Cyclodextrin solubilization of celecoxib: solid and solution state characterization

A recent update of water-soluble polymers in cyclodextrin-based formulations for mucosal drug delivery

Cyclodextrins (CDs) play a crucial role in pharmaceutical formulations due to their unique ability to form inclusion complexes with a wide range of lipophilic drugs. Ternary complexes comprising CD, water-soluble polymer, and drug molecule have emerged as promising multicomponent to the challenges associated with poorly water-soluble drugs. The addition of water-soluble polymer as a ternary component often reduces the amount of CD required to form an inclusion complex thereby decreasing formulation bulk and toxicity. This review outlines the physicochemical properties of CDs and the formation of their inclusion complexes, as well as methods to enhance the complexation efficiency of drug/CD complexes. Additionally, it explores the classification and mucoadhesive properties of water-soluble polymers, and their mechanisms of mucoadhesion on mucosal membranes. The presence of small amounts of water-soluble polymers has been demonstrated to synergistically improve the complexation efficiency of drug/CD complexes. Recent advancements in modified CD-polymer conjugates and the use of water-soluble polymers in CD-based formulations, and their applications across various routes of administration are discussed, highlighting the potential of these ternary complexes as innovative platforms for drug delivery and therapeutic applications.

A look to the future: cyclodextrins and cyclodextrin-based drug delivery to the retina

INTRODUCTION

Retinal diseases are a leading cause of vision loss, affecting millions of people worldwide. Current treatment options are based on invasive methods such as intravitreal injections. Therefore, there is a need for alternative therapeutic strategies that are both effective and more patient-friendly.

AREAS COVERED

Topical drug delivery has gained attention as a preferred noninvasive approach, although it is hindered by several ocular barriers. Cyclodextrin (CD)-based nanoparticles have emerged as a promising strategy to overcome these limitations by enhancing drug permeability in the posterior segment of the eye. This review discusses the potential of CDs as enabling pharmaceutical excipients, their role in improving ocular drug bioavailability, and provides examples of CD-based eye drop formulations currently under development or undergoing clinical trials. Also, the role of CDs as active pharmaceutical agents in ophthalmology is discussed.

EXPERT OPINION

CD-based nanoparticle eye drops present a promising solution and have shown clinical success. CDs are approved pharmaceutical excipients for eye drop formulations and can act as active pharmaceutical ingredients for the treatment of inherent retinal diseases. Future innovations in hybrid CD-based delivery systems and integration of novel therapeutic compounds could provide more efficient and targeted treatment options for retinal diseases.

Formulation and Evaluation of a Silymarin Inclusion Complex-Based Gel for Skin Cancer

Silymarin (SLM) is a bioactive, water-insoluble flavonoid reported against different types of cancer. In the present research, the SLM inclusion complex was prepared by the freeze-drying method using different cyclodextrins. The phase solubility study was performed to assess the stability constant and complexation efficiency. The prepared SLM inclusion complexes (F1, F2, and F3) were characterized for different physicochemical and in vitro parameters. Based on the results, the selected inclusion complex (F2) was converted to a topical gel. Finally, it was evaluated for antioxidant, protein denaturation, and cell viability assay (B16F10; skin cancer cell line). The in vitro results were further confirmed by performing a molecular docking study. The phase solubilization results showed the formation of a stable complex with a stability constant value of 548 mol L-1 (βCD-PLX), 911 mol L-1 (HP βCD-PLX), and 736 mol L-1 (M βCD-PLX). A marked increase in release pattern was found from the prepared inclusion complex (80.9 ± 2.2-97.8 ± 3.1%) compared to free SLM (24.1 ± 2.8%). DSC as well as the IR studies confirm the formation of a stable complex. SEM and X-ray diffraction results confirmed the conversion to the amorphous form. The molecular docking studies exhibited the high docking score of SLM with both colchicine-binding sites of the tubulin protein (-6.28 kcal/mol) and complexing agents, viz., βCD (-4.61 kcal/mol), HP βCD (-5.77 kcal/mol), and M βCD (-5.61 kcal/mol). The antioxidant assay results showed that the activity was significantly improved (1.2-1.6 fold) compared to free SLM. The in vitro cell viability assay outcome displayed concentration-dependent activity with a significantly lower IC50 value from F2G2 (145.3 ± 4.2 μg/mL) than free SLM (304.7 ± 5.7 μg/mL). The above conclusions demonstrated that the developed SLM inclusion complex-based gel system could be an ideal delivery system for skin cancer.

