Binding specificity between small organic solutes in aqueous solution: classification of some solutes into two groups according to binding tendencies

Complexation of Apigenin and Oxymatrine Leading to Enhanced Anti-inflammatory Activity

Apigenin (APG) is a well-known dietary flavonoid with multiple bioactivities, but its poor aqueous solubility may result in low oral bioavailability and thus compromised therapeutic effects. In the present study, APG was complexed with oxymatrine (OMT), a natural quinolizidine alkaloid, for enhanced anti-inflammatory activity, and the related mechanisms in the interaction of APG with OMT were investigated. Fourier transform-infrared spectroscopy, fluorescence spectroscopy, Raman spectroscopy, and proton nuclear magnetic resonance spectroscopy characterizations demonstrated the occurrence of an APG-OMT complex formed at a molar ratio of 1:2. Then, molecular dynamics simulations and quantum chemical calculations were utilized to elucidate that hydrogen bonding, van der Waals forces, and hydrophobic effects were the main forces acting in the formation of the APG-OMT complex. Pharmacokinetic studies in rats demonstrated that the oral bioavailability of APG in the APG-OMT complex was significantly higher than that of APG alone. Finally, bioactivity evaluation in the lipopolysaccharide-induced acute inflammatory injury mouse models showed that the APG-OMT complex exhibited more potent anti-inflammatory effects than APG alone. This study confirmed that APG and OMT exerted enhanced anti-inflammatory effects through self-complexation, which may provide a novel strategy for improving the bioavailability and bioactivity of natural product mixtures.

Hydroxypropyl-β-cyclodextrin Enhances Oral Absorption of Silymarin Nanoparticles Prepared Using PureNano™ Continuous Crystallizer

The oral bioavailability of drugs is limited by factors such as poor membrane permeability, low solubility, and low dissolution rate. Silymarin (SLM) is a health-food active ingredient that is good for immunosuppression and tumor suppression. However, obtaining a good oral bioavailability is difficult owing to its poor solubility and low dissolution ability. To overcome these concerns, we previously prepared SLM nanoparticles (NPs) using the high-pressure crystallization method (PureNano^TM) and freeze-dried them with erythritol (Ery) or hydroxypropyl-β-CyD (HP-β-CyD) as a water-soluble dispersion stabilizer. In the present study, we investigated the mechanism underlying the improved absorption of SLM/hypromellose (HPMC)/HP-β-CyD NPs after oral administration. The SLM/HPMC nano-suspension prepared using PureNano^TM exhibited a narrow size distribution. The size of the SLM/HPMC/HP-β-CyD NPs was approximately 250 nm after hydration. The SLM/HPMC/HP-β-CyD NPs were rapidly dissolved, and demonstrated a high solubility under supersaturated conditions. Additionally, they exhibited good wettability and their membrane permeability was improved compared with that of SLM original powder. These results suggest that the formulation of SLM NPs using PureNano^TM and freeze-drying with HP-β-CyD improves the absorption of SLM after oral administration by enhancing solubility, wettability, and membrane permeability.

Directly compressed rosuvastatin calcium tablets that offer hydrotropic and micellar solubilization for improved dissolution rate and extent of drug release

The objective was to use caffeine and Soluplus® to improve the dissolution rate and to maintain a concentration of BCS Class II rosuvastatin calcium that exceeds its solubility. Caffeine and Soluplus® together substantially improved the dissolution rate and the extent of rosuvastatin release. Formulations for direct compression tablets included Formulation F1, a control with drug but with neither caffeine nor Soluplus® present; F2 with drug-caffeine complex; F3 with drug and Soluplus® and F4 with drug-caffeine complex and Soluplus®. Each formulation blend provided satisfactory flow properties. Tablets were comparable in mass, hardness and friability. A marked decrease in disintegration time occurred when the hydrotropic or micellar agent was included in the formulation. Assay (98–100%) and content uniformity (99–100%) results met requirements. Release studies in pH 1.2, 6.6, and 6.8 buffers revealed the superiority of F4. At 45 min sampling time, F3 and F4 tablets each provided a cumulative drug release greater than 70% in each medium. F2 tablets exhibited compliance to official standards in pH 6.6 and 6.8 buffers but not in pH 1.2 buffer, whereas tablets based on F1 failed in each medium. Two-factor ANOVA of the release data revealed a statistical difference across the four formulations in each release medium. Pairwise comparison of release profiles demonstrated that, of the four formulations, F4 provided the most effectively enhanced dissolution rate, improvement to the extent of drug release and support of a concentration higher than the solubility of rosuvastatin calcium.

Cyclodextrin-based oral dissolving films formulation of taste-masked meloxicam

This work deals with fast-dissolving drug delivery systems of meloxicam (MX) derived from electrospun polyvinylpyrrolidone (PVP)/2-hydroxypropyl-β-cyclodextrin (HPβCD) nanofiber mats. Electrospinning of solutions with different solvent systems [dimethylformamide (DMF) and ethyl alcohol (EtOH)] was performed. Prepared films were evaluated for morphology, physical, and mechanical properties. MX content, dissolving time, MX release, and cytotoxicity of films were investigated. In vivo studies were also performed in healthy human volunteers. The results showed that MX/HPβCD complexes improved the solubility of MX. PVP also increased MX solubility and the stability of MX/HPβCD complexes. Films were successfully prepared by two solvent systems with fiber in the nanometer range. MX was well incorporated into the films (100% efficiency). The X-ray patterns and DSC experiment indicated an amorphous form of MX. A fast disintegration time and burst release of MX was obtained from EtOH system. Cytotoxicity testing of the films produced by EtOH system proved safer than the DMF system. In vivo studies revealed that films rapidly dissolved in the mouth and had a less bitter taste than MX. These results suggest that electospun films from EtOH system may be a good candidate for fast-dissolving drug delivery systems to increase palatability of dosage forms.

