A Systematic Study of Molecular Interactions of Anionic Drugs with a Dimethylaminoethyl Methacrylate Copolymer Regarding Solubility Enhancement

A study of hydrophobic domain formation of polymeric drug precipitation inhibitors in aqueous solution

Despite the widespread use of polymers as precipitation inhibitors in supersaturating drug formulations, the current understanding of their mechanisms of action is still incomplete. Specifically, the role of hydrophobic drug interactions with polymers by considering possible supramolecular conformations in aqueous dispersion is an interesting topic. Accordingly, this study investigated the tendency of polymers to create hydrophobic domains, where lipophilic compounds may nest to support drug solubilisation and supersaturation. Fluorescence spectroscopy with the environment-sensitive probe pyrene was compared with atomistic molecular dynamics simulations of the model drug fenofibrate (FENO). Subsequently, kinetic drug supersaturation and thermodynamic solubility experiments were conducted. As a result, the different polymers showed hydrophobic domain formation to a varying degree and the molecular simulations supported interpretation of fluorescence spectroscopy data. Molecular insights were gained into the conformational structure of how the polymers interacted with FENO in solution phase, which apart from nucleation and crystal growth effects, determined drug concentrations in solution. Notable was that even at the lowest polymer concentration of 0.01 %, w/v, there were polymer-specific solubilisation effects of FENO observed and the resulting reduction in apparent drug supersaturation provided relevant knowledge both from a mechanistic and practical perspective.

Development of raft-forming liquid formulations loaded with ginger extract-solid dispersion for treatment of gastric ulceration

Raft-forming liquid formulations incorporating ginger extract solid dispersion (GE-SD) were developed to achieve prolonged delivery of 6-gingerol in the stomach and thus increase the effectiveness of gastric ulcer treatment. The solubility of 6-gingerol in 0.1 N HCl (pH 1.2) was maximized (15 mg/mL) by combining ginger extract with PVP K30 at 1:3 w/w ratio to produce a solid dispersion. The nature of GE-SD was confirmed by PXRD and FT-IR analysis. PXRD pattern showed miscibility of GE and PVP K30 in amorphous solid dispersion and the FT-IR spectra confirmed the formation of hydrogen bond between GE and PVP K30. GE-SD-loaded raft-forming liquids were prepared using sodium alginate as a gel former and HPMC as a release-controlling agent. The formulations exhibited rapid floating behavior in 0.1 N HCl (<30 s) and remained afloat on the surface over 8 h. The formed raft structures provided sufficient strength (>7.5 g) and allowed sustained release of more than 70 % of the 6-gingerol content over 8 h in 0.1 N HCl. Raft-forming formulations incorporating ginger extract demonstrated anti-inflammatory activity by inhibiting nitric oxide production in LPS-stimulated RAW 264.7 macrophage cells (IC50 = 5.13 ± 0.07 μg/mL). Exposure to the formulations also had a significant cytotoxic effect on AGS human gastric adenocarcinoma cells with an IC50 of 17.45 ± 0.29 μg/mL. In addition, the raft-forming formulations enhanced the migratory behavior of L929 mouse fibroblasts in the scratch wound model. Taken together, these findings reveal the benefits of gastro-retentive, GE-SD-loaded raft-forming liquid formulations for improving the treatment of gastric ulcers.

Poly(vinylpyridine-co-vinylpyridine N-oxide) Excipients Mediate Rapid Dissolution and Sustained Supersaturation of Posaconazole Amorphous Solid Dispersions

The chemical structure of excipients molecularly mixed in an amorphous solid dispersion (ASD) has a significant impact on properties of the ASD including dissolution behavior, physical stability, and bioavailability. Polymers used in ASDs require a balance between hydrophobic and hydrophilic functionalities to ensure rapid dissolution of the amorphous dispersion as well as sustained supersaturation of the drug in solution. This work demonstrates the use of postpolymerization functionalization of poly(vinylpyridine) excipients to elucidate the impact of polymer properties on the dissolution behavior of amorphous dispersions containing posaconazole. It was found that N-oxidation of pyridine functionalities increased the solubility of poly(vinylpyridine) derivatives in neutral aqueous conditions and allowed for nanoparticle formation which supplied posaconazole into solution at concentrations exceeding those achieved by more conventional excipients such as hydroxypropyl methylcellulose acetate succinate (HPMCAS) or Eudragit E PO. By leveraging these functional modifications of the parent poly(vinylpyridine) excipient to increase polymer hydrophilicity and minimize the effect of polymer on pH, a new polymeric excipient was optimized for rapid dissolution and supersaturation maintenance for a model compound.

