The effect of mechanical grinding on the formation, crystalline changes and dissolution behaviour of the inclusion complex of telmisartan and β-cyclodextrins

Application of Biomaterials in the Development of Hydrogel-Forming Microneedles Integrated with a Cyclodextrin Drug Reservoir for Improved Pharmacokinetic Profiles of Telmisartan

Telmisartan (TEL) is a promising antihypertensive agent among other angiotensin receptor blockers. However, its oral application is limited by its poor water solubility. This study presents the successful utilization of biomaterial-based hydrogel-forming microneedles integrated with a direct compressed tablet reservoir (HFMN-DCT) for the transdermal delivery of telmisartan in the treatment of hypertension. The combination of PVP, PVA, and tartaric acid was used in the HFMN formulation. A range of cross-linking temperatures and times were employed to optimize the characteristics of the HFMN. The HFMN exhibited excellent swelling capacity, mechanical strength, and insertion properties. Additionally, the poorly soluble characteristic of TEL was improved by the inclusion complex formulation with β-cyclodextrin (βCD). Phase solubility analysis showed an Ap-type diagram, indicating a higher-order complex between TEL and βCD, with respect to βCD. A ratio of TEL:βCD of 1:4 mM demonstrates the highest solubility enhancement of TEL. The inclusion complex formation was confirmed by FTIR, XRD, DSC, and molecular docking studies. A significantly higher release of TEL (up to 20-fold) from the inclusion complex was observed in the in vitro release study. Subsequently, a DCT reservoir was developed using various concentrations of sodium starch glycolate. Essentially, both the HFMN and DCT reservoir exhibit hemocompatibility and did not induce any skin irritation. The optimized combination of the HFMN-DCT reservoir showed an ex vivo permeation profile of 83.275 ± 2.405%. Notably, the proposed system showed superior pharmacokinetic profiles in the in vivo investigation using male Wistar rats. Overall, this study highlights the potential of HFMN-DCT reservoir systems as a versatile platform for transdermal drug delivery applications.

The dissolution of p-methoxycinnamic acid-β-cyclodextrin inclusion complex produced with microwave irradiation

Background: p-methoxycinnamic acid (pMCA) is an ethyl p-methoxycinnamic derivative, which is the largest active ingredient in the rhizome of the kencur (Kaempferia galanga L) plant. Several studies reported that the compound has anti-inflammatory activity but has low solubility in water. The formation of a pMCA-β-cyclodextrin (βCD) inclusion complex with a molar ratio of 1:1 can increase its solubility. The formation of inclusion complexes with conventional methods requires a long time and the yield value is not optimal. Objective: This study aims to evaluate the dissolution of the pMCA-βCD inclusion complex produced using the microwave irradiation method. Methods: The product was manufactured with chloroform solvent and a power of 400 watts (power 80%). It was then evaluated using the Differential Thermal Analysis (DTA) every 2 minutes until the 8th minute. The reaction was complete after 4 minutes of treatment with a yield of 96.5%. The obtained inclusion complexes were evaluated using DTA, FTIR, and PXRD. Subsequently, a dissolution test was carried out using a type 2 apparatus in distilled water medium of pH 6.8±0.05 at 37±0.5°C. Results: The results showed that there was a change in the melting temperature profile, infrared spectra, and crystallinity of the product. An 89.18% dissolution was also obtained within 60 minutes, which was twice that of pMCA compounds. Conclusion: From the results of the study, it can be concluded that the formation of pMCA-βCD inclusion complexes using the microwave irradiation method is capable of providing high-yield values in a short time.

A new Febuxostat-Telmisartan Drug-Drug Cocrystal for Gout-Hypertension Combination Therapy

Drug-drug cocrystalllization is a novel mechanism for effective pharmacological combination therapy. In this work, we have demonstrated the preparation of a drug-drug cocrystal of a hypertension drug (Telmisartan; TEL) with a hyperuricemia drug (Febuxostat; FEB) in 1:1 molar ratio using a solvent evaporation method for the first time. Generally, a multi-component system may yield either a eutectic, salt, and/or a cocrystal. This study adopted a methodical orthogonal framework to analyze the final solid form. A single crystal X-ray structural investigation revealed the formation of a heterosynthon with carboxylic and benzimidazole groups of FEB and TEL, respectively, in the triclinic P-1 space group. ΔpKa of the heterosynthon is ∼1.5, hence, based on the empirical rules, a salt-cocrystal continuum is hypothesized. Further, attenuated total reflectance Fourier transform infrared (ATR-FTIR), and Raman spectroscopy were employed to corroborate the hydrogen bond formation in the heterosynthon (-N---H-O-), which confirmed the propensity for cocrystal formation. An accelerated stability study and an in vitro biorelevant dissolution study of the cocrystal were performed, which demonstrated that it is physiochemically stable, but it resulted in a slower dissolution rate when compared with plain drugs.