Antimicrobial Preservatives in Cyclodextrin-Containing Drug Formulations

In general, antimicrobial preservatives are essential components of multidose pharmaceutical formulations to prevent microbial growth and contamination, many of which contain lipophilic and poorly water-soluble drugs in need of solubilizing excipients, such as cyclodextrins (CDs). However, CDs frequently reduce or even abolish the antimicrobial activities of commonly used pharmaceutical preservatives. The degree of inactivation depends on the CD complexation of the preservatives, which in turn depends on their chemical structure and physiochemical properties. In general, lipophilic preservatives are more likely to be inactivated; however, CDs are also known to inactivate highly water-soluble preservatives. In some drug formulations, preservative inactivation has been offset by including excipients that possess some antimicrobial activity on their own. In this review, we explain how CDs interact with some commonly used pharmaceutical preservatives and why some preservatives are more susceptible to CD inactivation than others are.

Strategies to Improve the Transdermal Delivery of Poorly Water-Soluble Non-Steroidal Anti-Inflammatory Drugs

The transdermal delivery of non-steroidal anti-inflammatory drugs (NSAIDs) has the potential to overcome some of the major disadvantages relating to oral NSAID usage, such as gastrointestinal adverse events and compliance. However, the poor solubility of many of the newer NSAIDs creates challenges in incorporating the drugs into formulations suitable for application to skin and may limit transdermal permeation, particularly if the goal is therapeutic systemic drug concentrations. This review is an overview of the various strategies used to increase the solubility of poorly soluble NSAIDs and enhance their permeation through skin, such as the modification of the vehicle, the modification of or bypassing the barrier function of the skin, and using advanced nano-sized formulations. Furthermore, the simple yet highly versatile microemulsion system has been found to be a cost-effective and highly successful technology to deliver poorly water-soluble NSAIDs.

Inclusion Complexes of Ethanamizuril with β- and Hydroxypropyl-β-Cyclodextrin in Aqueous Solution and in Solid State: A Comparison Study

Ethanamizuril (EZL) is a new anticoccidial drug developed by our Shanghai Veterinary Research Institute. Since EZL is almost insoluble in water, we conducted a study to improve the solubility of EZL by forming inclusion complexes with β-cyclodextrin (β-CD) and hydroxypropyl-β-cyclodextrin (HP-β-CD). In this study, we performed molecular docking and then systematically compared the interactions of EZL with β-CD and HP-β-CD in both aqueous solution and the solid state, aiming to elucidate the solubilization effect and mechanism of cyclodextrins (CDs). The interactions were also examined in the solid state using DSC, PXRD, and FT-IR. The interactions of EZL with CDs in an aqueous solution were investigated using PSA, UV-vis spectroscopy, MS, 1H NMR, and 2D ROESY. The results of phase solubility experiments revealed that both β-CD and HP-β-CD formed inclusion complexes with EZL in a 1:1 molar ratio. Among them, HP-β-CD exhibited higher Kf (stability constant) and CE (complexation efficiency) values as well as a stronger solubilization effect. Furthermore, the two cyclodextrins were found to interact with EZL in a similar manner. The results of our FT-IR and 2D ROESY experiments are in agreement with the theoretical results derived from molecular simulations. These results indicated that intermolecular hydrogen bonds existing between the C=O group on the triazine ring of EZL and the O-H group of CDs, as well as the hydrophobic interactions between the hydrogen on the benzene ring of EZL and the hydrogen of CDs, played crucial roles in the formation of EZL/CD inclusion complexes. The results of this study can lay the foundation for the future development of high-concentration drinking water delivery formulations for EZL.

