The use of biopharmaceutic classification of drugs in drug discovery and development: current status and future extension

Ethanol-based solubility-enabling oral drug formulation development: Accounting for the solubility-permeability interplay

The aim of the current work was to investigate the key factors that govern the success/failure of an ethanol-based solubility-enabling oral drug formulation, including the effects of the ethanol on the solubility of the drug, the permeability across the intestinal membrane, the drug's dissolution in the aqueous milieu of the gastrointestinal tract (GIT), and the resulting solubility-permeability interplay. The concentration-dependent effects of ethanol-based vehicles on the solubility, the in-vitro Caco-2 permeability, the in-vivo rat permeability, and the biorelevant dissolution of the BCS class II antiepileptic drug carbamazepine were studied, and a predictive model describing the solubility-permeability relationship was developed. Significant concentration-dependent solubility increase of CBZ was obtained with increasing ethanol levels, that was accompanied by permeability decrease, both in Caco-2 and in rat perfusion studies, demonstrating a tradeoff between the increased solubility afforded by the ethanol and a concomitant permeability decrease. When ethanol absorption was accounted for, an excellent agreement was achieved between the predicted permeability and the experimental data. Biorelevant dissolution studies revealed that minimal ethanol levels of 30 % and 50 % were needed to fully dissolve 1 and 5 mg CBZ dose respectively, with no drug precipitation.In conclusion, key factors to be accounted for when developing ethanol-based formulation include the drug's solubility, permeability, the solubility-permeability interplay, and the drug dose intended to be delivered. Only the minimal amount of ethanol sufficient to solubilize the drug dose throughout the GIT should be used, and not more than that, to avoid unnecessarily permeability loss, and to maximize overall drug absorption.

Solubility-enabling formulations for oral delivery of lipophilic drugs: considering the solubility-permeability interplay for accelerated formulation development

INTRODUCTION

Tackling low water solubility of drug candidates is a major challenge in today's pharmaceutics/biopharmaceutics, especially by means of modern solubility-enabling formulations. However, drug absorption from these formulations oftentimes remains unchanged or even decreases, despite substantial solubility enhancement.

AREAS COVERED

In this article, we overview the simultaneous effects of the formulation on the solubility and the apparent permeability of the drug, and analyze the contribution of this solubility-permeability interplay to the success/failure of the formulation to increase the overall absorption and bioavailability. Three different patterns of interplay were identified: (1) solubility-permeability tradeoff in which every solubility gain comes with a price of concomitant permeability loss; (2) an advantageous interplay pattern in which the permeability remains unchanged alongside the solubility gain; and (3) an optimal interplay pattern in which the formulation increases both the solubility and the permeability. Passive vs. active intestinal permeability considerations in the context of the solubility-permeability interplay are also thoroughly discussed.

EXPERT OPINION

The solubility-permeability interplay pattern of a given formulation has a critical effect on its overall success/failure, and hence, taking into account both parameters in solubility-enabling formulation development is prudent and highly recommended.

Managing the clinical effects of drug-induced intestinal dysbiosis with a focus to antibiotics: Challenges and opportunities

The term "intestinal dysbiosis" is used for indicating change(s) of the intestinal microbiota which have been associated with the development of diseases and the deterioration of disease treatments in humans. In this review, documented clinical effects of drug-induced intestinal dysbiosis are briefly presented, and methodologies which could be considered for the management of drug-induced intestinal dysbiosis based on clinical data are critically reviewed. Until relevant methodologies are optimized and/or their effectiveness to the general population is confirmed, and, since drug-induced intestinal dysbiosis refers predominantly to antibiotic-specific intestinal dysbiosis, a pharmacokinetically-based approach for mitigating the impact of antimicrobial therapy on intestinal dysbiosis is proposed.

Citric acid esterified Glutinous Assam bora rice starch enhances disintegration and dissolution efficiency of model drug

The current work was designed to study the starch's physicochemical attributes, tablet disintegration and dissolution efficiency and its derivatives obtained from the glutinous Assam bora rice (G-ABR) variety of Assam, Northeast India. Starch was isolated by a simple protein denaturation method, and a starch derivative was prepared through citric acid modification. G-ABRS and citrated G-ABRS were characterized through FTIR, DSC, XRD and SEM. The rate of consolidation, consolidation index, angle of internal friction, packing rearrangement and cohesive properties were determined to investigate their applications as functional excipients in pharmaceutical industries. G-ABRS and citrated G-ABRS exhibited better packing rearrangement and cohesive properties than standard corn starch. Furthermore, immediate release of API from the tablet compact was observed when the starch concentration increased from 1 to 5 %, indicating facilitation of the tablet compact disintegration. Therefore, G-ABRS and citrated G-ABRS are potentially functional and sustainable materials for pharmaceutical industries.

Potential roles of gut microbes in biotransformation of natural products: An overview

Natural products have been extensively applied in clinical practice, characterized by multi-component and multi-target, many pharmacodynamic substances, complex action mechanisms, and various physiological activities. For the oral administration of natural products, the gut microbiota and clinical efficacy are closely related, but this relationship remains unclear. Gut microbes play an important role in the transformation and utilization of natural products caused by the diversity of enzyme systems. Effective components such as flavonoids, alkaloids, lignans, and phenols cannot be metabolized directly through human digestive enzymes but can be transformed by enzymes produced by gut microorganisms and then utilized. Therefore, the focus is paid to the metabolism of natural products through the gut microbiota. In the present study, we systematically reviewed the studies about gut microbiota and their effect on the biotransformation of various components of natural products and highlighted the involved common bacteria, reaction types, pharmacological actions, and research methods. This study aims to provide theoretical support for the clinical application in the prevention and treatment of diseases and provide new ideas for studying natural products based on gut biotransformation.