Characterization and In Vitro Evaluation of the Complexes of Posaconazole with β- and 2,6-di-O-methyl-β-cyclodextrin

Posaconazole is a triazole antifungal drug that with extremely poor aqueous solubility. Up to now, this drug can be administered via intravenous injection and oral suspension. However, its oral bioavailability is greatly limited by the dissolution rate of the drug. This study aimed to improve water solubility and dissolution of posaconazole through characterizing the inclusion complexes of posaconazole with β-cyclodextrin (β-CD) and 2,6-di-O-methyl-β-cyclodextrin (DM-β-CD). Phase solubility studies were performed to calculate the stability constants in solution. The results of FT-IR, PXRD, ¹H and ROESY 2D NMR, and DSC all verified the formation of the complexes in solid state. The complexes showed remarkably improved water solubility and dissolution rate than pure posaconazole. Especially, the aqueous solubility of the DM-β-CD complex is nine times higher than that of the β-CD complex. Preliminary in vitro antifungal susceptibility tests showed that the two inclusion complexes maintained high antifungal activities. These results indicated that the DM-β-CD complexes have great potential for application in the delivery of poorly water-soluble antifungal agents, such as posaconazole.

Synthesis and characterization of β-cyclodextrin-conjugated alginate hydrogel for controlled release of hydrocortisone acetate in response to mechanical stimulation

Alginate hydrogels are a class of biomaterials that can be used as local release depots for therapeutic agents. A particular drug that can take advantage of alginate hydrogel for controlled release is hydrocortisone acetate. Hydrocortisone acetate is a widely used anti-inflammatory agent, but is limited in application due to poor solubility and lack of controlled delivery. To overcome this limitation, a mechanically responsive β-cyclodextrin-conjugated alginate (Alg-β-CD) hydrogel was synthesized and characterized for enhanced aqueous solubility and controlled release of hydrocortisone acetate. We demonstrated that mono-6-deoxy-6-ethylenediamine-β-cyclodextrin and hydrocortisone acetate formed a 1:1 inclusion complex, thus resulting in marked increase in hydrocortisone acetate solubility, while causing no significant inhibition to the growth of cultured mouse fibroblasts (L929). More importantly, the release of hydrocortisone acetate from the hydrogel system was increasingly sensitive to mechanical compression, and the mechanical responsiveness of hydrocortisone acetate release increased dramatically as the concentration of mono-6-deoxy-6-ethylenediamine-β-cyclodextrin increased from 0% to 46%, whereas the swelling rate and stiffness of the hydrogel decreased as the concentration of mono-6-deoxy-6-ethylenediamine-β-cyclodextrin increased. The mechanical responsiveness of hydrocortisone acetate release was attributable to conformational distortion of mono-6-deoxy-6-ethylenediamine-β-cyclodextrin moieties and deformation of the polymer network. Moreover, we demonstrated that the hydrogel continuously released and accumulated hydrocortisone acetate in the medium when compressed for up to 72 h, which led to increasing suppression of nitric oxide production in the lipopolysaccharide-stimulated mouse macrophages (RAW264.7), indicating desirable anti-inflammatory effect at the cell level. Hence, this hydrogel system may provide a useful platform for drug delivery, such as hydrocortisone acetate release to wound site, by intentionally generated mechanical force.

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.

Head-To-Head Comparison of Different Solubility-Enabling Formulations of Etoposide and Their Consequent Solubility-Permeability Interplay

The purpose of this study was to conduct a head-to-head comparison of different solubility-enabling formulations, and their consequent solubility-permeability interplay. The low-solubility anticancer drug etoposide was formulated in several strengths of four solubility-enabling formulations: hydroxypropyl-β-cyclodextrin, the cosolvent polyethylene glycol 400 (PEG-400), the surfactant sodium lauryl sulfate, and an amorphous solid dispersion formulation. The ability of these formulations to increase the solubility of etoposide was investigated, followed by permeability studies using the parallel artificial membrane permeability assay (PAMPA) and examination of the consequent solubility-permeability interplay. All formulations significantly increased etoposide's apparent solubility. The cyclodextrin-, surfactant-, and cosolvent-based formulations resulted in a concomitant decreased permeability that could be modeled directly from the proportional increase in the apparent solubility. On the contrary, etoposide permeability remained constant when using the ASD formulation, irrespective of the increased apparent solubility provided by the formulation. In conclusion, supersaturation resulting from the amorphous form overcomes the solubility-permeability tradeoff associated with other formulation techniques. Accounting for the solubility-permeability interplay may allow to develop better solubility-enabling formulations, thereby maximizing the overall absorption of lipophilic orally administered drugs.

