Physicochemical Characterization of Efavirenz–Cyclodextrin Inclusion Complexes

Efavirenz (EFV) is an oral antihuman immunodeficiency virus type 1 drug with extremely poor aqueous solubility. Thus, its gastrointestinal absorption is limited by the dissolution rate of the drug. The objective of this study was to characterize the inclusion complexes of EFV with β-cyclodextrin (β-CD), hydroxypropyl β-CD (HPβCD), and randomly methylated β-CD (RMβCD) to improve the solubility and dissolution of EFV. The inclusion complexation of EFV with cyclodextrins in the liquid state was characterized by phase solubility studies. The solid-state characterization of various EFV and CD systems was performed by X-ray diffraction, differential scanning calorimetry, and scanning electron microscopy analyses. Dissolution studies were carried out in distilled water using US Pharmacopeia dissolution rate testing equipment. Phase solubility studies provided an A_L-type solubility diagram for β-CD and A_P-type solubility diagram for HPβCD and RMβCD. The phase solubility data enabled calculating stability constants (K _s) for EFV-βCD, EFV-HPβCD, and EFV-RMβCD systems which were 288, 469, and 1,073 M⁻¹, respectively. The physical and kneaded mixtures of EFV with CDs generally provided higher dissolution of EFV as expected. The dissolution of EFV was substantially higher with HPβCD and RMβCD inclusion complexes prepared by the freeze drying method. Thus, complexation with HPβCD and RMβCD could possibly improve the dissolution rate-limited absorption of EFV.     

Effect of hydroxypropyl beta cyclodextrin complexation on aqueous solubility,stability, and corneal permeation of acyl ester prodrugs of ganciclovir

The purpose of the study was to investigate the effect of hydroxypropyl beta cyclodextrin (HPβCD) on aqueous solubility, stability, and in vitro corneal permeation of acyl ester prodrugs of ganciclovir (GCV). Aqueous solubility and stability of acyl ester prodrugs of Ganciclovir (GCV) were evaluated in pH 7.4 isotonic phosphate buffer solution (IPBS) in the presence and absence of HPβCD. Butyryl cholinesterase-mediated enzymatic hydrolysis of the GCV prodrugs was studied using various percentage w/v HPβCD. In vitro corneal permeation of GCV and its prodrugs (with and without 5% HPβCD) across isolated rabbit cornea was studied using side-by-side diffusion cells. HPβCD-prodrug complexation was of the A_L type with values for complexation constants ranging between 12 and 108 M⁻¹. Considerable improvement in chemical and enzymatic stability of the GCV prodrugs was observed in the presence of HPβCD. The stabilizing effect of HPβCD was found to depend on the degree of complexation and the degradation rate of prodrug within the complex. Five percent w/v HPβCD was found to enhance the corneal permeation of only the most lipophilic prodrug GCV dibutyrate (2.5-fold compared with 0% HPβCD). All other prodrugs showed little or no difference in transport in the presence of 5% w/v HPβCD. Agitation in the donor chamber largely influenced the transport kinetics of GCV dibutyrate across cornea. Results indicate the presence of an unstirred aqueous diffusion layer at the corneal surface that restricts the transport of the highly lipophilic GCV dibutyrate prodrug. HPβCD improves corneal permeation by solubilizing the hydrophobic prodrug and delivering it across the mucin layer at the corneal surface.     

Characterization of β-lapachone and methylated β-cyclodextrin solid-state systems

The purpose of this research was to explore the utility of β cyclodextrin (βCD) and β cyclodextrin derivatives (hydroxypropyl-β-cyclodextrin [HPβCD], sulfobutylether-β-CD [SB\CD], and a randomly methylated-β-CD [RMβCD]) to form inclusion complexes with the antitumoral drug, β-lapachone (βLAP), in order to overcome the problem of its poor water solubility. RMβCD presented the highest efficiency for βLAP solubilization and was selected to develop solid-state binary systems. Differential scanning calorimetry (DSC), X-ray powder diffractometry (XRPD), Fourier transform infrared (FTIR) and optical and scanning electron microscopy results suggest the formation of inclusion complexes by both freeze-drying and kneading techniques with a dramatic improvement in drug dissolution efficiency at 20-minute dissolution efficiency (DE_20-minute 67.15% and 88.22%, respectively) against the drug (DE_20-minute 27.11%) or the βCD/drug physical mixture (DE_20-minute 27.22%). However, the kneading method gives a highly crystalline material that together with the adequate drug dissolution profile make it the best procedure in obtaining inclusion complexes of RMβCD/βLAP convenient for different applications of βLAP. Published: July 27, 2007     