Celecoxib/Cyclodextrin Eye Drop Microsuspensions: Evaluation of In Vitro Cytotoxicity and Anti-VEGF Efficacy for Retinal Diseases

Celecoxib (CCB), a cyclooxygenase-2 inhibitor, is capable of reducing oxidative stress and vascular endothelial growth factor (VEGF) expression in retinal cells and has been shown to be effective in the treatment of diabetic retinopathy and age-related macular degeneration. However, the ocular bioavailability of CCB is hampered due to its very low aqueous solubility. In a previous study, we developed 0.5% (w/v) aqueous CCB eye drop microsuspensions (MS) containing randomly methylated β-cyclodextrin (RMβCD) or γ-cyclodextrin (γCD) and hyaluronic acid (HA) as ternary CCB/CD/HA nanoaggregates. Both formulations exhibited good physicochemical properties. Therefore, we further investigated their cytotoxicity and efficacy in a human retina cell line in this study. At a CCB concentration of 1000 μg/mL, both CCB/RMβCD and CCB/γCD eye drop MS showed low hemolysis activity (11.1 ± 0.3% or 4.9 ± 0.2%, respectively). They revealed no signs of causing irritation and were nontoxic to retinal pigment epithelial cells. Moreover, the CCB eye drop MS exhibited significant anti-VEGF activity by reducing VEGF mRNA and protein levels compared to CCB suspended in phosphate buffer saline. The ex vivo transscleral diffusion demonstrated that a high quantity of CCB (112.47 ± 37.27 μg/mL) from CCB/γCD eye drop MS was deposited in the porcine sclera. Our new findings suggest that CCB/CD eye drop MS could be safely delivered to the ocular tissues and demonstrate promising eye drop formulations for retinal disease treatment.

Fabrication of Celecoxib PVP Microparticles Stabilized by Gelucire 48/16 via Electrospraying for Enhanced Anti-Inflammatory Action

Electrospraying (ES) technology is considered an efficient micro/nanoparticle fabrication technique with controlled dimensions and diverse morphology. Gelurice® 48/16 (GLR) has been employed to stabilize the aqueous dispersion of Celecoxib (CXB) for enhancing its solubility and oral bioavailability. Our formula is composed of CXB loaded in polyvinylpyllodine (PVP) stabilized with GLR to formulate microparticles (MPs) (CXB-GLR-PVP MPs). CXB-GLR-PVP MPs display excellent in vitro properties regarding particle size (548 ± 10.23 nm), zeta potential (-20.21 ± 2.45 mV), and drug loading (DL, 1.98 ± 0.059 mg per 10 mg MPs). CXB-GLR-PVP MPs showed a significant (p < 0.05) higher % cumulative release after ten minutes (50.31 ± 4.36) compared to free CXB (10.63 ± 2.89). CXB exhibited good dispersibility, proved by X-ray diffractometry (XRD), adequate compatibility of all components, confirmed by Fourier-Transform Infrared Spectroscopy (FTIR), and spherical geometry as revealed in scanning electron microscopy (SEM). Concerning our anti-inflammatory study, there was a significant decrease in the scores of the inflammatory markers' immunostaining in the CXB-GLR-PVP MPs treated group. Also, the amounts of the oxidative stress biomarkers, as well as mRNA expression of interleukins (IL-1β and IL-6), considerably declined (p < 0.05) in CXB-GLR-PVP MPs treated group alongside an enhancement in the histological features was revealed. CXB-GLR-PVP MPs is an up-and-coming delivery system that could be elucidated in future clinical investigations.