Temperature Dependence of the Complexation Mechanism of Celecoxib and Hydroxyl-β-cyclodextrin in Aqueous Solution

Hydroxypropyl-β-cyclodextrin (HP-β-CD) is commonly used as a complexation reagent to solubilize compounds with poor aqueous solubility to improve in vivo dosing. However, the degree of solubility enhancement was often limited by the formation of only a 1:1 complex and a low complexation constant (K). Such a limitation can be significantly improved by the formation of 1:2 complexes in some cases. Despite the understanding of the solubility advantage of the formation of the 1:2 complexes, there is no systematic understanding that could drive for the formation of 1:2 complexes. Thus, in most cases, the formation of 1:2 complexes was limited by observation bases. In this study, we pioneer the usages of molecular dynamics (MD) simulation to understand the phenomena of a model drug of celecoxib (CCB) and HP-β-CD. It has been reported that celecoxib (CCB) forms 1:1 complexes with cyclodextrin in solution; however, some data suggest the existence of a 1:2 complex. The simulation results suggest that a transition state of CCB and HP-β-CD may exit at a higher temperature of CCB and HP-β-CD; a model drug, such as celecoxib (CCB), that is known to form 1:1 complexes can achieve a higher degree of complexation (1:2) and obtain much improved solubility when the same amount of cyclodextrin was used and demonstrated in vitro. The simulation results of CCB and HP-β-CD could be a model system that may provide important insights into the inclusion mechanism.

Formulation and evaluation of meloxicam oral disintegrating tablet with dissolution enhanced by combination of cyclodextrin and ion exchange resins

CONTEXT

The bitter taste of drug is masked by the exchange of ionized drugs with counter ions of ion exchange resin, forming "resinate". Cyclodextrin reduces the unpleasant taste and enhances the drug solubility by encapsulating drug molecules into its central cavity.

OBJECTIVE

Oral disintegrating tablets (ODTs) using the combination of ion exchange resin and cyclodextrin was developed, to mask the bitter taste and enhance drug dissolution.

METHODS

Meloxicam (MX) was selected as a model drug. Formulations containing various forms of MX (free drug, MX-loaded resin or resinate, complexes of MX and 2-hydroxypropyl-β-cyclodextrin (HPβCD) or MX/HPβCD complexes, and a mixture of resinate and MX/HPβCD complexes) were made by direct compression. The ODTs were evaluated for weight variation, thickness, diameter, hardness, friability, disintegration time, wetting time, MX content, MX release, degree of bitter taste and stability.

RESULTS AND DISCUSSION

The tablet hardness was ∼3 kg/in(2), and the friability was <1%. Tablets formulated with resinate and the mixture of resinate and MX/HPβCD complexes disintegrated rapidly within 60 s, which is the acceptable limit for ODTs. These results were corresponded to the in vivo disintegration and wetting times. However, only tablets containing the mixture of resinate and MX/HPβCD complexes provided complete MX dissolution and successfully masked the bitter taste. In addition, this tablet was stable at least 6 months.

CONCLUSIONS

The combination of ion exchange resin and cyclodextrin could be used in ODTs to mask the bitter taste and enhance the dissolution of drugs that are weakly soluble in water.

Fast-acting clotrimazole composited PVP/HPβCD nanofibers for oral candidiasis application

PURPOSE

This study investigates fabrication of clotrimazole (CZ)-composited electrospun Polyvinylpyrrolidone/Hydroxypropyl-β-cyclodextrin (PVP/HPβCD) blended nanofiber mats for oral candidiasis applications.

METHODS

PVP/HPβCD blended nanofiber mats containing clotrimazole were electrospun and characterized using SEM, DSC and XRPD. The solvent system ethanol: water: benzyl alcohol (EtOH:H2O:BzOH) with a 70:20:10 ratio was optimal for the electrospinning process. Various amounts of CZ were loaded into the nanofiber mats. The nanofiber mats was further investigated for drug release, antifungal activity and cytotoxicity.

RESULTS

The fiber diameters in the mats were in the nanometer range. The DSC and XRPD revealed a molecular dispersion of amorphous CZ in the nanofiber mats. The loading capacity increased when CZ content was raised. A fast dissolved and released of CZ from the nanofibers mat was achieved. The ability of the CZ-loaded nanofiber mats to kill the Candida depended on the amount of CZ in the mats; moreover, the CZ-loaded nanofibers killed the Candida significantly faster than the CZ powder and lozenges with low cytotoxicity.

CONCLUSIONS

CZ-loaded nanofiber mats were successfully electrospun. They exhibited rapid antifungal activity in vitro relative to CZ powder and lozenges. Further in vivo studies are needed to investigate for their application in oral candidiasis.

Meloxicam taste-masked oral disintegrating tablet with dissolution enhanced by ion exchange resins and cyclodextrin

The purpose of this study was to develop taste-masked oral disintegrating tablets (ODTs) using the combination of ion exchange resin and cyclodextrin, to mask the bitter taste and enhance drug dissolution. Meloxicam (MX) was selected as a model drug with poor water solubility and a bitter taste. Formulations containing various forms of MX (free drug, MX-loaded resin or resinate, complexes of MX and 2-hydroxypropyl-β-cyclodextrin (HPβCD) or MX/HPβCD complexes, and a mixture of resinate and MX/HPβCD complexes) were made and tablets were prepared by direct compression. The ODTs were evaluated for weight variation, thickness, diameter, hardness, friability, disintegration time, wetting time, MX content, MX release, degree of bitter taste, and stability. The results showed that thickness, diameter, weight, and friability did not differ significantly for all of these formulations. The tablet hardness was approximately 3 kg/in.(2), and the friability was less than 1%. Tablets formulated with resinate and the mixture of resinate and MX/HPβCD complexes disintegrated rapidly within 60 s, which is the acceptable limit for ODTs. These results corresponded to the in vivo disintegration and wetting times. However, only tablets containing the mixture of resinate and MX/HPβCD complexes provided complete MX dissolution and successfully masked the bitter taste of MX. In addition, this tablet was stable at least 6 months. The results from this study suggest that the appropriate combination of ion exchange resin and cyclodextrin could be used in ODTs to mask the bitter taste of drug and enhance the dissolution of drugs that are weakly soluble in water.