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.

Effect of Drug-Polymer Interaction in Amorphous Solid Dispersion on the Physical Stability and Dissolution of Drugs: The Case of Alpha-Mangostin

Improving drug solubility is necessary for formulations of poorly water-soluble drugs, especially for oral administration. Amorphous solid dispersions (ASDs) are widely used in the pharmaceutical industry to improve the physical stability and solubility of drugs. Therefore, this study aims to characterize interaction between a drug and polymer in ASD, as well as evaluate the impact on the physical stability and dissolution of alpha-mangostin (AM). AM was used as a model of a poorly water-soluble drug, while polyvinylpyrrolidone (PVP) and eudragit were used as polymers. The amorphization of AM-eudragit and AM-PVP was confirmed as having a halo pattern with powder X-ray diffraction measurements and the absence of an AM melting peak in the differential scanning calorimetry (DSC) curve. The solubility of amorphous AM increased in the presence of either eudragit or PVP due to amorphization and interactions of AM-polymer. Furthermore, FT-IR spectroscopy and in silico studies revealed hydrogen bond interactions between the carbonyl group of AM and the proton of eudragit as well as PVP. AM-eudragit with a ratio of 1:1 recrystallized after 7 days of storage at 25 °C and 90% RH, while the AM-PVP 1:4 and 1:10 samples retained the X-ray halo patterns, even under humid conditions. In a dissolution test, the presence of polymer in ASD significantly improved the dissolution profile due to the intermolecular interaction of AM-polymer. AM-eudragit 1:4 maintained AM supersaturation for a longer time compared to the 1:1 sample. However, a high supersaturation was not achieved in AM-PVP 1:10 due to the formation of large agglomerations, leading to a slow dissolution rate. Based on the results, interaction of AM-polymer in ASD can significantly improve the pharmaceutical properties of AM including the physical stability and dissolution.

Biorelevant Dissolution Method Considerations for the Appropriate Evaluation of Amorphous Solid Dispersions: are Two Stages Necessary?

Biorelevant dissolution testing has been widely used to better understand a drug or formulation's behavior in the human gastrointestinal (GI) tract. The successful evaluation of biorelevant dissolution behavior requires recognizing the importance of utilizing suitable biorelevant media in conjunction with an appropriate dissolution method, especially for supersaturating drug delivery systems, such as amorphous solid dispersions (ASDs). However, most conventional biorelevant dissolution testing methods are not able to accurately reflect the dissolution, supersaturation, and precipitation tendencies of a drug or formulation, which could misinform ASD formulation screening and optimization. In this study, we developed a single compartment 2-stage pH-shift dissolution testing method to simulate the changes in pH, media composition, and transit time in the GI tract, and results were compared against the conventional single compartment 1-stage dissolution method. Nine model drugs were selected based on their ionization properties (i.e. acid, base or neutral) and precipitation tendency (i.e. moderate or slow crystallizer). The dissolution results confirmed that 2-stage pH-shift dissolution is the preferred biorelevant dissolution method to assess non-ionized weak base (nifedipine) and neutral (griseofulvin) compounds exhibiting a moderate precipitation rate from solution when formulated as ASDs. Finally, we designed a flowchart guidance for the appropriate biorelevant dissolution performance characterization of different categories of ASD formulations.

Dissolution Behavior of Weakly Basic Pharmaceuticals from Amorphous Dispersions Stabilized by a Poly(dimethylaminoethyl Methacrylate) Copolymer

Amorphous solid dispersions (ASDs) are a well-documented formulation approach to improve the rate and extent of dissolution for hydrophobic pharmaceuticals. However, weakly basic compounds can complicate standard approaches to ASDs due to pH-dependent solubility, resulting in uncontrolled drug release in gastric conditions and unstabilized supersaturated solutions prone to precipitation at neutral pH. This work examines the release mechanisms of amorphous dispersions containing model weakly basic pharmaceuticals posaconazole and lumefantrine from a basic poly(dimethylaminoethyl methacrylate) copolymer (Eudragit EPO) and compares their dissolution behavior with ASDs stabilized by acidic and neutral polymers to understand potential benefits to release from a basic polymeric stabilizer. It was found that dissolution of Eudragit EPO ASDs resulted in supersaturation under gastric conditions, which could be sustained upon adjustment to neutral pH. However, the dissolution behavior of Eudragit EPO ASDs was sensitive to the initial pH of the gastric media. For lumefantrine, elevated initial gastric pH resulted in precipitation of amorphous nanoparticles; for posaconazole, elevated gastric pH led to crystallization of the pharmaceutical from solution. This sensitivity to gastric pH was found to originate from the impact of Eudragit EPO on gastric pH and the solubility of each pharmaceutical in the first stage of dissolution. In total, these data illustrate benefits and liabilities for the use of Eudragit EPO for ASDs containing weak pharmaceutical bases to guide the design of robust pharmaceutical formulations.