Cyclodextrin Inclusion Complexes and Their Application in Food Safety Analysis: Recent Developments and Future Prospects

Food safety issues are a major threat to public health and have attracted much attention. Therefore, exploring accurate, efficient, sensitive, and economical detection methods is necessary to ensure consumers' health. In this regard, cyclodextrins (CDs) are promising candidates because they are nontoxic and noncaloric. The main body of CDs is a ring structure with hydrophobic cavity and hydrophilic exterior wall. Due to the above characteristics, CDs can encapsulate small guest molecules into their cavities, enhance their stability, avoid agglomeration and oxidation, and, at the same time, interact through hydrogen bonding and electrostatic interactions. Additionally, they can selectively capture the target molecules to be detected and improve the sensitivity of food detection. This review highlights recent advances in CD inclusion technology in food safety analysis, covering various applications from small molecule and heavy metal sensing to amino acid and microbial sensing. Finally, challenges and prospects for CDs and their derivatives are presented. The current review can provide a reference and guidance for current research on CDs in the food industry and may inspire breakthroughs in this field.

Identification of Photocatalytic Alkaloids from Coptidis Rhizome by an Offline HPLC/CC/SCD Approach

Natural products continue to be a valuable source of active metabolites; however, researchers of natural products are mostly focused on the biological effects, and their chemical utility has been less explored. Furthermore, low throughput is a bottleneck for classical natural product research. In this work, a new offline HPLC/CC/SCD (high performance liquid chromatography followed by co-crystallization and single crystal diffraction) workflow was developed that greatly expedites the discovery of active compounds from crude natural product extracts. The photoactive total alkaloids of the herbal medicine Coptidis rhizome were firstly separated by HPLC, and the individual peaks were collected. A suitable coformer was screened by adding it to the individual peak solution and observing the precipitation, which was then redissolved and used for co-crystallization. Seven new co-crystals were obtained, and all the single crystals were subjected to X-ray diffraction analysis. The molecular structures of seven alkaloids from milligrams of crude extract were resolved within three days. NDS greatly decreases the required crystallization amounts of alkaloids to the nanoscale and enables rapid stoichiometric inclusion of all the major alkaloids with full occupancy, typically without disorder, affording well-refined structures. It is noteworthy that anomalous scattering by the coformer sulfur atoms enables reliable assignment of absolute configuration of stereogenic centers. Moreover, the identified alkaloids were firstly found to be photocatalysts for the green synthesis of benzimidazoles. This study demonstrates a new and green phytochemical workflow that can greatly accelerate natural product discovery from complex samples.

New and developing pharmacotherapies for hypertension

INTRODUCTION

Despite the significant contribution of hypertension to the global burden of disease, disease control remains poor worldwide. Considering this unmet clinical need, several new antihypertensive drugs with novel mechanisms of action are under development.

AREAS COVERED

The present review summarizes the recent advances in the development of emerging pharmacological agents for the management of hypertension. The latest technological innovations in the design of optimized formulations of available antihypertensive drugs and the potential role of the modification of intestinal microbiota to improve blood pressure (BP) control are also covered.

EXPERT OPINION

Significant efforts have been made to develop new antihypertensive agents with novel actions that target the main mechanisms involved in resistant hypertension. Sacubitril/valsartan may emerge as a potential first-line drug due to its superiority over renin angiotensin system inhibitors, and SGLT2 inhibitors can reduce BP in difficult-to-control hypertensive patients with type 2 diabetes. In addition, firibastat and aprocitentan may expand the therapeutic options for resistant hypertension by novel mechanism of actions. Since gut dysbiosis not only leads to hypertension but also causes direct target organ damage, prebiotics and probiotics could represent a potential strategy to prevent or reduce the development of hypertension and to contribute to BP control.