PAMAM Dendrimers: A Review of Methodologies Employed in Biopharmaceutical Classification

The oral route is the preferred way of drug administration for most drugs, whose treatment success is directly related to the compound intestinal absorption. This absorption process, in its turn, is influenced by several factors impacting the drug bioavailability, which is extremely dependent on the maximum solubility and permeability. However, optimizing these last two factors, without chemical structural modification, is challenging. Although poly(amidoamine) dendrimers (PAMAM) are an innovative and promising strategy as drug delivery compounds, there are few studies that determine the permeability and solubility of PAMAM-drugs derivatives. Considering this scenario, this paper aimed to carry out a literature review of the last five years concerning biopharmaceutical characterizations of dendrimer delivery systems. In vitro methodologies, such as the Parallel artificial membrane permeability assay (PAMPA) (non-cellular based model) and Caco-2 cells (cellular based model), used for the permeability evaluation in the early stages of drug discovery proved to be the most promising methodologies. As a result, we discussed, for instance, that through the usage of PAMPA it was possible to evaluate the higher capacity for transdermal delivery of DNA of TAT-conjugated PAMAM, when in comparison with unmodified PAMAM dendrimer with a P<0.05. We also presented the importance of choosing the best methods of biopharmaceutical characterization, which will be essential to guarantee the efficacy and safety of the drug candidate.

The Role of Paracellular Transport in the Intestinal Absorption and Biopharmaceutical Characterization of Minoxidil

The purpose of this study was to evaluate mechanisms behind the intestinal permeability of minoxidil, with special emphasis on paracellular transport, and elucidate the suitability of minoxidil to be a reference drug for Biopharmaceutics Classification System (BCS). The permeability of minoxidil (vs. metoprolol) was evaluated in-silico, in-vitro using both the PAMPA assay and across Caco-2 cell monolayers, as well as in-vivo in rats throughout the entire intestine. The permeability was studied in conditions that represent the different segments of the small intestine: upper jejunum (pH 6.5), mid small intestine (pH 7.0), distal ileum (pH 7.5), and colon (pH 6.5). Since we aimed to investigate the paracellular transport of minoxidil, we have also examined its permeability in the presence of quercetin (250 µM), which closes the tight junctions, and sodium decanoate (10 mM), which opens the tight junctions. While metoprolol demonstrated segmental-dependent rat and PAMPA permeability, with higher permeability in higher pH regions, the permeability of minoxidil was pH-independent. Minoxidil PAMPA permeability was significantly lower than its rat permeability, indicating a potential significant role of the paracellular route. In rat intestinal perfusion studies, and across Caco-2 monolayers, tight junction modifiers significantly affected minoxidil permeability; while the presence of quercetin caused decreased permeability, the presence of sodium decanoate caused an increase in minoxidil permeability. In accordance with these in-vitro and in-vivo results, in-silico simulations indicated that approximatelly 15% of minoxidil dose is absorbed paracellularly, mainly in the proximal parts of the intestine. The results of this study indicate that paracellular transport plays a significant role in the intestinal permeability of minoxidil following oral administration. Since this permeation route may lead to higher variability in comparison to transcellular, these findings diminish the suitability of minoxidil to serve as the low/high BSC permeability class benchmark.

Pharmaceutical nanococrystal synthesis: a novel grinding approach

Nanococrystals – a new green in situ surfactant-assisted mechanochemical synthesis.

Assessing the Intestinal Permeability of Small Molecule Drugs via Diffusion Motion on a Multidimensional Free Energy Surface

A protocol that accurately assesses the intestinal permeability of small molecule compounds plays an essential role in decreasing the cost and time in inventing a new drug. This manuscript presents a novel computational method to study the passive permeation of small molecule drugs based on the inhomogeneous solubility-diffusion model. The multidimensional free energy surface of the drug transiting through a lipid bilayer is computed with transition-tempered metadynamics that accurately captures the mechanisms of passive permeation. The permeability is computed by following the diffusion motion of the drug molecules along the minimal free energy path found on the multidimensional free energy surface. This computational method is assessed by studying the permeability of five small molecule drugs (ketoprofen, naproxen, metoprolol, propranolol, and salicylic acid). The results demonstrate a remarkable agreement between the computed permeabilities and those measured with the intestinal assay. The in silico method reported in this manuscript also reproduces the permeability measured from the intestinal assay (in vivo) better than the cell-based assays (e.g., PAMPA and Caco-2) do. In addition, the multidimensional free energy surface reveals the interplay between the structure of the small molecule and its permeability, shedding light on strategies of drug optimization.