Voriconazole Eye Drops: Enhanced Solubility and Stability through Ternary Voriconazole/Sulfobutyl Ether β-Cyclodextrin/Polyvinyl Alcohol Complexes

Voriconazole (VCZ) is a broad-spectrum antifungal agent used to treat ocular fungal keratitis. However, VCZ has low aqueous solubility and chemical instability in aqueous solutions. This study aimed to develop VCZ eye drop formulations using cyclodextrin (CD) and water-soluble polymers, forming CD complex aggregates to improve the aqueous solubility and chemical stability of VCZ. The VCZ solubility was greatly enhanced using sulfobutyl ether β-cyclodextrin (SBEβCD). The addition of polyvinyl alcohol (PVA) showed a synergistic effect on VCZ/SBEβCD solubilization and a stabilization effect on the VCZ/SBEβCD complex. The formation of binary VCZ/SBEβCD and ternary VCZ/SBEβCD/PVA complexes was confirmed by spectroscopic techniques and in silico studies. The 0.5% w/v VCZ eye drop formulations were developed consisting of 6% w/v SBEβCD and different types and concentrations of PVA. The VCZ/SBEβCD systems containing high-molecular-weight PVA prepared under freeze-thaw conditions (PVA-H hydrogel) provided high mucoadhesion, sustained release, good ex vivo permeability through the porcine cornea and no sign of irritation. Additionally, PVA-H hydrogel was effective against the filamentous fungi tested. The stability study revealed that our VCZ eye drops provide a shelf-life of more than 2.5 years at room temperature, while a shelf-life of only 3.5 months was observed for the extemporaneous Vfend^® eye drops.

Particle Design and Inhalation Delivery of Iodine for Upper Respiratory Tract Infection Therapy

Diseases caused by upper respiratory tract (URT) and pulmonary infections have been a serious threat to human health for millennia and lack of targeted effective therapeutic techniques. In this study, two kinds of cyclodextrin particles with typical particle shapes of nanocubes and microbars were synthesized through a facile process. Subsequently, the particles were used as carriers for loading and stabilizing iodine and characterizations were performed to demonstrate the loading mechanism. Next-generation impactor (NGI) experiments showed that iodine-loaded microbars (I₂@microbars) had a deposition rate of 79.75% in URT, while iodine-loaded nanocubes (I₂@nanocubes) were delivered to the deep lungs with a fine particle fraction (FPF) of 46.30%. Minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) indicated that the iodine-loaded nanocubes and microbars had similar bactericidal effect to povidone iodine solution. Cell viability studies and extracellular pro-inflammatory factor (TNF-α, IL-1β, IL-6) evaluations demonstrate noncytotoxic effects of the blank carriers and anti-inflammatory effects of iodine-loaded samples. The irritation of the rat pharynx by I₂@microbars was evaluated for the behavioral observations, body weight changes, histopathological studies, and TNF-α, IL-1β, and IL-6 levels in pharyngeal tissues. The results showed that I₂@microbars had no irritation to rat pharyngeal tissues at therapeutic doses. In conclusion, the present study provides novel treatment of URT infections via supramolecular cyclodextrin carriers for URT local therapy with iodine loading by a solvent-free method, which enhances the stability and reduces the inherent irritation without inhibiting their antimicrobial effects.

Effect of Soluplus® on γ-cyclodextrin solubilization of irbesartan and candesartan and their nanoaggregates formation

The poor aqueous solubility of irbesartan (IRB) and candesartan cilexetil (CAC) may hamper their bioavailability when orally or topically administered. Among several attempts, the promising nanoaggregate formation by γ-cyclodextrin (γCD) complexation of drugs in aqueous solution with or without water-soluble polymers was investigated. According to phase solubility studies, Soluplus® showed the highest complexation efficiency (CE) of drug/γCD complexes among the polymers tested. The aqueous solubility of IRB and CAC was markedly increased as a function of Soluplus^® concentrations. The binary drug/γCD and ternary drug/γCD/Soluplus^® complex formations were supported and confirmed by solid-state characterizations, including differential scanning calorimetry (DSC), powder X-ray diffraction (PXRD), and Fourier transform infrared (FT-IR) spectroscopy. The true inclusion mode was also proved by proton nuclear magnetic resonance (¹H-NMR) spectroscopy. The nanoaggregate size and morphology of binary and ternary systems were observed using dynamic light scattering (DLS), and transmission electron microscopy (TEM) techniques. The size of these nanocarriers depends on the concentration of Soluplus^®. The use of Soluplus^® could significantly enhance drug solubility and stabilize complex nanoaggregates, which could be a prospective platform for drug delivery systems.