PTSA-catalyzed selective synthesis and antibacterial evaluation of 1,2-disubstituted benzimidazoles

Herein, we developed a convenient and efficient method via protonation of p-toluenesulfonic acid promoted cyclocondensation of o-phenylenediamine and aldehydes for selectively synthesizing 1,2-disubstituted benzimidazoles. This method displayed broad substrate adaptability and afforded the desired products in moderate to excellent yield in short reaction time. The effect of different substituents on the yield was investigated by extending optimum reaction conditions, which was further confirmed by theoretical calculations. It suggested that the surface electrostatic potential of oxygen atom and nitrogen atom on the substrates played important role in the synthesis of 1,2-disubstituted benzimidazoles. Besides, the crystal structure of compound 2t in the orthorhombic space group P2(1)/c was presented. Also, the anti-mycolicibacterium smegmatis (MC2155) activity was evaluated using rifampicin as a positive control. The products (2a, 2b, 2c, 2i, 2j, 2k, 2m) showed good antibacterial activities which were comparable to rifampicin.

Cyclodextrins inclusion complex: Preparation methods, analytical techniques and food industry applications

This review offers a vision of the chemical behaviour of natural ingredients, synthetic drugs and other related compounds complexed using cyclodextrins. The review takes care of different sections related to i) the inclusion complexes formation with cyclodextrins, ii) the determination of the inclusion formation constant, iii) the most used methods to prepare host inclusion in the non-polar cavity of cyclodextrins and iv) the analytical techniques to evidence host inclusion. The review provides different literature that shows the application of cyclodextrins to improve physical, chemical, and biological characteristics of food compounds including solubility, stability and their elimination/masking. Moreover, the review also offers examples of commercial food/supplement products of cyclodextrins to indicate that cyclodextrins can be used to generate biotechnological substances with innovative properties and improve the development of food products.

The effect of drug loading on the properties of abiraterone-hydroxypropyl beta cyclodextrin solid dispersions processed by solvent free KinetiSol® technology

Abiraterone is a poorly water-soluble drug used in the treatment of prostate cancer. In our previous study, we reported that KinetiSol® processed solid dispersions (KSDs) based on hydroxypropyl β-cyclodextrin (HPBCD) showed improved dissolution and pharmacokinetics of abiraterone. However, the nature of abiraterone-HPBCD interaction within the KSDs or the effect of drug loading on the physicochemical properties and in vivo performance of HPBCD-based KSDs remain largely unknown. We hypothesize that KinetiSol technology can prepare abiraterone-HPBCD complexes within KSDs and that increasing the drug loading beyond an optimal point reduces the in vitro and in vivo performance of these KSDs. To confirm our hypothesis, we developed KSDs with 10-50% w/w drug loading and analyzed them using X-ray diffractometry and modulated differential scanning calorimetry. We found that KSDs containing 10-30% drug were amorphous. Interestingly, two-dimensional solid-state nuclear magnetic resonance and Raman spectroscopy indicated that the abiraterone-HPBCD complexes were formed. At elevated temperatures, the 10% and 20% drug-loaded KSDs were physically stable, while the 30% drug-loaded KSD showed recrystallization of abiraterone. In vitro dissolution and in vivo pharmacokinetic performances improved as the drug loading decreased; we attribute this to increased noncovalent interactions between abiraterone and HPBCD at lower drug loadings. Overall, the 10% drug loaded KSD showed a dissolution enhancement of 15.7-fold compared to crystalline abiraterone, and bioavailability enhancement of 3.9-fold compared to the commercial abiraterone acetate tablet Zytiga®. This study is first to confirm that KinetiSol, a high-energy, solvent-free technology, is capable of forming abiraterone-HPBCD complexes. Furthermore, in terms of in vitro and in vivo performance, a 10% drug load is optimal.

Preparation and Evaluation of Co-amorphous Formulations of Telmisartan-Amino Acids as a Potential Method for Solubility and Dissolution Enhancement

Telmisartan (TLM) is a potent antihypertensive drug with pH-dependent aqueous solubility. This work aimed to enhance the solubility and dissolution rate of TLM by the co-amorphous drug amino acid (AA) approach by combining TLM, with different types and ratios of AAs. The co-amorphous TLM-AA blends were prepared by freeze-drying and investigated for solid-state characteristics like the dissolution rate enhancement of TLM. Among the prepared co-amorphous formulations, TLM-arginine (ARG) exhibited the greatest enhancement in solubility with increasing the molar ratio of ARG. The TLM-ARG at 1:2 ratio showed about a 57-fold increase in solubility of TLM and the highest dissolution percentage in phosphate buffer (pH7.5) (100% in 20 minutes) compared to both crystalline TLM (20% in 60 min) and physical mixture. Powder XRD, DSC, FTIR analysis and SEM demonstrated the formation of amorphous form within the co-amorphous formulations. Only TLM:ARG (1:0.5) were stable at (40°C, 75% RH) for a minimum of 90 days. In conclusion, ARG was able to stabilize the amorphous form of TLM and enhances its aqueous solubility and dissolution. The 1:2 w/w ratio of TLM-ARG co-amorphous showed the best solubility and dissolution rate while the 1:0.5 w/w ratio showed the best stability.