Niclosamide-loaded nanoparticles disrupt Candida biofilms and protect mice from mucosal candidiasis

Candida albicans biofilms are a complex multilayer community of cells that are resistant to almost all classes of antifungal drugs. The bottommost layers of biofilms experience nutrient limitation where C. albicans cells are required to respire. We previously reported that a protein Ndu1 is essential for Candida mitochondrial respiration; loss of NDU1 causes inability of C. albicans to grow on alternative carbon sources and triggers early biofilm detachment. Here, we screened a repurposed library of FDA-approved small molecule inhibitors to identify those that prevent NDU1-associated functions. We identified an antihelminthic drug, Niclosamide (NCL), which not only prevented growth on acetate, C. albicans hyphenation and early biofilm growth, but also completely disengaged fully grown biofilms of drug-resistant C. albicans and Candida auris from their growth surface. To overcome the suboptimal solubility and permeability of NCL that is well known to affect its in vivo efficacy, we developed NCL-encapsulated Eudragit EPO (an FDA-approved polymer) nanoparticles (NCL-EPO-NPs) with high niclosamide loading, which also provided long-term stability. The developed NCL-EPO-NPs completely penetrated mature biofilms and attained anti-biofilm activity at low microgram concentrations. NCL-EPO-NPs induced ROS activity in C. albicans and drastically reduced oxygen consumption rate in the fungus, similar to that seen in an NDU1 mutant. NCL-EPO-NPs also significantly abrogated mucocutaneous candidiasis by fluconazole-resistant strains of C. albicans, in mice models of oropharyngeal and vulvovaginal candidiasis. To our knowledge, this is the first study that targets biofilm detachment as a target to get rid of drug-resistant Candida biofilms and uses NPs of an FDA-approved nontoxic drug to improve biofilm penetrability and microbial killing.

Development of starch/chitosan expandable films as a gastroretentive carrier for ginger extract-loaded solid dispersion

Gastroretentive expandable films were developed to provide controlled release of ginger extract (GE) for treatment of gastric diseases. The dosage form consisted of ginger extract solid dispersion (GE-SD) loaded in a starch/chitosan composite film, which was subsequently folded and inserted into a hard gelatin capsule. GE-SD was prepared by solvent evaporation using an optimum weight ratio of 1:1 for GE and PVP K30. Expandable films containing GE-SD were prepared by solvent casting combinations of chitosan and either rice-, glutinous rice - or pregelatinized maize starch with glycerin incorporated as a plasticizer. The optimized film formulation prepared from glutinous rice starch, exhibited tensile strength of 5.4 N/cm² and high expansion in simulated gastric fluid (SGF), resulting in a 2.8-fold increase in area. The films resulted in sustained release of up to 90% of the content of 6-gingerol during 8 h exposure to SGF. Furthermore, the 6-gingerol released from the film displayed dose-dependent cytotoxic activity against AGS human gastric adenocarcinoma cells and anti-inflammatory activity by inhibiting the production of nitric oxide (NO) in LPS-stimulated RAW264.7 cells.

Nanostructure and Molecular-Level Characterization of Aminoalkyl Methacrylate Copolymer and the Impact on Drug Solubilization Ability