Lamotrigine therapy in patients after bariatric surgery: Potentially hampered solubility and dissolution

Bariatric surgery is an effective treatment of obesity and related comorbidities. With surgery, the stomach undergoes major anatomical/physiological changes that may affect the oral exposure of drugs, especially marginally soluble weak bases, such as lamotrigine. The aim of this work was to study the solubility/dissolution of lamotrigine in conditions simulating the stomach before vs. after bariatric surgery. Lamotrigine solubility was studied in-vitro, as well as ex-vivo in gastric content aspirated from patients before vs. after bariatric surgery. We then compared the dissolution kinetics of various marketed lamotrigine products in pre- vs. post-operative stomach conditions, different in volume, pH, agitation strength and speed. Decreased lamotrigine solubility with increasing pH (from 1.37 ± 0.09 (pH = 1) to 0.22 ± 0.03 mg/mL (pH = 7)) was obtained. Twelve-fold higher lamotrigine solubility was revealed in gastric content aspirated before vs. after surgery (8.5 ± 0.7 and 0.7 ± 0.01 mg/mL, respectively). Dissolution studies showed that only the lowest dose (25 mg) fully dissolved in the post-surgery stomach conditions, while at higher doses, lamotrigine tablet dissolution was impaired. Neither fast-dissolving tablet, nor tablet crushing, helped resolving this problem. Based on these results, and given that dissolution of the drug dose governs the subsequent absorption, close monitoring of this essential drug is advised after bariatric surgery.

Nanomedicine-based technologies and novel biomarkers for the diagnosis and treatment of Alzheimer's disease: from current to future challenges

Increasing life expectancy has led to an aging population, which has consequently increased the prevalence of dementia. Alzheimer's disease (AD), the most common form of dementia worldwide, is estimated to make up 50-80% of all cases. AD cases are expected to reach 131 million by 2050, and this increasing prevalence will critically burden economies and health systems in the next decades. There is currently no treatment that can stop or reverse disease progression. In addition, the late diagnosis of AD constitutes a major obstacle to effective disease management. Therefore, improved diagnostic tools and new treatments for AD are urgently needed. In this review, we investigate and describe both well-established and recently discovered AD biomarkers that could potentially be used to detect AD at early stages and allow the monitoring of disease progression. Proteins such as NfL, MMPs, p-tau217, YKL-40, SNAP-25, VCAM-1, and Ng / BACE are some of the most promising biomarkers because of their successful use as diagnostic tools. In addition, we explore the most recent molecular strategies for an AD therapeutic approach and nanomedicine-based technologies, used to both target drugs to the brain and serve as devices for tracking disease progression diagnostic biomarkers. State-of-the-art nanoparticles, such as polymeric, lipid, and metal-based, are being widely investigated for their potential to improve the effectiveness of both conventional drugs and novel compounds for treating AD. The most recent studies on these nanodevices are deeply explained and discussed in this review.

Physiologically Based Biopharmaceutics Modeling of Regional and Colon Absorption in Dogs

Colon absorption is a key determinant for the successful development of modified-release (MR) formulations, and the risk that colon absorption may limit the in vivo performance of an MR product can be assessed early by various in vitro tests or by preclinical in vivo regional absorption studies in dogs. Mechanistic physiologically based biopharmaceutics modeling (PBBM) is becoming increasingly accepted to predict in vivo performance and guide formulation development; however, no evaluation of the ability to predict colon absorption has been performed. The purpose of this study was to investigate if regional and colon absorption of drugs in dogs could be predicted with sufficient accuracy using PBBM to enable the replacement of in vivo dog studies in the early assessment of colon absorption limitation risks. This was done by predicting the regional and colon absorption and plasma exposure of 14 drugs after administration to the dog colon according to an a priori approach using the in silico absorption models GI-Sim and GastroPlus. Predictive performance was primarily assessed by comparing observed and predicted plasma concentration-time profiles, AUC_0-t, and the relative bioavailability in the colon (F_rel,colon) as compared to an oral/duodenal reference. Trends in dependency of prediction performance on predicted fraction absorbed, permeability, and solubility/dissolution rate were also investigated. For GI-Sim, the absolute average fold error (AAFE) values for AUC_0-t and F_rel,colon were within a 2-fold prediction error for both solutions (1.88 and 1.51, respectively) and suspensions (1.58 and 1.99, respectively). For GastroPlus, the AAFE values for AUC_0-t and F_rel,colon were outside the set 2-fold prediction error limit for accurate predictions for both solutions (3.63 and 2.98, respectively) and suspensions (2.94 and 2.09, respectively). No trends for over- or underprediction were observed for GI-Sim, whereas GastroPlus showed a slight trend for underprediction of both AUC_0-t and F_rel,colon for compounds with low permeability. In addition, regional differences in the plasma profiles were qualitatively predicted in the majority of cases for both software. Despite the differences in prediction performance, both models can be considered to predict regional differences in absorption as well as AUC_0-t and F_rel,colon with acceptable accuracy in an early development setting. The results of this study indicate that it is acceptable to replace in vivo regional absorption studies in dogs with the evaluated models as a method for the early assessment of the risk for colon absorption limitation of MR drug product candidates.

ACTUALITIES IN ENDOCRINE PHARMACOLOGY: ADVANCES IN THE DEVELOPMENT OF ORAL FORMULATIONS FOR CALCITONIN AND SEMAGLUTIDE

As the medical utility of injectable therapeutic peptides is expanding, so is the challenge of developing technologies that allow the administration of such molecules via alternative routes, considering that chronic patients requiring treatment with parenteral formulations are less adherent and compliant to the therapeutic regimens. Hence, substantial efforts have been made to develop technologies that allow the oral formulation of peptides. Due to their importance in the field of pharmaceutical technology, we describe the latest advancements made in the development of oral salmon calcitonin and oral semaglutide, in co-formulation with absorption enhancers such as 8-[(5-chloro-2-hydroxybenzoyl) amino] octanoic acid (or 5-CNAC) and N-[8-(2-hydroxybenzoyl) amino] caprylate (or SNAC). Oral semaglutide is considered to be a landmark for oral peptide delivery technology, as it is one of the very few successful examples of peptides that can be administered orally. Unlike semaglutide, oral calcitonin is still not approved by the regulatory authorities because it failed to demonstrate the anticipated effects in phase III clinical trials conducted so far. However, the efforts for obtaining an oral form of calcitonin have significantly contributed to the development of technologies that facilitate the absorption of peptide-structure macromolecules.