Posterior Segment Ophthalmic Drug Delivery: Role of Muco-Adhesion with a Special Focus on Chitosan

Posterior segment eye diseases (PSEDs) including age macular degeneration (AMD) and diabetic retinopathy (DR) are amongst the major causes of irreversible blindness worldwide. Due to the numerous barriers encountered, highly invasive intravitreal (IVT) injections represent the primary route to deliver drugs to the posterior eye tissues. Thus, the potential of a more patient friendly topical route has been widely investigated. Mucoadhesive formulations can decrease precorneal clearance while prolonging precorneal residence. Thus, they are expected to enhance the chances of adherence to corneal and conjunctival surfaces and as such, enable increased delivery to the posterior eye segment. Among the mucoadhesive polymers available, chitosan is the most widely explored due to its outstanding mucoadhesive characteristics. In this review, the major PSEDs, their treatments, barriers to topical delivery, and routes of topical drug absorption to the posterior eye are presented. To enable the successful design of mucoadhesive ophthalmic drug delivery systems (DDSs), an overview of mucoadhesion, its theory, characterization, and considerations for ocular mucoadhesion is given. Furthermore, chitosan-based DDs that have been explored to promote topical drug delivery to the posterior eye segment are reviewed. Finally, challenges of successful preclinical to clinical translation of these DDSs for posterior eye drug delivery are discussed.

Self-Assembly of Amphiphilic Compounds as a Versatile Tool for Construction of Nanoscale Drug Carriers

This review focuses on synthetic and natural amphiphilic systems prepared from straight-chain and macrocyclic compounds capable of self-assembly with the formation of nanoscale aggregates of different morphology and their application as drug carriers. Since numerous biological species (lipid membrane, bacterial cell wall, mucous membrane, corneal epithelium, biopolymers, e.g., proteins, nucleic acids) bear negatively charged fragments, much attention is paid to cationic carriers providing high affinity for encapsulated drugs to targeted cells. First part of the review is devoted to self-assembling and functional properties of surfactant systems, with special attention focusing on cationic amphiphiles, including those bearing natural or cleavable fragments. Further, lipid formulations, especially liposomes, are discussed in terms of their fabrication and application for intracellular drug delivery. This section highlights several features of these carriers, including noncovalent modification of lipid formulations by cationic surfactants, pH-responsive properties, endosomal escape, etc. Third part of the review deals with nanocarriers based on macrocyclic compounds, with such important characteristics as mucoadhesive properties emphasized. In this section, different combinations of cyclodextrin platform conjugated with polymers is considered as drug delivery systems with synergetic effect that improves solubility, targeting and biocompatibility of formulations.

Formulation of Curcumin-β-cyclodextrin-polyvinylpyrrolidone supramolecular inclusion complex: experimental, molecular docking, and preclinical anti-inflammatory assessment

This research planned to ameliorate an aqueous solubility and dissolution of Curcumin (CUR) by the formulation of inclusion complex with β-cyclodextrin (β-CD) and polyvinylpyrrolidone (PVP). The phase solubility study was performed to assess the solubility of CUR. The prepared CUR complex assessed for dissolution study, physicochemical evaluation, in-vitro antioxidant activity, molecular modeling, and anti-inflammatory assessment. The pivotal findings of phase-solubility studies demonstrate apparent stability constant (Kc) and complexation efficiency (CE) values for CUR-β-CD and CUR-β-CD-PVP complex was 175.4 M ^-1, 1.15% and 833.3.2 M ^-1 and 5.21%, respectively. The characterization results revealed amorphization of crystalline state (CUR) into amorphous state. The maximum drug release found with the ternary CUR complex (F7), i.e. 45.41 ± 3.78% in 6 h study. The chemical shift in the NMR supports that the aromatic ring of CUR is completely complexed inside the β-CD cavity. The antioxidant activity of pure CUR was found to be 58.02 ± 2.21% and CUR ternary complex (F7) showed significantly higher activity to 96.02 ± 2.46%. The in-vivo effect of CUR complex (F7) was also found significantly higher than that of pure CUR. The molecular modeling study depicted that PVP increased the stability of the ternary complex by forming the link between CUR and β-CD. Thus, the ternary inclusion complex of CUR-β-CD-PVP could contribute as an innovative outcome in the enhancement of solubility and in-vivo activity.