The effects of pH changes and saccharin (SAC) addition on the nanostructure and mobility of the cationic aminoalkyl methacrylate copolymer Eudragit E PO (EUD-E) and its drug solubilization ability were investigated. Small-angle X-ray scattering performed using synchrotron radiation and atomic force microscopy showed that the EUD-E nanostructure, which has a size of approximately several nanometers, changed from a random coil structure at low pH (pH 4.0-5.0) to a partially folded structure at high pH (pH 5.5-6.5). The EUD-E also formed a partially folded structure in a wide pH range of 4.5-6.5 when SAC was present, and the coil-to-globule transition was moderate with pH increase, compared with that when SAC was absent. The equilibrium solubility of the neutral drug naringenin (NAR) was enhanced in the EUD-E solution and further increased as the pH increased. The enlargement of the hydrophobic region of EUD-E in association with the coil-to-globule transition led to efficient solubilization of NAR. The interaction with SAC enhanced the mobility of the EUD-E chains in the hydrophobic region of EUD-E, resulting in changes in the drug-solubilizing ability. ¹H high-resolution magic-angle spinning NMR measurements revealed that the solubilized NAR in the partially folded structure of EUD-E showed higher molecular mobility in the presence of SAC than in the absence of SAC. This study highlighted that solution pH and the presence of SAC significantly changed the drug solubilization ability of EUD-E, followed by changes in the EUD-E nanostructure, including its hydrophobic region.

[Solid State NMR Investigation for Molecular States of Specialized Formulation to Improve the Water Solubility of Poorly Water-soluble Drugs]

70-90% of recently developed new drug candidates are poorly soluble in water, which creates a series of thorny challenges in developing its oral dosage forms, resulting in low bioavailability. In pre-formulation study, various specialized formulations have been developed to improve drug solubility. Intermolecular interactions between drug and excipients in the formulations can modify the drug state and achieve the improvement of drug solubility. Therefore, the understanding of intermolecular interaction is essential to design formulations with higher quality and to assure the quality as a pharmaceutical product. Solid-state NMR has attracted much attention as a promising method to evaluate the molecular state of a drug and the interaction between a drug and excipient in its formulation. I have applied solid-state NMR and its characteristic technique, namely magic-angle spinning (MAS), for various specialized formulations including amorphous solid dispersion, supersaturated solution, drug-loaded organic nanotube, and drug nanosuspension. The intermolecular interactions of drug and excipient in amorphous solid dispersion have been identified by ¹³C and ¹⁵N solid-state NMR. High-resolution MAS determined the interaction modes of drug and excipient in a supersaturated solution. The two-step dissolution profile of drug from organic nanotube was understood, based on the molecular states revealed by the combination of various solid-state NMR techniques. A suspended-state NMR clarified the nanostructure of drug nanoparticles dispersed in water. It is expected that more qualified pharmaceutical formulations with improved drug solubility can be designed based on the remarkable development of recent solid-state NMR technology.

Drug-Rich Phases Induced by Amorphous Solid Dispersion: Arbitrary or Intentional Goal in Oral Drug Delivery?

Among many methods to mitigate the solubility limitations of drug compounds, amorphous solid dispersion (ASD) is considered to be one of the most promising strategies to enhance the dissolution and bioavailability of poorly water-soluble drugs. The enhancement of ASD in the oral absorption of drugs has been mainly attributed to the high apparent drug solubility during the dissolution. In the last decade, with the implementations of new knowledge and advanced analytical techniques, a drug-rich transient metastable phase was frequently highlighted within the supersaturation stage of the ASD dissolution. The extended drug absorption and bioavailability enhancement may be attributed to the metastability of such drug-rich phases. In this paper, we have reviewed (i) the possible theory behind the formation and stabilization of such metastable drug-rich phases, with a focus on non-classical nucleation; (ii) the additional benefits of the ASD-induced drug-rich phases for bioavailability enhancements. It is envisaged that a greater understanding of the non-classical nucleation theory and its application on the ASD design might accelerate the drug product development process in the future.

Hybrid natural hydrogels integrated with voriconazole-loaded microspheres for ocular antifungal applications

Fungal keratitis is a major threat to ocular morbidity and blindness. The therapeutic efficacy of eye drops against fungal keratitis is limited by their poor bioavailability, especially in patients with corneal stromal ulcers that lead to tissue defects. Therefore, intervention measures that can control fungal infection while promoting tissue regeneration are desirable. Herein, we designed and fabricated natural antifungal hydrogels that comprise a decellularized porcine cornea (DPC), gelatin and microspheres (MCs) containing voriconazole (Vor) for the management of fungal keratitis with focal corneal stromal defects. The size and structure of the Vor-loaded MCs were characterized by scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC). The antifungal drug Vor showed that continuous release from the hybrid hydrogel system for up to 7 days and that MCs loading did not affect the mechanical properties, in vitro release profile or cytocompatibility of the hybrid hydrogel. Moreover, the Vor-loaded hydrogels exhibited excellent antifungal properties against F. solani and A. fumigatus. The efficiency of the natural antifungal hydrogel was evaluated by an ex vivo infectious rabbit corneal defect model. After 24 h, the number of fungal colony-forming units (CFU) significantly decreased in antifungal hydrogel-treated corneal tissue compared with that in non-treated corneas and corneas treated with hydrogels without Vor. The above results demonstrated that this natural hydrogel-based drug delivery system holds great promise for preventing fungal keratitis infection while promoting focal corneal stromal regeneration. Additionally, natural hybrid hydrogels might be a candidate material for use with various drugs in the effective treatment of many other ocular diseases.