Nanotechnology and its challenges in the food sector: a review

Antibacterial activity of nanoparticles has received significant attention worldwide because of their great physical and chemical stability, excellent magnetic properties, and large lattice constant values. These properties are predominate in the food science for enhancing the overall quality, shelf life, taste, flavor, process-ability, etc., of the food. Nanoparticles exhibit attractive antibacterial activity due to their increased specific surface area leading to enhanced surface reactivity. When nanoparticles are suspended in the biological culture, they encounter various biological interfaces, resulting from the presence of cellular moieties like DNA, proteins, lipids, polysaccharides, etc., which helps antibacterial properties in many ways. This paper reviews different methods used for the synthesis of nanoparticles but is specially focusing on the green synthesis methods owing to its non-toxic nature towards the environment. This review highlights their antibacterial application mainly in the food sector in the form of food-nanosensors, food-packaging, and food-additives. The possible mechanism of nanoparticles for their antibacterial behavior underlying the interaction of nano-particles with bacteria, (i) excessive ROS generation including hydrogen peroxide (H₂O₂), OH^- (hydroxyl radicals), and O^- ₂ ² (peroxide); and (ii) precipitation of nano-particles on the bacterial exterior; which, disrupts the cellular activities, resulting in membranes disturbance. All these phenomena results in the inhibition of bacterial growth. Along with this, their current application and future perspectives in the food sector are also discussed. Nanoparticles help in destroying not only pathogens but also deadly fungi and viruses. Most importantly it is required to focus more on the crop processing and its containment to stop the post-harvesting loss. So, nanoparticles can act as a smart weapon towards the sustainable move.

Biopharmaceutical considerations in paediatrics with a view to the evaluation of orally administered drug products - a PEARRL review

OBJECTIVES

In this review, the current biopharmaceutical approaches for evaluation of oral formulation performance in paediatrics are discussed.

KEY FINDINGS

The paediatric gastrointestinal (GI) tract undergoes numerous morphological and physiological changes throughout its development and growth. Some physiological parameters are yet to be investigated, limiting the use of the existing in vitro biopharmaceutical tools to predict the in vivo performance of paediatric formulations. Meals and frequencies of their administration evolve during childhood and affect oral drug absorption. Furthermore, the establishment of a paediatric Biopharmaceutics Classification System (pBCS), based on the adult Biopharmaceutics Classification System (BCS), requires criteria adjustments. The usefulness of computational simulation and modeling for extrapolation of adult data to paediatrics has been confirmed as a tool for predicting drug formulation performance. Despite the great number of successful physiologically based pharmacokinetic models to simulate drug disposition, the simulation of drug absorption from the GI tract is a complicating issue in paediatric populations.

SUMMARY

The biopharmaceutics tools for investigation of oral drug absorption in paediatrics need further development, refinement and validation. A combination of in vitro and in silico methods could compensate for the uncertainties accompanying each method on its own.

In Vitro Bioavailability Study of an Antiviral Compound Enisamium Iodide

An investigation into the biopharmaceutics classification and a study of the in vitro bioavailability (permeability and solubility) of the antiviral compound enisamium iodide (4-(benzylcarbamoyl)-1-methylpyridinium iodide) were carried out. The solubility of enisamium iodide was determined in four different buffers. Apparent intestinal permeability (P_app) of enisamium iodide was assessed using human colon carcinoma (Caco-2) cells at three concentrations. The solubility of enisamium iodide in four buffer solutions from pH 1.2 to 7.5 is about 60 mg/mL at 25 °C, and ranges from 130 to 150 mg/mL at 37 °C, depending on the pH. Based on these results, enisamium iodide can be classified as highly soluble. Enisamium iodide demonstrated low permeability in Caco-2 experiments in all tested concentrations of 10-100 μM with permeability coefficients between 0.2 × 10^-6 cm s^-1 and 0.3 × 10^-6 cm s^-1. These results indicate that enisamium iodide belongs to class III of the Biopharmaceutics Classification System (BCS) due to its high solubility and low permeability. The bioavailability of enisamium iodide needs to be confirmed in animal and human studies.

Active intestinal drug absorption and the solubility-permeability interplay

The solubility-permeability interplay deals with the question: what is the concomitant effect on the drug's apparent permeability when increasing the apparent solubility with a solubility-enabling formulation? The solubility and the permeability are closely related, exhibit certain interplay between them, and ongoing research throughout the past decade shows that treating the one irrespectively of the other may be insufficient. The aim of this article is to provide an overview of the current knowledge on the solubility-permeability interplay when using solubility-enabling formulations for oral lipophilic drugs, highlighting active permeability aspects. A solubility-enabling formulation may affect the permeability in opposite directions; the passive permeability may decrease as a result of the apparent solubility increase, according to the solubility-permeability tradeoff, but at the same time, certain components of the formulation may inhibit/saturate efflux transporters (when relevant), resulting in significant apparent permeability increase. In these cases, excipients with both solubilizing and e.g. P-gp inhibitory properties may lead to concomitant increase of both the solubility and the permeability. Intelligent development of such formulation will account for the simultaneous effects of the excipients' nature/concentrations on the two arms composing the overall permeability: the passive and the active arms. Overall, thorough mechanistic understanding of the various factors involved in the solubility-permeability interplay may allow developing better solubility-enabling formulations, thereby exploiting the advantages analyzed in this article, offering oral delivery solution even for BCS class IV drugs.