Oral delivery of lipophilic drugs: the tradeoff between solubility increase and permeability decrease when using cyclodextrin-based formulations

The purpose of this study was to investigate the impact of oral cyclodextrin-based formulation on both the apparent solubility and intestinal permeability of lipophilic drugs. The apparent solubility of the lipophilic drug dexamethasone was measured in the presence of various HPβCD levels. The drug’s permeability was measured in the absence vs. presence of HPβCD in the rat intestinal perfusion model, and across Caco-2 cell monolayers. The role of the unstirred water layer (UWL) in dexamethasone’s absorption was studied, and a simplified mass-transport analysis was developed to describe the solubility-permeability interplay. The PAMPA permeability of dexamethasone was measured in the presence of various HPβCD levels, and the correlation with the theoretical predictions was evaluated. While the solubility of dexamethasone was greatly enhanced by the presence of HPβCD (K_1∶1 = 2311 M⁻¹), all experimental models showed that the drug’s permeability was significantly reduced following the cyclodextrin complexation. The UWL was found to have no impact on the absorption of dexamethasone. A mass transport analysis was employed to describe the solubility-permeability interplay. The model enabled excellent quantitative prediction of dexamethasone’s permeability as a function of the HPβCD level. This work demonstrates that when using cyclodextrins in solubility-enabling formulations, a tradeoff exists between solubility increase and permeability decrease that must not be overlooked. This tradeoff was found to be independent of the unstirred water layer. The transport model presented here can aid in striking the appropriate solubility-permeability balance in order to achieve optimal overall absorption.

The interaction of nifedipine with selected cyclodextrins and the subsequent solubility-permeability trade-off

The purpose of this study was to investigate the interaction of 2-hydroxypropyl-β-cyclodextrin (HPβCD) and 2,6-dimethyl-β-cyclodextrin (DMβCD) with the lipophilic drug nifedipine and to investigate the subsequent solubility-permeability interplay. Solubility curves of nifedipine with HPβCD and DMβCD in MES buffer were evaluated using phase solubility methods. Then, the apparent permeability of nifedipine was investigated as a function of increasing HPβCD/DMβCD concentration in the hexadecane-based PAMPA model. The interaction with nifedipine was CD dependent; significantly higher stability constant was obtained for DMβCD in comparison with HPβCD. Moreover, nifedipine displays different type of interaction with these CDs; a 1:1 stoichiometric inclusion complex was apparent with HPβCD, while 1:2 stoichiometry was apparent for DMβCD. In all cases, decreased apparent intestinal permeability of nifedipine as a function of increasing CD level and nifedipine apparent solubility was obtained. A quasi-equilibrium mass transport analysis was developed to explain this solubility-permeability interplay; the model enabled excellent quantitative prediction of nifedipine's permeability as a function of CD concentrations. This work demonstrates that when using CDs in solubility-enabling formulations, a trade-off exists between solubility increase and permeability decrease that must not be overlooked. This trade-off was found to be independent of the type of CD-drug interaction. The transport model presented here can aid in striking the appropriate solubility-permeability balance in order to achieve optimal overall absorption.

Characterization of mitotane (o,p'-DDD)--cyclodextrin inclusion complexes: phase-solubility method and NMR

Mitotane (o,p'-dichlorodimethyl dichloroethane [o,p'-DDD]) is used for the treatment of adrenocortical cancer and occasionally Cushing's syndrome. This drug is very poorly soluble in water, and following oral administration, approximately 60% of the dose is recovered in the feces unaltered. The preparation of a soluble formulation (i.e. by complexation with cyclodextrins) with improved bioavailability is the aim of this work. The inclusion of mitotane in methyl-ß-cyclodextrins was studied using both phase-solubility methods and NMR experiments. To elucidate the inclusion mechanism, o,p'-DDD was compared to its regioisomer (i.e. p,p'-DDD). It was demonstrated that two dimethyl-ß-cyclodextrins (DMßCD) can complex with the aromatic rings. From the phase-solubility diagrams, we observe that both cases are very different: K(1:1) is between 37 000 and 85 000 mol.l(-1), whereas K(1:2) is between 5.3 and 32 mol.l(-1). The NMR experiments confirmed the inclusion but it also gave an insight into the kinetics of the dissociation: the ortho-chloro moiety is in slow exchange on the NMR time scale, whereas the para-chloro moiety is in fast exchange rate.

Improvement of drug loading onto ion exchange resin by cyclodextrin inclusion complex

CONTEXT

Ion exchange resins have ability to exchange their counter ions for ionized drug in the surrounding medium, yielding "drug resin complex." Cyclodextrin can be applied for enhancement of drug solubility and stability.

OBJECTIVE

Cyclodextrin inclusion complex of poorly water-soluble NSAIDs, i.e. meloxicam and piroxicam, was characterized and its novel application for improving drug loading onto an anionic exchange resin, i.e. Dowex® 1×2, was investigated.

