical chemical properties of bile salts, a description of the bile concentration and composition of bile in different animal species and an overview of the literature investigating the influence of bile salts on the in vivo performance of different compounds and drug formulations. Generally, there is a positive effect on bioavailability when bile is present in the gastro-intestinal tract, independent of the formulation systems, e.g. suspensions, solutions, cyclodextrin complexes or lipid based formulations, but a few exceptions have also been reported.

Designing a dynamic dissolution method: a review of instrumental options and corresponding physiology of stomach and small intestine

Development of new pharmaceutical compounds and dosage forms often requires in vitro dissolution testing with the closest similarity to the human gastrointestinal (GI) tract. To create such conditions, one needs a suitable dissolution apparatus and the appropriate data on the human GI physiology. This review discusses technological approaches applicable in biorelevant dissolutions as well as the physiology of stomach and small intestine in both fasted and fed state, that is, volumes of contents, transit times for water/food and various solid oral dosage forms, pH, osmolality, surface tension, buffer capacity, and concentrations of bile salts, phospholipids, enzymes, and Ca(2+) ions. The information is aimed to provide clear suggestions on how these conditions should be set in a dynamic biorelevant dissolution test.

The applications of Vitamin E TPGS in drug delivery

D-α-Tocopheryl polyethylene glycol 1000 succinate (simply TPGS or Vitamin E TPGS) is formed by the esterification of Vitamin E succinate with polyethylene glycol 1000. As novel nonionic surfactant, it exhibits amphipathic properties and can form stable micelles in aqueous vehicles at concentration as low as 0.02 wt%. It has been widely investigated for its emulsifying, dispersing, gelling, and solubilizing effects on poorly water-soluble drugs. It can also act as a P-glycoprotein (P-gp) inhibitor and has been served as an excipient for overcoming multidrug resistance (MDR) and for increasing the oral bioavailability of many anticancer drugs. Since TPGS has been approved by FDA as a safe pharmaceutic adjuvant, many TPGS-based drug delivery systems (DDS) have been developed. In this review, we discuss TPGS properties as a P-gp inhibitor, solubilizer/absorption and permeation enhancer in drug delivery and TPGS-related formulations such as nanocrystals, nanosuspensions, tablets/solid dispersions, adjuvant in vaccine systems, nutrition supplement, plasticizer of film, anticancer reagent and so on. This review will greatly impact and bring out new insights in the use of TPGS in DDS.

Lipid digestion as a trigger for supersaturation: evaluation of the impact of supersaturation stabilization on the in vitro and in vivo performance of self-emulsifying drug delivery systems

The generation of supersaturation in the gastrointestinal (GI) tract is an increasingly popular means of promoting oral absorption for poorly water-soluble drugs. The current study examined the impact of changes to the quantities of medium-chain (MC) lipid (Captex 300:Capmul MCM), surfactant (Cremophor EL) and cosolvent (EtOH), and the addition of polymeric precipitation inhibitors (PPI), on supersaturation during the dispersion and digestion of MC self-emulsifying drug delivery systems (SEDDS) containing danazol. The data suggest that digestion acts as a "trigger" for enhanced supersaturation and that solubilization/precipitation behavior is correlated with the degree of supersaturation on dispersion (S(M)DISP) or digestion (S(M)DIGEST). The ability of the formulation to maintain solubilization in vitro decreased as the S(M) of the formulation increased. PPI significantly increased supersaturation stabilization and precipitation was inhibited where S(M)DISP < 3.5 and S(M)DIGEST < 4. In the presence of polymer, some degree of supersaturation was maintained up to S(M)DIGEST ∼ 8. Differentiation in the ability of SEDDS to maintain drug solubilization stems from the ability to stabilize supersaturation and for MC SEDDS, utilization of lower drug loads, higher surfactant levels (balanced against increases in S(M)DISP), lower cosolvent and the addition of PPI enhanced formulation performance. In vivo studies confirmed the ability of PPI to promote drug exposure at moderate drug loads (40% of saturated solubility in the formulation). At higher drug loads (80% saturation) and in lipid-free SEDDS, this effect was lost, suggesting that the ability of PPIs to stabilize supersaturation in vitro may, under some circumstances, overestimate utility in vivo.

Preparation and evaluation of dermal delivery system of griseofulvin containing vitamin E-TPGS as penetration enhancer

Griseofulvin, an antifungal agent, is a BCS class II drug slowly, erratically, and incompletely absorbed from the gastrointestinal tract in humans. The clinical failure of the conventional oral therapy of griseofulvin is most likely attributed to its poor solubility and appreciable inter- and intra-subject variation in bioavailability from different commercial products. Moreover, the conventional oral therapy is associated with numerous adverse effects and interactions with other drugs. The purpose of the study was to formulate a topical application of griseofulvin which would deliver the drug locally in a therapeutically effective concentration. Griseofulvin was solubilized in ethanol, D-α-tocopheryl polyethylene glycol 1000 succinate (TPGS), and combinations of ethanol with varying amounts of TPGS; then, it was incorporated in the Carbopol (980 NF) base. The formulations were characterized and evaluated ex vivo using Laca mice skin, microbiologically against Microsporum gypseum and Microsporum canis and clinically in a small group of patients. The current study suggested that TPGS and ethanol synergistically enhanced the drug permeation and drug retention in the skin. The selected formulation F VII was found to be effective against M. gypseum and M. canis, non-sensitizing, histopathologically safe, stable at 4°C, 25°C, and 40°C with respect to percent drug content, permeation characteristics, pH, transparency, feel, viscosity, and clinically effective in a small group of subjects. The proposed topical formulation of griseofulvin may be an effective and convenient alternative to the currently available oral therapy for the treatment of superficial fungal infections.