Supramolecular polyelectrolyte complexes based on cyclodextrin-grafted chitosan and carrageenan for controlled drug release

In the present study, supramolecular polyelectrolyte complexes (SPEC) based on a cyclodextrin-grafted chitosan derivative and carrageenan were prepared and evaluated for controlled drug release. Samples were characterized by FTIR, SEM, and ζ-potential measurements, which confirmed the formation of the polymeric complex. The phenolphthalein test confirmed the presence and availability of inclusion sites from the attached βCD. Silver sulfadiazine was used as the model drug and the association with the SPEC was studied by FTIR and computational molecular modeling, using a semi-empirical method. DRS and TEM analyses have shown that Ag⁺ ions from the drug were reduced to form metallic silver nanostructures. In vitro tests have shown a clear bacterial activity toward Gram-positive bacteria Staphylococcus aureus and Enterococcus durans/hirae and Gram-negative bacteria Klebsiella pneumoniae and Escherichia coli. Finally, this work shows that βCD-chitosan/carrageenan supramolecular polyelectrolyte complexes hold an expressive potential to be applied as a polymer-based system for controlled drug release.

Supramolecular Interactions between β-Cyclodextrin and the Nucleobase Derivatives of Ferrocene

Novel conjugates of ferrocene with uracil, 5-fluorouracil, tegafur, or acyclovir are reported. Their synthesis involved (i) the azide-alkyne 1,3-dipolar cycloaddition or (ii) the formation of the ester linkage. For the first time, we present an in-depth insight into the supramolecular interactions between β-cyclodextrin and ferrocene-nucleobase derivatives. Spectroscopic and voltammetric analyses performed within this work suggested that the ferrocene or adamantane unit of the conjugates interacted with the β-cyclodextrin's inner cavity. The methods applied for the supramolecular studies included ¹H-¹H ROESY NMR, ¹H NMR titration, Fourier-transform infrared spectroscopy, cyclic voltammetry, fluorescence spectra titration, and ¹H DOSY NMR. ¹H DOSY NMR was also employed to evaluate the apparent binding constants for all the complexes. The ferrocene-acyclovir conjugate Fc-5 featured the highest apparent binding constant value among all the complexes tested.

Bio-inspired nano-engineered strip for semiquantitative FeNO analysis

A point-of-care, non-invasive, low-cost and sensitive nano-biodiagnostic is needed in today's age for rapid and accurate self-diagnosis as well as for the management of asthma, which is advantageous for low resource areas where asthma is prevalent. The objective of this research work was to prepare the miniature, nanosponges coated paper strip to detect the asthma using certain biomarkers present in exhaled air. The asthma biomarker, nitric oxide present in exhaled air (FeNO) was chosen, which on reaction with nanosponges of diazotizing agent gave significant color change. The pyromellitic anhydride cross-linked β-cyclodextrin-based nanosponges of sulfanilamide and N-(1-naphthyl) ethylenediamine dihydrochloride were prepared using a polymer condensation method and coated on Whatman filter paper strip (1 × 5 cm2). The thickness of coating was found to be uniform (400 ± 50 μm) which was determined using SEM analysis. The Hue-Saturation-Value scale was used to detect the color change using a smartphone app. We also investigated the performance of a nano-engineered paper strip by comparing this with commercially available, FDA approved FeNO analyzer-NIOX MINO. Our findings demonstrated no significant difference in results obtained using both the techniques. Besides good repeatability, the paper strip showed increasing saturation with NO concentration and the capacity to detect the biomarker down to mean value of 20.33 ppb level. The successful validation and method comparison indicated that a bioinspired strip can provide on-site analysis and daily monitoring for diagnosis and management of asthma.