METHODS

β-Cyclodextrin (β-CD) and hydroxypropyl β-cyclodextrin (HP-β-CD) were used for the preparation of inclusion complex with drugs in solution state at various pH. The inclusion complex was characterized by phase solubility, continuous variation, spectroscopic and electrochemistry methods. Then, the drug with and without cyclodextrin were equilibrated with resin at 1:1 and 1:2 weight ratio of drug and resin.

RESULTS AND DISCUSSION

Solubility of the drugs was found to increase with increasing cyclodextrin concentration and pH. The increased solubility was explained predominantly due to the formation of inclusion complex at low pH and the increased ionization of drug at high pH. According to characterization studies, the inclusion complex was successfully formed with a 1:1 stoichiometry. The presence of cyclodextrin in the loading solution resulted in the improvement of drug loading onto resin.

CONCLUSIONS

Enhancing drug loading onto ion-exchange resin via the formation of cyclodextrin inclusion complex is usable in the development of ion-exchange based drug delivery systems, which will beneficially reduce the use of harmful acidic or basic and organic chemicals.

Studies on the Preparation, Characterization, and Solubility of 2-HP-β-Cyclodextrin-Meclizine HCl Inclusion Complexes

Meclizine HCl is a poorly water-soluble drug having a very slow-onset of action. The effect of 2-hydroxypropyl-β-cyclodextrins and β-cyclodextrins on its aqueous solubility and dissolution rate was investigated. The phase solubility profile indicated that the solubility of Meclizine HCl was significantly increased in the presence of both 2-hydroxypropyl-β-cyclodextrin and β- cyclodextrin; an extend of increase being more for 2-hydroxypropyl-β-cyclodextrin. It was classified as AL-type, indicating the 1:1 stoichiometric inclusion complexes. The complexes formed were quite stable. The solid complexes prepared by physical mixtures, kneading methods, and co-precipitation methods were characterized using differential scanning calorimetry and FTIR. An in vitro study showed that the solubility and dissolution rate of Meclizine HCl were significantly improved by complexation with 2-hydroxypropyl-β-cyclodextrin. Tablet formulation using 1:1 kneading complex of Meclizine HCl and 2-hydroxypropyl-β-cyclodextrin with drug equivalent to 25 mg was prepared by a direct compression method. A dissolution study of prepared tablets was performed in 0.5% SLS in water (pH 7.0). Almost 96% drug was released from the formulation at the end of 30min. A comparison study of prepared tablets was done with marketed a Meclizine HCl 25 mg conventional tablet. From the results of dissolution study, it was found that the prepared formulation was showing better release, which was statistically significant P < 0.01 than a marketed tablet (paired t-test). Only 54% drug release was observed from the marketed tablet at the end of 30 min. Hence this study concludes that the solubility enhancement of Meclizine HCl could be successfully achieved using the inclusion complexation technique.

The Influence of Cyclodextrin and pH on the Solubility of Ketoprofen

Cyclodextrin complexation and pH adjustments have been reported as useful tools to increase the solubility of drug. The aim of this study was to investigate the influence of both cyclodextrin and pH on the overall solubility of ketoprofen. β-cyclodextrin (β-CD) and hydroxypropyl β-cyclodextrin (HP-β-CD) were used for the preparation of inclusion complex by shaking method in aqueous solution at pH 2, 5, 7 and 10. It was found that the solubility of ketoprofen significantly increased with increasing pH and cyclodextrin concentration, showing AL type phase solubility diagram. However, the apparent stability constant of complex (KC) was found to decrease with increasing pH due to the decreased affinity of ionized drug to cyclodextrin cavity. The ionization of ketoprofen increased when the pH was raised, corresponding with its higher zeta potential. The result indicated that the solubility of ketoprofen could be improved by using a combined approach of pH adjustments and complexation with cyclodextrin. Moreover, the unionized drug that was formed by pH adjustments interacted with cyclodextrin more strongly than the ionized drug.

Solubilization of polycyclic aromatics in water by γ-cyclodextrin derivatives

A series of hydrophilic per-6-thio-6-deoxy-γ-cyclodextrins (CDs) were synthesized from per-6-iodo-6-deoxy-γ-CD. These new hosts are able to solubilize polycyclic aromatic guests in aqueous solution to much higher extents than native CDs. Phase-solubility diagrams were mostly linear in accordance with both 1:1 and 1:2 CD-guest complexes in aqueous solution. The stoichiometry of the inclusion complexes was further investigated by fluorescence spectroscopy, which revealed very pronounced Stokes shifts typical for 1:2 complexes. This finding was further consolidated by quantum mechanical calculations of dimer formation of the guests and space-filling considerations by using the cross-sectional areas of the CDs and guests. The calculated dimerization energies correlated well with the binding free energies measured for the 1:2 complexes, and provided the main contribution to the driving force of complexation in the γ-CD cavity.