Cellulose-Based Matrix Microspheres of Prednisolone Inclusion Complex: Preparation and Characterization

The purpose of the present investigation was to encapsulate pure prednisolone (PRD) and PRD–hydroxypropyl-β-cyclodextrin (HPβCD) complex in cellulose-based matrix microspheres. The system simultaneously exploits complexation technique to enhance the solubility of low-solubility drug (pure PRD) and subsequent modulation of drug release from microspheres (MIC) at a predetermined time. The microspheres of various compositions were prepared by an oil-in-oil emulsion–solvent evaporation method. The effect of complexation and presence of cellulose polymers on entrapment efficiency, particle size, and drug release had been investigated. The solid-state characterization was performed by Fourier transform infrared spectroscopy, thermogravimetry, differential scanning calorimetry, and powder X-ray diffractometry. The morphology of MIC was examined by scanning electron microscopy. The in vitro drug release profiles from these microspheres showed the desired biphasic release behavior. After enhancing the solubility of prednisolone by inclusion into HPβCD, the drug release was easily modified in the microsphere formulation. It was also demonstrated that the CDs in these microspheres were able to modulate several properties such as morphology, drug loading, and release properties. The release kinetics of prednisolone from microspheres followed quasi-Fickian and first-order release mechanisms. In addition to this, the f ₂-metric technique was used to check the equivalency of dissolution profiles of the optimized formulation before and after stability studies, and it was found to be similar. A good outcome, matrix microspheres (coded as MIC5) containing PRD–HPβCD complex, showed sustained release of drug (95.81%) over a period of 24 h.     

Preparation and Solid-State Characterization of Inclusion Complexes Formed Between Miconazole and Methyl-β-Cyclodextrin

The aim of this study is to confirm the formation of inclusion complexes between miconazole (MCZ) and two derivatives of beta-cyclodextrin, methyl-beta-cyclodextrin (MβCD) and 2-hydroxypropyl-beta-cyclodextrin (HPβCD) in aqueous solution by phase solubility studies. Inclusion complexes with MβCD in the solid state were then prepared by different methods, i.e., kneading, coevaporation (COE), spray-drying (SD), and lyophilization (LPh). The physicochemical properties of these complexes were subsequently studied by means of differential scanning calorimetry, Fourier transform infrared spectroscopy, scanning electron microscopy, and X-ray diffraction techniques. Phase solubility diagrams with MβCD and HPβCD were classified as A_P type, indicating the formation of 1:1 and 1:2 stoichiometric inclusion complexes. The apparent stability constants (K_S) calculated from the phase solubility diagram were 145.69 M⁻¹ (K _1:1) and 11.11 M⁻¹ (K _1:2) for MβCD and 126.94 M⁻¹ (K _1:1) and 2.20 M⁻¹ (K _1:2) for HPβCD. The method of preparation of the inclusion complexes in the solid state was shown to greatly affect the properties of the formed complex. Hence, the LPh, SD, and COE methods produce true inclusion complexes between MCZ and MβCD. In contrast, crystalline drug was still clearly detectable in the kneaded (KN) product.     

Parenteral Delivery of HPβCD: Effects on Drug-HSA Binding

It is thought that cyclodextrins, such as 2-hydroxypropyl-β-cyclodextrin (HPβCD), will at high concentration affect pharmacokinetics of drugs through competitive binding with plasma proteins. Albumin is the major component of plasma proteins responsible for plasma protein binding. The purpose of this study was to evaluate in vitro the competitive binding of drugs between human serum albumin (HSA) and HPβCD in isotonic pH 7.4 phosphate buffer saline solution (PBS) at ambient temperature. Eight model drugs were selected based on their physicochemical properties and ability to form complexes with HSA and HPβCD. The drug/HPβCD stability constants (K _1:1) were determined by the phase-solubility method and HSA/HPβCD competitive binding determined by an equilibrium dialysis method. Protein binding of drugs that are both strongly protein bound and have high affinity to HPβCD (i.e., have high K _1:1 value) is most likely to be affected by parenterally administered HPβCD. However, this in vitro study indicates that even for those drugs single parenteral dose of HPβCD has to be as high as 70 g to have detectable effect on their protein binding. Weakly protein bound drugs and drugs with low affinity towards HPβCD are insensitive to the cyclodextrin presence regardless their lipophilic properties.     