Porous and highly responsive cross-linked β-cyclodextrin based nanomatrices for improvement in drug dissolution and absorption

AIMS

Aim of the study was to enhance the solubility of Chlorthalidone by developing beta-cyclodextrin cross-linked hydrophilic nanomatrices.

MAIN METHODS

Nine different formulations were fabricated by free radical polymerization technique. All formulations were characterized through different studies. FTIR spectroscopy of unloaded and loaded nanomatrices was processed to determine compatibility of constituents and that of the drug with the system. Surface morphology of the nanomatrices was studied by SEM. The size of the optimized formulation was determined by zeta sizer. Swelling, in-vitro release and solubility studies were carried out in different media and results of in-vitro release profiles of nanomatrices and commercially available tablet of Chlorthalidone were compared. For determination of biocompatibility, toxicity studies were proclaimed in rabbits.

KEY FINDINGS

Main peaks of corresponding functional groups of individual constituents and that of drug were depicted in FTIR spectra of unloaded and loaded nanomatrices. Porous and fluffy structure was visualized through SEM images. Particle size of the optimized formulation was in the range of 175 ± 5.27 nm. Percent loading of optimized formulation showed the best result. Comparing the in-vitro drug release profiles of nanomatrices and commercially available tablet, the results of the synthesized nanomatrices were quite satisfactory. Solubility profiles were also high as compared to the drug alone. Moreover, toxicity studies confirmed that nanomatrices were biocompatible and no sign of any toxic effect was found.

SIGNIFICANCE

We concluded that our developed nanomatrices had successfully enhanced the solubility of Chlorthalidone and can also be used for other poorly aqueous soluble drugs.

The Influence of the Strength of Drug-Polymer Interactions on the Dissolution of Amorphous Solid Dispersions

In an earlier report, ionic interactions between ketoconazole (KTZ), a weakly basic drug, and poly(acrylic acid) (PAA), an anionic polymer, resulted in a dramatic decrease in molecular mobility as well as reduced crystallization propensity of amorphous solid dispersion (ASD) in the solid state. On the other hand, weaker dipole-dipole interactions between KTZ and polyvinylpyrrolidone (PVP) resulted in ASDs with higher crystallization propensity (Mistry Mol Pharm., 2015, 12 (9), 3339-3350). In this work, we investigated the behavior of the ketoconazole (KTZ) solid dispersions in aqueous media. In vitro dissolution tests showed that the PAA ASD maintained the level of supersaturation for a longer duration than the PVP ASD at low polymer contents (4-20% w/w polymer). Additionally, the PAA ASDs were more resistant to drug crystallization in aqueous medium when measured with synchrotron X-ray diffractometry. Two-dimensional ¹H nuclear Overhauser effect spectroscopy (NOESY) NMR cross peaks between ketoconazole and PAA confirmed the existence of drug-polymer interactions in D₂O. The interaction was accompanied by a reduced drug diffusivity as monitored by 2D diffusion ordered spectroscopy (DOSY) NMR and enthalpy-driven when characterized by isothermal titration calorimetry (ITC). On the other hand, drug-polymer interactions were not detected between ketoconazole and PVP in aqueous solution, with NOESY, DOSY, or ITC. The results suggest that interactions that stabilize ASDs in the solid state can also be relevant and important in sustaining supersaturation in solution.