Polymeric Nanoparticles for Drug Delivery: Recent Developments and Future Prospects

The complexity of some diseases—as well as the inherent toxicity of certain drugs—has led to an increasing interest in the development and optimization of drug-delivery systems. Polymeric nanoparticles stand out as a key tool to improve drug bioavailability or specific delivery at the site of action. The versatility of polymers makes them potentially ideal for fulfilling the requirements of each particular drug-delivery system. In this review, a summary of the state-of-the-art panorama of polymeric nanoparticles as drug-delivery systems has been conducted, focusing mainly on those applications in which the corresponding disease involves an important morbidity, a considerable reduction in the life quality of patients—or even a high mortality. A revision of the use of polymeric nanoparticles for ocular drug delivery, for cancer diagnosis and treatment, as well as nutraceutical delivery, was carried out, and a short discussion about future prospects of these systems is included.

Computer-Aided Discovery of New Solubility-Enhancing Drug Delivery System

The poor aqueous solubility of active pharmaceutical ingredients (APIs) places a limit on their therapeutic potential. Cyclodextrins (CDs) have been shown to improve the solubility of APIs, but the magnitude of the improvement depends on the structure of both the CDs and APIs. We have developed quantitative structure-property relationship (QSPR) models that predict the stability of the complexes formed by a popular poorly soluble antibiotic, cefuroxime axetil (CA) and different CDs. We applied this model to five CA-CD systems not included in the modeling set. Two out of three systems predicted to have poor stability and poor CA solubility, and both CA-CD systems predicted to have high stability and high CA solubility were confirmed experimentally. One of the CDs that significantly improved CA solubility, methyl-βCD, is described here for the first time, and we propose this CD as a novel promising excipient. Computational approaches and models developed and validated in this study could help accelerate the development of multifunctional CDs-based formulations.

Stimulatory Effects of Soluplus® on Flufenamic Acid β-Cyclodextrin Supramolecular Complex: Physicochemical Characterization and Pre-clinical Anti-inflammatory Assessment

The present study demonstrates the solubility and dissolution of flufenamic acid (FLF)/β-cyclodextrin (β-CD)/Soluplus® supramolecular ternary inclusion complex. The binary and ternary inclusion complexes were prepared using solvent evaporation and the microwave irradiation method. The prepared inclusion complexes were evaluated for physicochemical characterization and anti-inflammatory activity using a murine paw edema mol. The phase solubility studies demonstrated 4.59-fold and 17.54-fold enhancements in FLF solubility with β-CD alone and β-CD:Soluplus® combination compared with pure FLF, respectively. The in vitro drug release results revealed a significant improvement (P < 0.05) in the release pattern compared with pure FLF. Maximum release was found with flufenamic acid binary and ternary complexes prepared using the microwave irradiation method, i.e., 75.23 ± 3.12% and 95.36 ± 3.23% in 60 min, respectively. The physicochemical characterization results showed complex formation and conversion of the crystalline form of FLF to an amorphous form. The SEM study revealed the presence of a more agglomerated and amorphous structure of the solid particles, which confirmed the formation of complexes. The anti-inflammatory effect of the complex was higher than pure FLF. Therefore, the FLF:β-CD:Soluplus® inclusion complex may be a very valuable formulation with improved solubility, dissolution, and anti-inflammatory effect.