Regional Intestinal Permeability in Rats: A Comparison of Methods

Currently, the screening of new drug candidates for intestinal permeation is typically based on in vitro models which give no information regarding regional differences along the gut. When evaluation of intestinal permeability by region is undertaken, two preclinical rat models are commonly used, the Ussing chamber method and single-pass intestinal perfusion (SPIP). To investigate the robustness of in vivo predictions of human intestinal permeability, a set of four model compounds was systematically investigated in both these models, using tissue specimens and segments from the jejunum, ileum, and colon of rats from the same genetic strain. The influence of luminal pH was also determined at two pH levels. Ketoprofen had high and enalaprilat had low effective (P_eff) and apparent (P_app) permeability in all three regions and at both pH levels. Metoprolol had high P_eff in all regions and at both pHs and high P_app at both pHs and in all regions except the jejunum, where P_app was low. Atenolol had low P_eff in all regions and at both pHs, but had high P_app at pH 6.5 and low P_app at pH 7.4. There were good correlations between these rat in situ P_eff (SPIP) and human in vivo P_eff determined previously for the same compounds by both intestinal perfusion of the jejunum and regional intestinal dosing. The results of this study indicate that both investigated models are suitable for determining the regional permeability of the intestine; however, the SPIP model seems to be the more robust and accurate regional permeability model.

Understanding Drug Release Data through Thermodynamic Analysis

Understanding the factors that can modify the drug release profile of a drug from a Drug-Delivery-System (DDS) is a mandatory step to determine the effectiveness of new therapies. The aim of this study was to assess the Amphotericin-B (AmB) kinetic release profiles from polymeric systems with different compositions and geometries and to correlate these profiles with the thermodynamic parameters through mathematical modeling. Film casting and electrospinning techniques were used to compare behavior of films and fibers, respectively. Release profiles from the DDSs were performed, and the mathematical modeling of the data was carried out. Activation energy, enthalpy, entropy and Gibbs free energy of the drug release process were determined. AmB release profiles showed that the relationship to overcome the enthalpic barrier was PVA-fiber > PVA-film > PLA-fiber > PLA-film. Drug release kinetics from the fibers and the films were better fitted on the Peppas-Sahlin and Higuchi models, respectively. The thermodynamic parameters corroborate these findings, revealing that the AmB release from the evaluated systems was an endothermic and non-spontaneous process. Thermodynamic parameters can be used to explain the drug kinetic release profiles. Such an approach is of utmost importance for DDS containing insoluble compounds, such as AmB, which is associated with an erratic bioavailability.

Biowaiver Monographs for Immediate-Release Solid Oral Dosage Forms: Enalapril

Literature data relevant to the decision to allow a waiver of in vivo bioequivalence testing for the marketing authorization of immediate-release, solid oral dosage forms containing enalapril maleate are reviewed. Enalapril, a prodrug, is hydrolyzed by carboxylesterases to the active angiotensin-converting enzyme inhibitor enalaprilat. Enalapril as the maleate salt is shown to be highly soluble, but only 60%-70% of an orally administered dose of enalapril is absorbed from the gastrointestinal tract into the enterocytes. Consequently, enalapril maleate is a Biopharmaceutics Classification System class III substance. Because in situ conversion of the maleate salt to the sodium salt is sometimes used in production of the finished drug product, not every enalapril maleate-labeled finished product actually contains the maleate salt. Enalapril is not considered to have a narrow therapeutic index. With this background, a biowaiver-based approval procedure for new generic products or after major revisions to existing products is deemed acceptable, provided the in vitro dissolution of both test and reference preparation is very rapid (at least 85% within 15 min at pH 1.2, 4.5, and 6.8). Additionally, the test and reference product must contain the identical active drug ingredient.

Compositional effect of complex biorelevant media on the crystallization kinetics of an active pharmaceutical ingredient

Bile salts impact crystal nucleation and growth of supersaturated solutions of poorly water soluble drugs.

Current and evolving approaches for improving the oral permeability of BCS Class III or analogous molecules

The Biopharmaceutics Classification System (BCS) classifies pharmaceutical compounds based on their aqueous solubility and intestinal permeability. The BCS Class III compounds are hydrophilic molecules (high aqueous solubility) with low permeability across the biological membranes. While these compounds are pharmacologically effective, poor absorption due to low permeability becomes the rate-limiting step in achieving adequate bioavailability. Several approaches have been explored and utilized for improving the permeability profiles of these compounds. The approaches include traditional methods such as prodrugs, permeation enhancers, ion-pairing, etc., as well as relatively modern approaches such as nanoencapsulation and nanosizing. The most recent approaches include a combination/hybridization of one or more traditional approaches to improve drug permeability. While some of these approaches have been extremely successful, i.e. drug products utilizing the approach have progressed through the USFDA approval for marketing; others require further investigation to be applicable. This article discusses the commonly studied approaches for improving the permeability of BCS Class III compounds.