Polymer Type Impacts Amorphous Solubility and Drug-Rich Phase Colloidal Stability: A Mechanistic Study Using Nuclear Magnetic Resonance Spectroscopy

The polymer used in an amorphous solid dispersion (ASD) formulation plays a critical role in dosage form performance. Herein, drug-polymer interactions in aqueous solution were evaluated in order to better understand the dispersion stability of the colloidal drug-rich phase generated when the amorphous solubility is exceeded. The amorphous solubility (S_a,IBP) of ibuprofen (IBP) decreased when hypromellose (HPMC) or polyvinylpyrrolidone/vinyl acetate (PVP-VA) were present in solution. Solution nuclear magnetic resonance (NMR) spectroscopy revealed that a large amount of HPMC and PVP-VA distributed into the IBP-rich phase. The mixing of HPMC and PVP-VA with the IBP-rich phase led to the decreased S_a,IBP. In contrast, the charged amino methacrylate copolymer (Eudragit E PO, EUD-E) showed minimal mixing with the IBP-rich phase; however, this polymer did lead to solubilization of IBP in the bulk aqueous phase. Although the IBP-rich phase generated by dissolving IBP at concentrations above S_a,IBP rapidly coarsened followed by creaming in the absence of polymer, all of the polymers stabilized the IBP dispersion to some extent. The droplet size of the IBP-rich phase immediately after formation was around 300 nm in HPMC and PVP-VA solutions, and around 800 nm in the EUD-E solution. The mixing of the former two polymers with the drug-rich phase is thought to account for the smaller droplet size. Despite a smaller initial size, the dispersion stability of the IBP-rich droplets was relatively poor in the presence of PVP-VA. In contrast, the coalescence of the IBP-rich droplets was effectively suppressed by the steric repulsion and electrostatic repulsion derived from adsorbed HPMC and EUD-E, respectively. The present study highlights the complex effects of a polymer on the drug amorphous solubility and colloidal stability, which should be considered when optimizing ASD formulations with the goal of maximizing drug absorption.

Raft-forming gastro-retentive formulations based on Centella asiatica extract-solid dispersions for gastric ulcer treatment

Liquid raft-forming formulations comprising solid dispersions of glycoside-rich Centella asiatica extract and Eudragit® EPO (GR-SD) were developed to achieve prolonged delivery of the glycosides, asiaticoside (AS) and madecassoside (MS) in the stomach and thus increase the effectiveness of gastric ulcer treatment. Solid dispersions of GR extract and Eudragit® EPO (GR-SD, weight ratio 1:0.5) resulted in the highest solubility of AS (41.7 mg/mL) and MS (29.3 mg/mL) and completed dissolution of both glycosides occurred in SGF within 10 min. The optimized raft-forming formulation was composed of alginate (2%), HPMC K-100 (0.5%), GR-SD (1.2%), and calcium carbonate (0.5%) as a calcium source and carbon dioxide producer. The formulation provided sufficient raft strength (> 7.0 g), rapid floating behavior in SGF (~30 s), and sustained release of AS (more than 80%) and MS (85%) over 8 h. GR-SD-based formulations administered once daily to rats for two days at a dose of 10 mg AS/kg reduced the severity of gastric ulcer induced by indomethacin with a greater curative efficacy than those of unformulated GR extract and a standard antiulcer agent: lansoprazole (p < 0.05). These findings demonstrate that GR-SD-based raft-forming systems offer significant promise for improving the treatment of gastric ulcers induced by non-steroidal anti-inflammatory drugs.

Intermolecular Interactions between Drugs and Aminoalkyl Methacrylate Copolymer in Solution to Enhance the Concentration of Poorly Water-Soluble Drugs

An aminoalkyl methacrylate copolymer, Eudragit^® E (EUD-E), has gained tremendous attention as a solid dispersion carrier because it efficiently stabilizes drugs in the amorphous state. Furthermore, EUD-E remarkably enhances drug dissolution in water. This review focuses on the interaction between drugs and EUD-E in solution, which contributes to the enhancement of drug concentration. Studies examining interactions between acidic drugs and EUD-E in organic solvents have revealed that the interaction occurs predominantly by electrostatic interaction, including hydrogen bonding and dipolar interactions. Other studies on interactions in aqueous solution found evidence for strong electrostatic interactions between acidic drugs and EUD-E in ion exchange experiments. ¹H-NMR studies using high-resolution magic-angle spinning, nuclear Overhauser effect spectroscopy, diffusion, and relaxation time measurements successfully identified the interaction site and strength in aqueous solution. Hydrophobic and ionic interactions occurred between drugs and EUD-E. The conformation of EUD-E, which was affected by the ionic strength and pH of the aqueous media, also influenced the interaction. The knowledge discussed in this review will be helpful in designing solid dispersion formulations with EUD-E, which will efficiently enhance drug concentration and subsequent absorption into the body.