Influence of hydrophilic polymers on celecoxib complexation with hydroxypropyl β-cyclodextrin

Complexation of celecoxib with hydroxypropyl β-cyclodextrin (HPβCD) in the presence and absence of 3 hydrophilic polymers—polyvinyl pyrrolidone (PVP), hydroxypropyl methylcellulose (HPMC), and polyethylene glycol (PEG)—was investigated with an objective of evaluating the effect of hydrophilic polymers on the complexation and solubilizing efficiencies of HPβCD and on the dissolution rate of celecoxib from the HPβCD complexes. The phase solubility studies indicated the formation of celecoxib-HPβCD inclusion complexes at a 1∶1M ratio in solution in both the presence and the absence of hydrophilic polymers. The complexes formed were quite stable. Addition of hydrophilic polymers markedly enhanced the complexation and solubilizing efficiencies of HPβCD. Solid inclusion complexes of celecoxib-HPβCD were prepared in 1∶1 and 1∶2 ratios by the kneading method, with and without the addition of hydrophilic polymers. The solubility and dissolution rate of celecoxib were significantly improved by complexation with HPβCD. The celecoxib-HPβCD (1∶2) inclusion complex yielded a 36.57-fold increase in the dissolution rate of celecoxib. The addition of hydrophilic polymers also markedly enhanced the dissolution rate of celecoxib from HPβCD complexes: a 72.60-, 61.25-, and 39.15-fold increase was observed with PVP, HPMC, and PEG, respectively. Differential scanning calorimetry and X-ray diffractometry indicated stronger drug amorphization and entrapment in HPβCD because of the combined action of HPβCD and the hydrophilic polymers. Published: September 29, 2006     

Supercritical Extraction of Carotenoids from Rosa canina L. Hips and their Formulation with β-Cyclodextrin

The purpose of this research was to preliminary assess the suitability of a new method for the preparation of a solid formulation in form of powder composed by β-cyclodextrin and the supercritical extract of Rosa canina hips. The method implies the extraction of carotenoids, in particular β-carotene, from freeze dried fruits of R. canina with supercritical CO₂ at 70 °C and 300 bar, in the presence of varying quantity of ethanol as entrainer. The obtained supercritical solution is then expanded at ambient conditions into an aqueous solution of β-cyclodextrin to favour the interaction between β-cyclodextrin and the lipophilic components of the extract. β-carotene solubility (mole fraction) in supercritical CO₂ or in supercritical CO₂/ethanol mixtures were in the order of 1 10⁻⁷. The β-carotene extracted from R. canina fruits (nearly 10 μg/g of dry matrix), interacts almost quantitatively with β-cyclodextrin affording a solid phase, which presents a low apparent solubility in water. Finally the interaction with β-cyclodextrin results in a higher concentration of the β-carotene trans- form relative to the cis- form in the extracted product when collected in an aqueous solution of β-cyclodextrin with respect to the extract in n-hexane.     

Effect of Cyclodextrin Complexation of Curcumin on its Solubility and Antiangiogenic and Anti-inflammatory Activity in Rat Colitis Model

The purpose of the study was to prepare and evaluate the anti-inflammatory activity of cyclodextrin (CD) complex of curcumin for the treatment of inflammatory bowel disease (IBD) in colitis-induced rat model. Inclusion complexes of curcumin were prepared by common solvent and kneading methods. These complexes were further evaluated for increase in solubility of poorly soluble curcumin. The inclusion complexes were characterized for enhancement in solubility, in vitro dissolution, surface morphology, infrared, differential scanning calorimetry, and X-ray studies. Solubility, phase solubility, and in vitro dissolution studies showed that curcumin has higher affinity for hydroxypropyl-β-CD (HPβCD) than other CDs. HPβCD complex of curcumin was further investigated for its antiangiogenic and anti-inflammatory activity using chick embryo and rat colitis model. HPβCD complex of curcumin proved to be a potent angioinhibitory compound, as demonstrated by inhibition of angiogenesis in chorioallantoic membrane assay. Curcumin- and HPβCD-treated rats showed a faster weight gain compared to dextran sulfate solution (DSS) controls. Whole colon length appeared to be significantly longer in HPβCD-treated rats than pure curcumin and DSS controls. An additional finding in the DSS-treated rats was the predominance of eosinophils in the chronic cell infiltrate. Decreased mast cell numbers in the mucosa of the colon of CD of curcumin- and pure-curcumin-treated rats was observed. This study concluded that the degree of colitis caused by administration of DSS was significantly attenuated by CD of curcumin. Being a nontoxic natural dietary product, curcumin could be useful in the therapeutic strategy for IBD patients.     