Potential use of 2-hydroxypropyl-beta-cyclodextrin for preparation of orally disintegrating tablets containing dl-alpha-tocopheryl acetate, an oily drug

To expand the application of a drug in orally disintegrating tablets, the potential use of beta-cyclodextrin (beta-CyD) and 2-hydroxypropyl-beta-cyclodextrin (HP-beta-CyD) as excipients for the tablets containing dl-alpha-tocopheryl acetate (VE), an oily drug, was evaluated. HP-beta-CyD, not beta-CyD, solubilized VE in water through the formation of higher order of complexes at the molar ratio of 1 : 2 (VE : HP-beta-CyD). When prepared under the optimal preparation conditions, the VE tablets containing lactose and 5% (w/w) of HP-beta-CyD, not beta-CyD, had high hardness more than 4 kg and rapid disintegration within 100 s both in vitro and in vivo. In addition, VE tablets containing lactose and 5% (w/w) of HP-beta-CyD, not beta-CyD, maintained the high hardness and rapid disintegration under the accelerated stability test using different conditions for 4 weeks. Therefore, these results suggest the potential use of HP-beta-CyD, not beta-CyD, as an excipient for orally disintegrating tablets containing VE, an oily drug, in the molding method.

Screening for cocrystallization tendency: the role of intermolecular interactions

Pharmaceutical cocrystals have rapidly emerged as a new class of API solids with great promise and advantages. Much work has been focused on exploring the crystal engineering and design strategies that facilitate formation of cocrystals of APIs and ligands/cocrystal formers. However, fewer attempts have been made to understand the equilibrium phase behavior and phase transition kinetics of the cocrystallizing solutions. This limited knowledge on the solution physical chemistry often leads to difficulty in screening for potential molecular pairs of API and ligand that form cocrystals effectively. In this study, the long-time self-diffusivities measured using pulsed gradient spin-echo nuclear magnetic resonance (PGSE NMR) are used to characterize the particle interactions in solutions for pharmaceutical cocrystallizing systems. For the pairs of API and ligand that produce cocrystals, the heteromeric attractions between API and ligand are found to be stronger than the homomeric attractions between API molecules and between ligand molecules, suggesting that an energetically favorable condition is induced for the formation of cocrystals. To the best of our knowledge, this is the first report of using the pair contribution of the self-diffusivity as a screening tool for cocrystal formation.

Cyclodextrins as pharmaceutical solubilizers

Cyclodextrins are useful functional excipients that have enjoyed widespread attention and use. The basis for this popularity from a pharmaceutical standpoint, is the ability of these materials to interact with poorly water-soluble drugs and drug candidates resulting in an increase in their apparent water solubility. The mechanism for this solubilization is rooted in the ability of cyclodextrin to form non-covalent dynamic inclusion complexes in solution. Other solubilizing attribute may include the ability to form non-inclusion based complexes, the formation of aggregates and related domains and the ability of cyclodextrins to form and stabilize supersaturated drug solutions. The increase in solubility also can increase dissolution rate and thus improve the oral bioavailability of BCS Class II and IV materials. A number of cyclodextrin-based products have reached the market based on their ability to camouflage undesirable physicochemical properties. This review is intended to give a general background to the use of cyclodextrin as solubilizers as well as highlight kinetic and thermodynamic tools and parameters useful in the study of drug solubilization by cyclodextrins.

Preparation and evaluation of a Carbopol/HPMC-based in situ gelling ophthalmic system for puerarin

The purpose of this study was to develop a pH-triggered in situ gelling vehicle for ophthalmic delivery of puerarin. The effect of hydroxypropyl-beta-cyclodextrin (HP-beta-CD) on the aqueous solubility and in vitro corneal permeation of puerarin was also investigated. The puerarin solubility increased linearly and proportionally to the HP-beta-CD concentrations and 5% (w/v) HP-beta-CD enhanced its ocular permeability significantly. Carbopol 980NF was used as the gelling agent in combination with HPMC (Methocel E4M) which acted as a viscosity-enhancing agent. The optimum concentrations of Carbopol 980NF and HPMC E4M for the in situ gel-forming delivery systems were 0.1% (w/v) and 0.4% (w/v), respectively. When these two vehicles were combined, an in situ gel that had the appropriate gel strength and gelling capacity under physiological condition could be obtained. This combined solution could flow freely under non- physiological condition and showed the character of pseudoplastic fluid under both conditions. Both in vitro release studies and in vivo pharmacokinetics studies indicated that the combined polymer systems performed better in retaining puerarin than puerarin eye drops did. These results demonstrate that the Carbopol 980NF/HPMC E4M can be a viable alternative to conventional puerarin eye drops to enhance ocular bioavailability and patient compliance.

Stacking complexation by nicotinamide: a useful way of enhancing drug solubility

The solubility enhancement of 11 poorly soluble drugs by complexation using nicotinamide has been studied. The solubilization efficiency of nicotinamide has been compared to that of hydroxypropyl-beta-cyclodextrin and sulfobutylether-beta-cyclodextrin. Solubility enhancements as high as 4000-fold are observed in 20% (w/v) nicotinamide solution. Furthermore, nicotinamide is more effective than cyclodextrins for solubilizing some of the drugs. The mechanism of drug solubilization by nicotinamide is investigated by studying the effects of nicotinamide concentration on the surface tension and the conductivity of water. A slight break in both, the surface tension and conductivity is noticed at around 10% (w/v), suggesting self-association at higher concentrations. Corresponding breaks in the solubility profiles of estrone and griseofulvin at similar concentrations support self-association. Based on this observation it appears that at low concentrations, one molecule of nicotinamide undergoes complexation with one drug molecule to form a 1:1 complex. At higher concentrations, two molecules of nicotinamide undergo complexation with one drug molecule forming a 1:2 complex. The complexation constants have been calculated for all the drugs and the data are well described by this model. Expectedly, increasing the temperature reduces the complexation constants.