Atorvastatin calcium inclusion complexation with polysaccharide arabinogalactan and saponin disodium glycyrrhizate for increasing of solubility and bioavailability

The aim of the present investigation was to enhance the solubility and dissolution of atorvastatin calcium (ATV), a poorly water-soluble drug with larch polysaccharide arabinogalactan (AG) and disodium glycyrrhizate (Na₂GA) as carriers of drug delivery systems for improving its bioavailability. The interactions of ATV with AG or Na₂GA were investigated by DSC, XRD, SEM, and NMR techniques. The molecular weights of supramolecular systems-inclusion complexes and micelles-which are the hosts for ATV molecules were measured. On the other hand, the rapid storage assay (+ 40 °C for 3 months) showed that the chemical stability of ATV/AG and ATV/Na₂GA complexes had been enhanced compared with pure ATV. In vitro drug release showed a significant increase in ATV's dissolution rate after formation of a complex with Na₂GA or AG. Pharmacokinetic tests in vivo on laboratory animals showed a significant increase in ATV's bioavailability after its introduction as a complex with Na₂GA or AG. Moreover, ATV/AG and ATV/Na₂GA complexes showed a more prominent decrease of total cholesterol (TC) level compared to net ATV. Therefore, the novel mechanochemically synthesized complexes of ATV with AG or Na₂GA as drug delivery systems might be potential and promising candidates for hypercholesterolemia treatment and deserved further researches.

Enhanced Solubility of Telmisartan Phthalic Acid Cocrystals within the pH Range of a Systemic Absorption Site

Telmisartan (TLM), a nonpeptide angiotensin II antagonist, is widely prescribed for treating arterial hypertension and marketed by the innovator with the trade name of Micardis and Micardis plus. Telmisartan exhibits low aqueous solubility in the pH range of 3-7, which is the physiological pH. For addressing the issue of poor solubility of TLM, its commercial form makes use of inorganic alkalinizers. The present work illustrates the attempt to improve the solubility of telmisartan via a crystal engineering approach. A novel solid form of telmisartan with phthalic acid was obtained through the solution crystallization method (TPS) and the reaction crystallization method (TPR). Both the forms (TPS and TPR) were thoroughly characterized by powder diffraction X-ray diffraction, differential scanning calorimetry, thermogravimetric analysis, Fourier transform infrared spectroscopy, and ¹H NMR and were identified to be two different crystalline forms. Solubility studies of TPS and TPR were conducted at varying pH of phosphate buffer, and they exhibited 11-fold and 22-fold increased solubility, respectively, when compared to that of the pure drug at pH 5, which is within the pH of small intestine at which telmisartan is best absorbed orally from the systemic circulation.

Grinding as Solvent-Free Green Chemistry Approach for Cyclodextrin Inclusion Complex Preparation in the Solid State

Among the different techniques proposed for preparing cyclodextrin inclusion complex in the solid state, mechanochemical activation by grinding appears as a fast, highly efficient, convenient, versatile, sustainable, and eco-friendly solvent-free method. This review is intended to give a systematic overview of the currently available data in this field, highlighting both the advantages as well as the shortcomings of such an approach. The possible mechanisms involved in the inclusion complex formation in the solid state, by grinding, have been illustrated. For each type of applied milling device, the respective process variables have been examined and discussed, together with the characteristics of the obtained products, also in relation with the physicochemical characteristics of both the drug and cyclodextrin subjected to grinding. The critical process parameters were evidenced in order to provide a useful guide for a rational selection of the most suitable conditions for an efficient inclusion complex preparation by grinding, with the final purpose of promoting a wider use of this effective solvent-free cyclodextrin inclusion complex preparation method in the solid state.

Therapeutic evolution of benzimidazole derivatives in the last quinquennial period

Benzimidazole, a fused heterocycle bearing benzene and imidazole has gained considerable attention in the field of contemporary medicinal chemistry. The moiety is of substantial importance because of its wide array of pharmacological activities. This nitrogen containing heterocycle is a part of a number of therapeutically used agents. Moreover, a number of patents concerning this moiety in the last few years further highlight its worth. The present review covers the recent work published by scientists across the globe during last five years.

Cyclodextrin-based telmisartan ophthalmic suspension: Formulation development for water-insoluble drugs

In this study, cyclodextrin-based aqueous eye drop suspension of the water insoluble drug telmisartan was developed. Formation of a drug/γ-cyclodextrin complex was enabled by preventing formation of a poorly water-soluble zwitterion using a volatile base that was removed upon drying of the complex powder. Hydroxypropyl methylcellulose was shown to have the overall best effect, stabilizing the complexes without hampering the drug release from the formulation. Two strategies for preparing cyclodextrin-based aqueous eye drop suspensions of telmisartan were investigated, one where hydroxypropyl methylcellulose was added to the medium during preparation of the drug/γ-cyclodextrin complex powder (ternary complex) and the other where hydroxypropyl methylcellulose was added to the complex powder after preparation of the complex (binary complex). The complexation was characterized by DSC, FT-IR and (1)H NMR and the eye drop suspensions formed were examined regarding their stability and in vitro mucoadhesion property. The ternary complex exhibited inferior mucoadhesive property compared to the binary complex. However, the ternary complex was more stable as no notable change in particle size and particle size distribution was observed during storage at 4°C over 6 months (p<0.05) with the mean particle size determined between 2.0 and 2.5μm.