Quercetin/β-Cyclodextrin Solid Complexes Prepared in Aqueous Solution Followed by Spray-drying or by Physical Mixture

The present study was designed to investigate the influence of operating conditions (temperature, stirring time, and excess amount of quercetin) on the complexation of quercetin with β-cyclodextrin using a 2³ factorial design. The highest aqueous solubility of quercetin was reached under the conditions 37°C/24 h/6 mM of quercetin. The stoichiometric ratio (1:1) and the apparent stability constant (Ks = 230 M⁻¹) of the quercetin/β-cyclodextrin complex were determined using phase-solubility diagrams. The semi-industrial production of a 1:1 quercetin/β-cyclodextrin solid complex was carried out in aqueous solution followed by spray-drying. Although the yield of the spray-drying process was adequate (77%), the solid complex presented low concentration of quercetin (0.14%, w/w) and, thus, low complexation efficiency. The enhancement of aqueous solubility of quercetin using this method was limited to 4.6-fold in the presence of 15 mM of β-cyclodextrin. Subsequently, an inclusion complex was prepared via physical mixture of quercetin with β-cyclodextrin (molar ratio of 1:1 and quercetin concentration of 23% (w/w)) and characterized using infrared spectroscopy, differential scanning calorimetry, nuclear magnetic resonance spectroscopy, and scanning electron microscopy analyses. The enhancement of aqueous solubility of quercetin using this method was 2.2-fold, similar to that found in the complex prepared in aqueous solution before the spray-drying process (2.5-fold at a molar ratio of 1:1, i.e., 6 mM of quercetin and 6 mM of β-cyclodextrin).     

The Role of <Emphasis Type="SmallCaps">l</Emphasis>-arginine in Inclusion Complexes of Omeprazole with Cyclodextrins

In this study, we investigate how the effect of l-arginine (ARG) and cyclodextrins upon omeprazole (OME) stability and solubility. The effect of the presence of ARG on the apparent stability constants (K_1:1) of the inclusion complexes formed between OME and each cyclodextrin, β-cyclodextrin (βCD), and methyl-β-cyclodextrin (MβCD) is studied by phase solubility diagrams and nuclear magnetic resonance (NMR) spectroscopy. The interaction of OME with those cyclodextrins, in the presence of ARG, is characterized using NMR spectroscopy and molecular dynamics simulations. ARG significantly increases the drug solubility and complex stability, in comparison to inclusion complexes formed in its absence. The effect is more pronounced for the OME:βCD complex. ARG also contributes to a larger stability of OME when free in aqueous solution. The combination of ARG with cyclodextrins can represent an important tool to develop stable drug formulations.     

Preformulation Study of the Inclusion Complex Irbesartan-β-Cyclodextrin

The aim of the present work was to improve the solubility and dissolution profile of Irbesartan (IRB), a poorly water-soluble drug by formation of inclusion complex with β-cyclodextrin (βCD). Phase solubility studies revealed increase in solubility of the drug upon cyclodextrin addition, showing A_L—type of graph with slope less than one indicating formation of 1:1 stoichiometry inclusion complex. The stability constant (K _s) was found to be 104.39 M⁻¹. IRB–βCD binary systems were prepared by cogrinding, kneading using alcohol, kneading using aqueous alcohol, and coevaporation methods. Characterization of the binary systems were carried out by differential scanning calorimetry, Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction, and proton nuclear magnetic resonance. The dissolution profiles of inclusion complexes were determined and compared with those of IRB alone and physical mixture. Among the various methods, coevaporation was the best in which the solubility was increased and dissolution rate of the drug was the highest. The study indicated the usefulness of cyclodextrin technology to overcome the solubility problem of IRB.     