Improvement of Solubility and Oral Bioavailability of 2-(N-Cyanoimino)-5-{(E)-4-styrylbenzylidene}-4-oxothiazolidine (FPFS-410) with Antidiabetic and Lipid-Lowering Activities in Dogs by 2-Hydroxypropyl-.BETA.-cyclodextrin

2-(N-Cyanoimino)-5-[(E)-4-styrylbenzylidene]-4-oxothiazolidine (FPFS-410) is a newly synthesized thiazolidine derivative having not only antidiabetic but also lipid-lowering activities. However, this compound has an extremely low aqueous solubility (2.8 (+/-0.33) x 10(-8) M (0.0094+/-0.0011 microg/ml) in 1.0 M phosphate buffer (pH 7.0) at 25 degrees C). In this study, we investigated the effect of various hydrophilic cyclodextrins (CyDs) on the solubility of FPFS-410 to select a CyD suitable for formulations of the compound. Among various CyDs, 2-hydroxypropyl-beta-CyD (HP-beta-CyD) had the highest solubilizing ability to FPFS-410, e.g., the solubility of the compound was increased 200000-fold by the addition of 40 mM HP-beta-CyD, which was attributable to the formation of the 1 : 2 (guest : host) inclusion complexes. The interaction of HP-beta-CyD with FPFS-410 was studied using 1H-nuclear magnetic resonance (NMR) spectroscopies including ROESY spectroscopy and a molecular modeling calculation. These results suggested that HP-beta-CyD forms a 1:2 (guest : host) inclusion complex with FPFS-410 by including both the stilbene and thiazolidine moieties. FPFS-410/HP-beta-CyD solid complexes with various stoichiometries were prepared by the spray drying and cogrinding methods, and confirmed by powder X-ray diffractometry that these complexes are in an amorphous state. The dissolution of FPFS-410 in water was significantly accelerated by the complexation with HP-beta-CyD. In vivo studies revealed that HP-beta-CyD markedly increases the bioavailability of FPFS-410 after oral administration in dogs. The present results suggest that HP-beta-CyD is useful for improvement of the extremely low bioavailability of FPFS-410.

Formulation and biological evaluation of glimepiride-cyclodextrin-polymer systems

Glimepiride is one of the third generation sulfonylureas used for treatment of type 2 diabetes. Poor aqueous solubility and slow dissolution rate of the drug lead to irreproducible clinical response or therapeutic failure in some cases due to subtherapeutic plasma drug levels. Consequently, the rationale of this study was to improve the biological performance of this drug through enhancing its solubility and dissolution rate. Inclusion complexes of glimepiride in beta-cyclodextrin (beta-CyD), hydroxypropyl-beta-cyclodextrin (HP-beta-CyD) and sulfobutylether-beta-cyclodextrin (SBE-beta-CyD), with or without water soluble polymers were prepared by the kneading method. Binary systems were characterized by thermogravimetric analysis, IR spectroscopy and X-ray diffractometry. Phase solubility diagrams revealed increase in solubility of the drug upon cyclodextrin addition, showing A(p) type plot indicating high order complexation. All the ternary systems containing beta-CyD or HP-beta-CyD showed higher dissolution efficiency compared to the corresponding binary systems. The hypoglycemic effect of the most rapidly dissolving ternary system of glimepiride-HP-beta-CyD-PEG 4000 was evaluated after oral administration in diabetic rats by measuring blood glucose levels. The results indicated that this ternary system improves significantly the therapeutic efficacy of the drug. In conclusion, the association of water soluble polymers with glimepiride-CyD systems leads to great enhancement in dissolution rate, increased duration of action and improvement of therapeutic efficacy of the drug.

An ocular drug delivery system containing zinc diethyldithiocarbamate and HPbetaCD inclusion complex--corneal permeability, anti-cataract effects and mechanism studies

Our purpose was to study the formulation and anti-cataract effects of aqueous eye drops containing a high concentration of zinc diethyldithiocarbamate (Zn-DDC). A possible mechanism of the anti-cataract effect of Zn-DDC was also studied. Zn-DDC and hydroxypropyl-beta-cyclodextrin (HPbetaCD) inclusion complex (Zn-DDC/HPbetaCD) was studied using the saturation solution method and characterized by differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (IR). Suitable formulations for Zn-DDC eye drops were established by means of in-vitro trans-corneal penetration experiments. The anti-cataract effect of the selected formulation was demonstrated by the delay in lens opacity development in hereditary shumuya cataract rats (SCRs). Semiquantitative reverse transcription polymerase chain reaction (RT-PCR) was performed to study the effect of diethyldithiocarbamate (DDC), a metabolite of Zn-DDC, on the transcription inducible nitric oxide synthase (iNOS) mRNA in human lens epithelial cells (HLEC). In the presence of 22% (w/v) HPbetaCD, the solubility of Zn-DDC in water (0.2 mM) was increased almost 850 fold (to 17 mM), by the formation of Zn-DDC/HPbetaCD. The stoichiometry of Zn-DDC inclusion was 1:1. The Zn-DDC/HPbetaCD stability constant, Ks (1:1) was estimated to be 3453 M(-1). The ophthalmic preparation containing 0.1% HPMC and 0.1% poloxamer 188 (P188) exhibited better permeability than the others in-vitro, and significantly delayed cataract formation in SCRs compared with non-treated SCRs. DDC inhibits the transcription of iNOS mRNA in HLEC. We concluded that this drug delivery system increases both the drug solubility in aqueous eye drops and the permeability of drug through the rabbit cornea, by the formation of a drug-cyclodextrin inclusion complex and the addition of polymers and penetration enhancers. The preparation effectively prevented the development of cataracts in SCRs. DDC, the metabolite of Zn-DDC, may be one of the factors in the prevention of cataract formation because it inhibits the transcription of iNOS mRNA.