Striking the Optimal Solubility-Permeability Balance in Oral Formulation Development for Lipophilic Drugs: Maximizing Carbamazepine Blood Levels

The purpose of this research was to investigate the performance of cosolvent based solubility-enabling formulations in oral delivery of lipophilic drugs, accounting for the gastrointestinal tract (GIT) luminal solubilization processes, the solubility-permeability interplay, and the overall in vivo systemic absorption. The poorly soluble antiepileptic agent carbamazepine was formulated in three cosolvent-based formulations: 20%, 60%, and 100% PEG-400, and the apparent solubility and rat permeability of the drug in these formulations were evaluated. The performance of the formulations in the dynamic GIT environment was assessed utilizing the biorelevant pH-dilution method. Then, the overall in vivo drug exposure was investigated following oral administration to rats. The three formulations showed dramatic solubility and permeability differences; the 100% PEG-400 provided the highest solubility enhancement and the 20% the poorest, while the exact opposite was evident from the permeability point of view. The dissolution results indicated that the 20% PEG-400 formulation crashes quickly following oral administration, but both the 60% and the 100% PEG-400 formulations allowed full solubilization of the dose throughout the entire GIT-like journey. The best in vivo performing formulation was the 60% PEG-400 (F_sys > 90%), followed by the 100% PEG-400 (F_sys = 76%), and the 20% PEG-400 formulation (F_sys ≈ 60%). In conclusion, this work demonstrates the in vivo solubility-permeability trade-off in oral delivery of lipophilic drugs; when a solubility-enabling formulation is developed, minimal threshold solubility should be targeted, that is just enough to allow solubilization of the drug dose throughout the GIT, while excess solubilizer should be avoided.

Current Development of Anti-Cancer Drug S-1

S-1 is a novel oral fluoropyrimidine derivative, widely used for treating gastric, pancreatic, lung, head, neck and breast carcinomas. It is designed to enhance the clinical utility of an oral fluoropyrimidine and is associated with low gastrointestinal toxicity. S-1 consists of three pharmacological agents (at a molar ratio of 1:0.4:1)-Tegafur (FT), a prodrug of 5-Fluorouracil (5-FU), 5-Chloro-2-4-Dihydroxypyridine (CDHP), which inhibits the activity of Dihydropyrimidine Dehydrogenase (DPD) and Oxonic Acid (Oxo), which reduces Gastrointestinal (GI) toxicity of 5-FU. The present article reviews the current development of clinical study of S-1.

Hydrotropic Solubilization of Lipophilic Drugs for Oral Delivery: The Effects of Urea and Nicotinamide on Carbamazepine Solubility-Permeability Interplay

Hydrotropy refers to increasing the water solubility of otherwise poorly soluble compound by the presence of small organic molecules. While it can certainly increase the apparent solubility of a lipophilic drug, the effect of hydrotropy on the drugs’ permeation through the intestinal membrane has not been studied. The purpose of this work was to investigate the solubility–permeability interplay when using hydrotropic drug solubilization. The concentration-dependent effects of the commonly used hydrotropes urea and nicotinamide, on the solubility and the permeability of the lipophilic antiepileptic drug carbamazepine were studied. Then, the solubility–permeability interplay was mathematically modeled, and was compared to the experimental data. Both hydrotropes allowed significant concentration-dependent carbamazepine solubility increase (up to ∼30-fold). A concomitant permeability decrease was evident both in vitro and in vivo (∼17-fold for nicotinamide and ∼9-fold for urea), revealing a solubility–permeability tradeoff when using hydrotropic drug solubilization. A relatively simplified simulation approach based on proportional opposite correlation between the solubility increase and the permeability decrease at a given hydrotrope concentration allowed excellent prediction of the overall solubility–permeability tradeoff. In conclusion, when using hydrotropic drug solubilization it is prudent to not focus solely on solubility, but to account for the permeability as well; achieving optimal solubility–permeability balance may promote the overall goal of the formulation to maximize oral drug exposure.

Inventory of oral anticancer agents: Pharmaceutical formulation aspects with focus on the solid dispersion technique

Dissolution from the pharmaceutical formulation is a prerequisite for complete and consistent absorption of any orally administered drug, including anticancer agents (oncolytics). Poor dissolution of an oncolytic can result in low oral bioavailability, high variability in blood concentrations and with that suboptimal or even failing therapy. This review discusses pharmaceutical formulation aspects and absorption pharmacokinetics of currently licensed orally administered oncolytics. In nearly half of orally dosed oncolytics poor dissolution is likely to play a major role in low and unpredictable absorption. Dissolution-limited drug absorption can be improved with a solid dispersion which is a formulation method that induces super-saturated drug dissolution and with that it enhances in vivo absorption. This review discusses formulation principles with focus on the solid dispersion technology and how it works to enhance drug absorption. There are currently three licensed orally dosed oncolytics formulated as a solid dispersion (everolimus, vemurafenib and regorafenib) and these formulations result in remarkably improved dissolution and absorption compared to what can be achieved with conventional formulations of the respective oncolytics. Because of the successful implementation of these three solid dispersion formulations, we encourage the application of this formulation method for poorly soluble oral oncolytics.