Effect of Cyclodextrin Complexation on the Aqueous Solubility and Solubility/Dose Ratio of Praziquantel

Praziquantel (PZQ), the primary drug of choice in the treatment of schistosomiasis, is a highly lipophilic drug that possesses high permeability and low aqueous solubility and is, therefore, classified as a Class II drug according to the Biopharmaceutics Classification System (BCS). In this work, β-cyclodextrin (β-CD) and hydroxypropyl-β-cyclodextrin (HP-β-CD) were used in order to determine whether increasing the aqueous solubility of a drug by complexation with CDs, a BCS-Class II compound like PZQ could behave as BCS-Class I (highly soluble/highly permeable) drug. Phase solubility and the kneading and lyophilization techniques were used for inclusion complex preparation; solubility was determined by UV spectroscopy. The ability of the water soluble polymer polyvinylpyrolidone (PVP) to increase the complexation and solubilization efficiency of β-CD and HP-β-CD for PZQ was examined. Results showed significant improvement of PZQ solubility in the presence of both cyclodextrins but no additional effect in the presence of PVP. The solubility/dose ratios values of PZQ-cyclodextrin complexes calculated considering the low (150 mg) and the high dose (600 mg) of PZQ, used in practice, indicate that PZQ complexation with CDs may result in drug dosage forms that would behave as a BCS-Class I depending on the administered dose.     

Diclofenac-β-cyclodextrin binary systems: Physicochemical characterization and in vitro dissolution and diffusion studies

The aim of this work was to study the influence of β-cyclodextrin (β-CD) on the biopharmaceutic properties of diclofenac (DCF). To this purpose the physicochemical characterization of diclofenac-β-cyclodextrin binary systems was performed both in solution and solid state. Solid phase characterization was performed using differential scanning calorimetry (DSC), powder x-ray diffractometry (XRD), and Fourier transform infrared spectroscopy (FTIR). Phase solubility analyses, and in vitro permeation experiments through a synthetic membrane were performed in solution. Moreover, DCF/β-CD interactions were studied in DMSO by¹H nuclear magnetic resonance (NMR) spectroscopy. The effects of different preparation methods and drug-to-β-CD molar ratios were also evaluated. Phase solubility studies revealed 1∶1 M complexation of DCF when the freeze-drying method was used for the preparation of the binary system. The true inclusion for the freeze-dried binary system was confirmed by¹H NMR spectroscopy, DSC, powder XRD, and IR studies. The dissolution study revealed that the drug dissolution rate was improved by the presence of CDs and the highest and promptest release was obtained with the freeze-dried binary system. Diffusion experiments through a silicone membrane showed that DCF diffusion was higher from the saturated drug solution (control) than the freeze-dried inclusion complexes, prepared using different DCF-β-CD molar ratios. However, the presence of the inclusion complex was able to stabilize the system giving rise to a more regular diffusion profile. Published: October 22, 2005     

Artemether/hydroxypropyl-β-cyclodextrin host–guest system: Characterization, phase-solubility and inclusion mode

An inclusion complex of the antimalarial artemether (ATM) in hydroxypropyl-β-cyclodextrin (HPβCD) was prepared and characterized. The phase-solubility diagram for the drug showed an increase in water solubility and gave an apparent binding constant of 220 M⁻¹. According to ¹H NMR and 2D NMR spectroscopy (ROESY), the inclusion mode involves two CH₃ from the drug orientated in the HPβCD cavity. The complex was characterized by Powder X-ray diffraction and thermal analysis. In addition, the complex produces a 1.81-fold enhancement in apparent bioavailability compared to artemether.     

Danazol-β-cyclodextrin binary system: A potential application in emergency contraception by the oral route