Bioavailability and anticataract effects of a topical ocular drug delivery system containing disulfiram and hydroxypropyl-beta-cyclodextrin on selenite-treated rats

PURPOSE

To test the effect of aqueous eye drops containing a high concentration of disulfiram (DSF) in a cyclodextrin- based drug delivery system. This system increases both the drug solubility in aqueous eye drops and the permeability of drug into the rabbit eye, by the formation of a drug-cyclodextrin inclusion complex, and so enhances the ocular bioavailability and anti-cataract effect of DSF.

METHODS

The DSF and hydroxypropyl-beta-cyclodextrin (HPbetaCD) inclusion (DSF/HPbetaCD) was studied using solubility methods, IR spectra and X-ray diffraction patterns. Suitable formulations for DSF eye drops were first identified by a trans-corneal penetration experiment in vitro. Finding a new p-bromophenacyl bromide (p-BPB) derivative reagent for diethyldithiocarbamic acid (DDC), which was a metabolite of DSF, allowed precise determination of the contents of DSF in aqueous humor. The ocular bioavailability was calculated by a transcorneal experiment of DSF in vivo. The lens opacity of a selenite-induced cataract in rat pups was monitored using a slit lamp with an anterior eye segment analysis system.

RESULTS

The formation of DSF/HPbetaCD inclusion and the addition of hydroxypropylmethylcellulose (HPMC), as a penetration enhancer, played very important roles in increasing the ocular bioavailability of DSF. DSF eye drops, with a formulation of 1.26% (w/v) DSF/HPbetaCD inclusion, 0.01% (w/v) HPMC, 0.005% (w/v) benzalkonium chloride and 0.9% (w/v) sodium chloride, inhibited the onset of selenite-induced cataracts effectively.

CONCLUSIONS

The cyclodextrin-based drug delivery system enhances both the solubility of DSF in aqueous eye drops and permeability of the drug into the rabbit eye. DSF ocular bioavailability in rabbit aqueous humor exceeded those reported for the DSF ophthalmic preparation. DSF eye drops effectively prevent the development of selenite-induced cataracts.

Delivery of all trans-retinoic acid (RA) to hepatocyte cell line from RA/galactosyl α-cyclodextrin inclusion complex

All trans-retinoic acid (RA) plays a role in regulation of P450RAI gene expression. In this study, hepatocyte cell line (HepG2) was used to study an effect of RA released from RA/galactosyl alpha-cyclodextrin (GCD) inclusion complex on regulation of P450RAI gene expression. A delivery system composed of RA/GCD inclusion complex was applied because RA is poorly water soluble, and organic solvents used to dissolve it often interfere with cytotoxicity. Solubility of RA in water was increased by forming complex with GCD. Inclusion complex between GCD and RA was checked by (1)H-nuclear magnetic resonance, Fourier transformation infrared (FT-IR) spectroscopy and X-ray diffraction (XRD). The chemical shifts of the interior and exterior GCD protons in the presence of RA indicated that the RA was included within the GCD macrocycle cavity. The carbonyl band of RA and crystalline peak of RA in RA/GCD inclusion complex disappeared from FT-IR and XRD measurements, respectively, indication of inclusion complex between RA and GCD. From the observation of fluorescence micrograph of hepatocytes and flow cytometry measurement of HepG2, the internalization of fluorescein isothiocyanate-GCD by the hepatocyte occurred. Gene expression of P450RAI in HepG2 by delivery of RA from RA/GCD complex was observed.

Influence of cyclodextrins on in vitro human skin absorption of the sunscreen, butyl-methoxydibenzoylmethane

The effects of hydroxypropyl-beta-cyclodextrin (HP-beta-CD) and sulfobutylether-beta-CD (SBE7-beta-CD) on in vitro human skin penetration and retention of the sunscreen agent butyl-methoxydibenzoylmethane (BM-DBM) were investigated. The interaction between the UV filter and the cyclodextrins was studied in water by phase-solubility analysis. Solid complexes were prepared by the co-evaporation method and characterized by (1)H NMR spectroscopy, thermal analysis and powder X-ray diffraction. Solutions containing BM-DBM free or complexed with cyclodextrins were applied to excised human skin in Franz diffusion cells and the amount of sunscreen permeated after 6 h into the stratum corneum, viable epidermis, dermis and receptor fluid was assessed by HPLC. As much as 14.10-16.78% of the applied dose of BM-DBM penetrated within the skin tissue. No sunscreen was detected in the dermis and in the receiver phase. The greater proportion (84.6-95.5%) of the absorbed UV filter was localized in the stratum corneum with no significant differences between uncomplexed or complexed BM-DBM. Notable levels (2.29% of the applied dose) of the sunscreen agent accumulated in the epidermis from the preparation containing free BM-DBM. The epidermal concentration of the UV filter was markedly reduced (0.66% of the applied dose) by complexation with SBE7-beta-CD, whereas HP-beta-CD had no effect. The decreased BM-DBM retention in the epidermal region achieved by SBE7-beta-CD limits direct contact of the sunscreen and of its reactive photolytic products with the skin viable tissues.