Changes in the Physicochemical Properties of Piperine/β-Cyclodextrin due to the Formation of Inclusion Complexes

Piperine (PP) is a pungent component in black pepper that possesses useful biological activities; however it is practically insoluble in water. The aim of the current study was to prepare a coground mixture (GM) of PP and β-cyclodextrin (βCD) (molar ratio of PP/βCD = 1/1) and subsequently evaluate the solubility of PP and physicochemical properties of the GM. DSC thermal behavior of the GM showed the absence of melting peak of piperine. PXRD profile of the GM exhibited halo pattern and no characteristic peaks due to PP and βCD were observed. Based on Job's plot, the PP/βCD complex in solution had a stoichiometric ratio of 1/1. Raman spectrum of the GM revealed scattering peaks assigned for the benzene ring (C=C), the methylene groups (CH₂), and ether groups (C-O-C) of PP that were broaden and shifted to lower frequencies. SEM micrographs showed that particles in the GM were agglomerated and had rough surface, unlike pure PP and pure βCD particles. At 15 min of dissolution testing, the amount dissolved of PP in the GM was dramatically increased (about 16 times) compared to that of pure PP. Moreover the interaction between PP and βCD cavity was detected by ¹H-¹H NMR nuclear Overhauser effect spectroscopy NMR spectroscopy.

Co-milling of telmisartan with poly(vinyl alcohol)--An alkalinizer free green approach to ensure its bioavailability

The aim of this study was to enhance the dissolution and bioavailability of telmisartan (TLM), a poorly water soluble drug by co-milling approach. Physical mixtures of TLM and poly(vinyl alcohol) (PVA) were co-milled in a planetary micro mill in a dry condition by varying process parameters such as drug to polymer weight ratio, ball-to-powder weight ratio, and rotational speed. The co-milled products offered cumulative percentage dissolution of TLM above 75% in 30 min (CG 1 and CG2). These samples were characterized using field emission scanning electron microscopy (FE-SEM), powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC) and Raman spectra analysis. Well-dispersed acicular shaped particles of TLM were observed in co-milled products. A mixture of crystalline and amorphous TLM with a particle size less than 1 μm was present in CG1. The particle size of TLM observed in CG2 was less than 2 μm. In addition to crystalline and amorphous form of TLM, defective/disordered crystals of TLM were also present in CG 2. Therefore, CG2 tablets exhibited poor stability. CG 1 tablets were found to be stable under accelerated stability test conditions. The relative bioavailability of TLM of CG 1 containing tablets in comparison with Micardis® was 93.92±12.84% (in rabbits). Thus, co-milling of TLM with PVA proves to be a promising "alkalinizer free green approach" to ensure the dissolution and bioavailability of poorly water soluble TLM.

Cyclodextrins in pharmaceutical formulations II: solubilization, binding constant, and complexation efficiency

Cyclodextrins are cyclic oligosaccharides that have been recognized as pharmaceutical adjuvants for the past 20 years. The molecular structure of these glucose derivatives, which approximates a truncated cone, bucket, or torus, generates a hydrophilic exterior surface and a nonpolar interior cavity. Cyclodextrins can interact with appropriately sized drug molecules to yield an inclusion complex. These noncovalent inclusion complexes offer a variety of advantages over noncomplexed forms of a drug. Cyclodextrins are carbohydrates that are primarily used to enhance the aqueous solubility, physical chemical stability, and bioavailability of drugs. Their other applications include preventing drug-drug interactions, converting liquid drugs into microcrystalline powders, minimizing gastrointestinal and ocular irritation, and reducing or eliminating unpleasant taste and smell. Here, we focus on the solubilization of drugs by complexation, and discuss the determination and significance of binding constants for cyclodextrin complexes, and the determination of complexation efficiency and factors that influence it. We also make some general observations on cyclodextrin complexation and the use of cyclodextrins in solid, as well as parenteral, dosage forms.