This study explored the potential of β-cyclodextrin to improve the aqueous solubility and dissolution of danazol, investigated a simple and less expensive method for preparation of a danazol-β-cyclodextrin binary system, and explored the potential application of a danazol-β-cyclodextrin binary system as a single-dose emergency contraceptive. Phase solubility analysis indicated formation of a first-order soluble complex with stability constant 972.03 M⁻¹, while Job's plot affirmed 1∶1 stoichiometry. The hyperchromic shift in the UV-Vis spectrum of danazol in the presence of β-cyclodextrin indicated solubilization capability of β-cyclodextrin for danazol. The extrinsic Cotton effect with a negative peak at 280.7 nm confirmed the inclusion of danazol in the asymmetric locus of β-cyclodextrin.¹H-nuclear magnetic resonance analysis suggested that the protons of the steroidal skeleton of danazol display favorable interactions with the β-cyclodextrin cavity. The danazol-β-cyclodextrin binary system was prepared by kneading, solution, freeze-drying, and milling methods. The extent of the enhancement of dissolution rate was found to be dependent on the preparation method. Dissolution studies showed a similar relative dissolution rate (2.85) of the danazol-β-cyclodextrin binary system prepared by the freeze-drying and milling (in the presence of 13% moisture) methods. In a mouse model, the danazol-β-cyclodextrin binary system at 51.2 mg/kg (equivalent to a 400-mg human dose) showed 100% inhibition of implantation when given postcoitally. Moreover, the danazol-β-cyclodextrin binary system is safe up to 2000 mg/kg in the mouse (15.52 g/70 kg human) as a single oral dose. Thus, the danazol-β-cyclodextrin binary system could serve as a new therapeutic application: an oral emergency contraceptive at a physiologically acceptable single dose. Published: May 11, 2007     

A Phase Solubility Study on the Chiral Discrimination of Ibuprofen by ??-Cyclodextrin Complexes

The effects of chiral discrimination in inclusion complexes formed by native β-cyclodextrin and its substituted form (namely methyl-β-cyclodextrin) with racemate or pure enantiomers of the non-steroidal anti-inflammatory drug ibuprofen have been investigated in water. Stability constants and complexation efficiency have been determined for these host–guest systems with a 1:1 molar ratio from phase solubility profiles, showing that in aqueous solution, methylated cyclodextrin is a better complex agent than native cyclodextrin, with more enhanced effects for the (R)-enantiomer. These results have been validated using NMR technique. In particular, ¹H NMR spectra in D₂O show a splitting of the signals for the methyl group and the aromatic protons close to the asymmetric centre of the racemate ibuprofen included in cyclodextrin cavity.     

Antibacterial activity of cyclodextrins against <Emphasis Type="Italic">Bacillus</Emphasis> strains

Growth of alkaliphilic Bacillus halodurans C-125 both on agar plates and in liquid culture was inhibited by methyl-β-cyclodextrin (CD). Furthermore, resting cells of the strain were lysed by contact with methyl-β-CD higher than 10 mM. α-CD also showed lysis activity against Bacillus and related strains. The activity was not observed with Gram-negative and Gram-positive bacteria except for Bacillus strains. Fluorescence staining and scanning electron microscopy of cells revealed that methyl-β-CD disrupted cell membranes, and consequently, the cells were lysed. This is a novel physiological property of CDs.     

Sulfobutyl Ether<Subscript>7</Subscript> β-Cyclodextrin (SBE<Subscript>7</Subscript> β-CD) Carbamazepine Complex: Preparation,Characterization, Molecular Modeling,and Evaluation of <Emphasis Type="Italic">In Vivo</Emphasis> Anti-epileptic Activity

The objective of the present investigation was to study the ability of sulfobutyl ether₇-β-cyclodextrin to form an inclusion complex with carbamazepine, an anti-epileptic drug with poor water solubility. The formation of the complex was carried out using the industrially feasible spray-drying method. The inclusion complex and physical mixtures were characterized by various techniques such as differential scanning calorimetry (DSC), infrared (IR), nuclear magnetic resonance (NMR), X-ray diffraction (XRD), and molecular modeling. The DSC, IR, and NMR studies confirmed the formation of an inclusion complex between carbamazepine and sulfobutyl ether₇ β-cyclodextrin whereas XRD studies indicated an amorphous nature of the inclusion complex. Molecular modeling studies disclosed different modes of interaction between carbamazepine and sulfobutyl ether₇ β-cyclodextrin with good correlation with experimental observations. The inclusion complex exhibited significantly higher in vitro dissolution profile as compared with pure carbamazepine powder. The in vivo anti-epileptic activity of carbamazepine/sulfobutyl ether₇ β-cyclodextrin complex was evaluated in pentylenetetrazole-induced convulsions model. The carbamazepine/sulfobutyl ether₇ β-cyclodextrin complex showed significantly higher anti-epileptic activity (p <0.01) as compared with that of carbamazepine suspension on oral administration.     

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.