Strategies for Improving Healing of the Gastric Epithelium Using Oral Solid Dispersions Loaded with Pentacyclic Triterpene-Rich Centella Extract

The pentacyclic triterpenoid compounds in Centella asiatica extract, mainly consisting of asiaticoside (AS), asiatic acid (AA), madecassoside (MS), and madecassic acid (MA), possess wound healing and anti-ulcer properties, but their low aqueous solubility and dissolution rate are disadvantageous for oral administration. In this study, pentacyclic triterpene-rich centella extract (PRE) was combined with Eudragit® EPO as a hydrophilic polymer using solvent evaporation to produce a solid dispersion (PRE-ESD). The optimum PRE/Eudragit ratio of 1:2 enhanced the solubility and dissolution of glycosides (AS > 3.5 folds, MS > 2 folds) and aglycones (AA > 65 folds and MA > 56 folds) in 0.1 N hydrochloric acid (pH 1.2). DSC, XRD, and FT-IR analysis showed that the four pentacyclic triterpenes in PRE existed in the amorphous state in the solid dispersion. Moreover, almost 100% of the compounds were released from the solid dispersion within 2 h. The effects of PRE-ESD on cell proliferation and wound healing in vitro were investigated in human gastric epithelial cell lines (AGS cells). Exposure to PRE-ESD (equivalent to PRE concentration of 10 μg/mL) promoted cell proliferation and enhanced 'wound closure' in the scratch assay of wound healing by 82% compared with non-treated groups. Unformulated MA and AA aglycones did not exhibit a wound healing effect. Moreover, PRE-ESD was found to accelerate wound closure compared with either AS or MS, indicating that the wound healing properties of PRE-ESD are conferred by the active compounds AS and MS that are presented in PRE.

Evaluation of Oleic Acid and Polyethylene Glycol Monomethyl Ether Conjugate (PEGylated Oleic Acid) as a Solubility Enhancer of Furosemide

Poor aqueous solubility limits the therapeutic efficacy of many marketed and investigational drugs. Synthesis of new drugs with improved solubility is challenging due to time constraint and expenses involved. Therefore, finding the solubility enhancers for existing drugs is an attractive and profitable strategy. In this study, PEGylated oleic acid (OA-mPEG5000), a conjugate of oleic acid and mPEG5000 was synthesized and evaluated as a solubilizer for furosemide. OA-mPEG5000 was evaluated as a nanocarrier for furosemide by formulating polymersomes. Solubility of furosemide in milli-Q water and aqueous OA-mPEG5000 solution was determined using shake flask method. At 37 °C, the solubility of furosemide in OA-mPEG5000 (1% w/w) and milli-Q water was 3404.7 ± 254.6 µg/mL and 1020.2 ± 40.9 µg/mL, respectively. Results showed there was a 3.34-fold increase in solubility of furosemide in OA-mPEG5000 compared to water at 37 °C. At 25 °C, there was a 3.31-fold increase in solubilization of furosemide in OA-mPEG5000 (1% w/w) (90.0 ± 1.45 µg/mL) compared to milli-Q water (27.2 ± 1.43 µg/mL). Size, polydispersity index and zeta potential of polymersomes ranged from 85–145.5 nm, 0.187–0.511 and −4.0–12.77 mV, respectively. In-vitro release study revealed a burst release (71%) within 1 h. Significant enhancement in solubility and formation of polymersomes suggested that OA-mPEG5000 could be a good solubilizer and nanocarrier for furosemide.

Methacrylate-Copolymer Eudragit EPO as a Solubility-Enabling Excipient for Anionic Drugs: Investigation of Drug Solubility, Intestinal Permeability, and Their Interplay