The solubility-permeability interplay and oral drug formulation design: Two heads are better than one

Poor aqueous solubility is a major challenge in today's biopharmaceutics. While solubility-enabling formulations can significantly increase the apparent solubility of the drug, the concomitant effect on the drug's apparent permeability has been largely overlooked. The mathematical equation to describe the membrane permeability of a drug comprises the membrane/aqueous partition coefficient, which in turn is dependent on the drug's apparent solubility in the GI milieu, suggesting that the solubility and the permeability are closely related, exhibit a certain interplay between them, and treating the one irrespectively of the other may be insufficient. In this article, an overview of this solubility-permeability interplay is provided, and the available data is analyzed in the context of the effort to maximize the overall drug exposure. Overall, depending on the type of solubility-permeability interplay, the permeability may decrease, remain unchanged, and even increase, in a way that may critically affect the formulation capability to improve the overall absorption. Therefore, an intelligent design of solubility-enabling formulation needs to consider both the solubility afforded by the formulation and the permeability in the new luminal environment resulting from the formulation.

Caco-2 Cells, Biopharmaceutics Classification System (BCS) and Biowaiter

Almost all orally administered drugs are absorbed across the intestinal mucosa. The Caco-2 monolayers are used as an in vitro model to predict drug absorption in humans and to explore mechanism of drug absorption. The Caco-2 cells are derived from a human colon adenocarcinoma and spontaneously differentiate to form confluent monolayer of polarized cells structurally and functionally resembling the small intestinal epithelium. For studying drug permeability, Caco-2 cells are seeded onto the Transwell inserts with semipermeable membrane and grown to late confluence (21 days). After determination of cell viability, the integrity of monolayer is checked by phenol red permeability and by 14C-mannitol permeability. The transport from apical to basolateral (AP-BL) and basolateral to apical (BL-AP) is studied by adding the diluted drug on the apical or basolateral side and withdrawing the samples from the opposite compartment, respectively, for HPLC analysis or liquid scintillation spectrometry. Ca2+- free transport medium is used to determine paracellular component of the drug transport. On the basis of permeability and solubility, drugs can be categorized into four classes of Biopharmaceutics Classification System (BCS). For certain drugs, the BCS-based biowaiver approach can be used which enables to reduce in vivo bioequivalence studies.

In Silico Modeling of Gastrointestinal Drug Absorption: Predictive Performance of Three Physiologically Based Absorption Models

Gastrointestinal (GI) drug absorption is a complex process determined by formulation, physicochemical and biopharmaceutical factors, and GI physiology. Physiologically based in silico absorption models have emerged as a widely used and promising supplement to traditional in vitro assays and preclinical in vivo studies. However, there remains a lack of comparative studies between different models. The aim of this study was to explore the strengths and limitations of the in silico absorption models Simcyp 13.1, GastroPlus 8.0, and GI-Sim 4.1, with respect to their performance in predicting human intestinal drug absorption. This was achieved by adopting an a priori modeling approach and using well-defined input data for 12 drugs associated with incomplete GI absorption and related challenges in predicting the extent of absorption. This approach better mimics the real situation during formulation development where predictive in silico models would be beneficial. Plasma concentration-time profiles for 44 oral drug administrations were calculated by convolution of model-predicted absorption-time profiles and reported pharmacokinetic parameters. Model performance was evaluated by comparing the predicted plasma concentration-time profiles, Cmax, tmax, and exposure (AUC) with observations from clinical studies. The overall prediction accuracies for AUC, given as the absolute average fold error (AAFE) values, were 2.2, 1.6, and 1.3 for Simcyp, GastroPlus, and GI-Sim, respectively. The corresponding AAFE values for Cmax were 2.2, 1.6, and 1.3, respectively, and those for tmax were 1.7, 1.5, and 1.4, respectively. Simcyp was associated with underprediction of AUC and Cmax; the accuracy decreased with decreasing predicted fabs. A tendency for underprediction was also observed for GastroPlus, but there was no correlation with predicted fabs. There were no obvious trends for over- or underprediction for GI-Sim. The models performed similarly in capturing dependencies on dose and particle size. In conclusion, it was shown that all three software packages are useful to guide formulation development. However, as a consequence of the high fraction of inaccurate predictions (prediction error >2-fold) and the clear trend toward decreased accuracy with decreased predicted fabs observed with Simcyp, the results indicate that GI-Sim and GastroPlus perform better than Simcyp in predicting the intestinal absorption of the incompletely absorbed drugs when a higher degree of accuracy is needed. In addition, this study suggests that modeling and simulation research groups should perform systematic model evaluations using their own input data to maximize confidence in model performance and output.

NANEX: Process design and optimization

Previously, we introduced a one-step nano-extrusion (NANEX) process for transferring aqueous nano-suspensions into solid formulations directly in the liquid phase. Nano-suspensions were fed into molten polymers via a side-feeding device and excess water was eliminated via devolatilization. However, the drug content in nano-suspensions is restricted to 30 % (w/w), and obtaining sufficiently high drug loadings in the final formulation requires the processing of high water amounts and thus a fundamental process understanding. To this end, we investigated four polymers with different physicochemical characteristics (Kollidon(®) VA64, Eudragit(®) E PO, HPMCAS and PEG 20000) in terms of their maximum water uptake/removal capacity. Process parameters as throughput and screw speed were adapted and their effect on the mean residence time and filling degree was studied. Additionally, one-dimensional discretization modeling was performed to examine the complex interactions between the screw geometry and the process parameters during water addition/removal. It was established that polymers with a certain water miscibility/solubility can be manufactured via NANEX. Long residence times of the molten polymer in the extruder and low filling degrees in the degassing zone favored the addition/removal of significant amounts of water. The residual moisture content in the final extrudates was comparable to that of extrudates manufactured without water.

Excised segments of rat small intestine in Ussing chamber studies: A comparison of native and stripped tissue viability and permeability to drugs

Excised rat intestinal tissue mounted in an Ussing chamber can be used for intestinal permeability assessments in drug development. The outer layer of the intestine, the serosa and part of the muscle layer, is traditionally removed since it is considered a barrier to the diffusion of nutrients and oxygen as well as to that of pharmaceutical substances. However, the procedure for removing the serosal-muscle layer, i.e. stripping, is a technically challenging process in the pre-experimental preparation of the tissue which may result in tissue damage and reduced viability of the segment. In this study, the viability of stripped and native (non-stripped) rat small intestine tissue segments mounted in Ussing chambers was monitored and the apparent permeability of the tissue to a set of test compounds across both tissue preparations was determined. Electrical measurements, in particular the potential difference (PD) across the intestinal membrane, were used to evaluate the viability. In this study, there were no differences in initial PD (health status of the tissue) or PD over time (viability throughout the experiment) between native and stripped rat jejunum segments. Overall, there were also no significant differences in permeability between stripped and native rat intestinal tissue for the compounds in this study. Based on these results, we propose that stripping can be excluded from the preparation procedures for rat jejunal tissue for permeability studies when using the Ussing chamber technique.

Intestinal solubility and absorption of poorly water soluble compounds: predictions, challenges and solutions

We have explored for which type of compounds biorelevant dissolution profiling in simulated intestinal fluids would accurately predict solubility in human intestinal fluid. In total, 474 solubility values in simulated and aspirated human intestinal fluid for 78 drugs were compiled and analyzed. Significant solubilization in the colloidal structures was obtained in fasted and fed state fluids for drug compounds with a logD(oct)>3. Highly lipophilic compounds with high melting points (Tm > 200 °C) could also be significantly solubilized, but typically such compounds had solubility values in the lower µg/ml range also in the presence of the colloidal structures. On the basis of our analysis, compounds with a logD(oct)>3 should be explored in biorelevant dissolution media to better predict in vivo performance after oral dosing.

The Effect of Excipients on the Permeability of BCS Class III Compounds and Implications for Biowaivers

Purpose

Currently, the FDA allows biowaivers for Class I (high solubility and high permeability) and Class III (high solubility and low permeability) compounds of the Biopharmaceutics Classification System (BCS). Scientific evidence should be provided to support biowaivers for BCS Class I and Class III (high solubility and low permeability) compounds.

Methods

Data on the effects of excipients on drug permeability are needed to demonstrate that commonly used excipients do not affect the permeability of BCS Class III compounds, which would support the application of biowaivers to Class III compounds. This study was designed to generate such data by assessing the permeability of four BCS Class III compounds and one Class I compound in the presence and absence of five commonly used excipients.

Results

The permeability of each of the compounds was assessed, at three to five concentrations, with each excipient in two different models: Caco-2 cell monolayers, and in situ rat intestinal perfusion. No substantial increases in the permeability of any of the compounds were observed in the presence of any of the tested excipients in either of the models, with the exception of disruption of Caco-2 cell monolayer integrity by sodium lauryl sulfate at 0.1 mg/ml and higher.

Conclusion

The results suggest that the absorption of these four BCS Class III compounds would not be greatly affected by the tested excipients. This may have implications in supporting biowaivers for BCS Class III compounds in general.

Applications of Fluorine in Medicinal Chemistry

The role of fluorine in drug design and development is expanding rapidly as we learn more about the unique properties associated with this unusual element and how to deploy it with greater sophistication. The judicious introduction of fluorine into a molecule can productively influence conformation, pKa, intrinsic potency, membrane permeability, metabolic pathways, and pharmacokinetic properties. In addition, (18)F has been established as a useful positron emitting isotope for use with in vivo imaging technology that potentially has extensive application in drug discovery and development, often limited only by convenient synthetic accessibility to labeled compounds. The wide ranging applications of fluorine in drug design are providing a strong stimulus for the development of new synthetic methodologies that allow more facile access to a wide range of fluorinated compounds. In this review, we provide an update on the effects of the strategic incorporation of fluorine in drug molecules and applications in positron emission tomography.

The use of captisol (SBE7-β-CD) in oral solubility-enabling formulations: Comparison to HPβCD and the solubility-permeability interplay

The aim of this research was to study the interaction of sulfobutyl ether7 β-cyclodextrin (captisol) and 2-hydroxypropyl-β-cyclodextrin (HPβCD) with the poorly soluble antiarrhythmic drug amiodarone, and to investigate the consequent solubility-permeability interplay. Phase-solubility studies of amiodarone with the two cyclodextrins, followed by PAMPA and rat intestinal permeability experiments, were carried out, and the solubility-permeability interplay was then illustrated as a function of increasing cyclodextrin content. Equimolar levels of captisol allowed ∼10-fold higher amiodarone solubility than HPβCD, as well as binding constant. With both captisol and HPβCD, decreased in vitro and in vivo amiodarone apparent permeability was evident with increasing CD levels and increased apparent solubility. A theoretical model assuming direct proportionality between the apparent solubility increase allowed by the CD and permeability decrease was able to accurately predict the solubility-permeability tradeoff as a function of CD levels. In conclusion, the addition of ionic interactions (e.g. amiodarone-captisol) to hydrophobic interactions of the inclusion complex formation may result in synergic effect on solubilization; however, it is not merely the solubility that should be examined when formulating an oral poorly soluble compound, but the solubility-permeability balance, in order to maximize the overall drug exposure.