The purpose of this work was to investigate the use of the dimethylaminoethyl methacrylate-copolymer Eudragit EPO (EPO) in oral solubility-enabling formulations for anionic lipophilic drugs, aiming to guide optional formulation design and maximize oral bioavailability. We have studied the solubility, the permeability, and their interplay, using the low-solubility nonsteroidal anti-inflammatory drug mefenamic acid as a model drug. Then, we studied the biorelevant solubility enhancement of mefenamic acid from EPO-based formulations throughout the gastrointestinal tract (GIT), using the pH-dilution dissolution method. EPO allowed a profound and linear solubility increase of mefenamic acid, from 10 μg/mL without EPO to 9.41 mg/mL in the presence of 7.5% EPO (∼940-fold; 37 °C); however, a concomitant decrease of the drug permeability was obtained, both in vitro and in vivo in rats, indicating a solubility-permeability trade-off. In the absence of an excipient, the unstirred water layer (UWL) adjacent to the GI membrane was found to hinder the permeability of the drug, accounting for this UWL effect and revealing that the true membrane permeability allowed good prediction of the solubility-permeability trade-off as a function of EPO level using a direct relationship between the increased solubility afforded by a given EPO level and the consequent decreased permeability. Biorelevant dissolution studies revealed that EPO levels of 0.05 and 0.1% were insufficient to dissolve mefenamic acid dose during the entire dissolution time course, whereas 0.5 and 1% EPO allowed complete solubility with no drug precipitation. In conclusion, EPO may serve as a potent solubility-enabling excipient for BCS class II/IV acidic drugs; however, it should be used carefully. It is prudent to use the minimal EPO amounts just sufficient to dissolve the drug dose throughout the GIT and not more than that. Excess amounts of EPO provide no solubility gain and cause further permeability loss, jeopardizing the overall success of the formulation. This work may help the formulator to hit the optimal solubility-permeability balance, maximizing the oral bioavailability afforded by the formulation.

Miniaturized Measurement of Drug-Polymer Interactions via Viscosity Increase for Polymer Selection in Amorphous Solid Dispersions

Drug-polymer interactions have a substantial impact on stability and performance of amorphous solid dispersions (ASD) but are difficult to analyze. Whereas there are many screening methods described for polymer selection based for example on glass forming ability, drug-polymer miscibility, supersaturation, or inhibition of recrystallization, the distinct detection of physico-chemical interactions mostly lacks miniaturized techniques. This work presents an interaction screening assessing the relative viscosity increase between highly concentrated polymer solutions with and without the model drug ketoconazole (KTZ). The fluorescent molecular rotor 9-(2-carboxy-2-cyanovinyl)julolidine was added to the solutions in a miniaturized setup in μL-scale. Due to its environment-sensitive emission behavior, the integrated fluorescence intensity can be used as a viscosity dye within this screening approach (FluViSc). Differences in relative viscosity increases through addition of KTZ were proposed to rank polymers regarding KTZ-polymer interactions. Absolute viscosities were measured with a cone-plate rheometer as a complimentary method and supported the results acquired by the FluViSc. Solid-state nuclear magnetic resonance (ss-NMR) relaxation time measurements and Raman spectroscopy were utilized to investigate drug-polymer interactions at a molecular level. Whereas Raman spectroscopy was not suited to reveal KTZ-polymer interactions, ss-NMR relaxation time measurements differentiated between the selected polymeric carriers hydroxypropylmethylcellulose acetate succinate (HPMCAS) and polyvinylpyrrolidone vinyl acetate 60:40 (PVP-VA64). Interactions were detected for HPMCAS/KTZ ASD while there was no hint for interactions between KTZ and PVP-VA64. These results were in correlation with the FluViSc. The findings were correlated with the dissolution performance of ASD and found to be predictive for supersaturation and inhibition of precipitation during dissolution.

Engineering fast dissolving sodium acetate mediated crystalline solid dispersion of docetaxel

It is hypothesized that a novel crystalline solid dispersion (CSD) of docetaxel (C-DXT) can be engineered by dispersing native docetaxel (DXT, a BCS class II drug) in sodium acetate crystal (SA). DXT is dissolved in glacial acetic/SA solution and freeze-dried. The resulting C-DXT is characterized by differential scanning calorimetry (DSC), powder X-ray analysis (PXRD), LC-MS/MS, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Quartz crystal microbalance with dissipation monitoring (QCM-D) and dynamic light scattering (DLS). Its cytotoxicity on model cancerous (MCF-7, MDA-MB-468) and normal breast cells (MCF-10A) is assessed by MTS assay. SEM/TEM data and the absence of the characteristics peaks of DXT on the DSC curve (at 193.4 °C) and the XRD scan (at 2θ = 15.31 °C and 23.04 °C) confirm the presence of C-DXT in SA. The LC-MS/MS data indicates the chemical stability of DXT. The yield and C-DXT loading are 95.2% and 6.52% w/w, respectively. The C-DXT rapidly forms an aqueous non-rigid nanosuspension with a faster drug dissolution rate compared to native DXT. Unlike, control Tween 80/ethanol, SA is noncytotoxic to normal cells. However, C-DXT's cytotoxicity is time and dose dependent for all diseased cells. This unique CSD process might be applicable to other hydrophobic bioactive agents to enhance their safety and efficacy.