Improvement of oral bioavailability of prednisolone by beta-cyclodextrin complexation in humans

Short Review on the Biological Activity of Cyclodextrin-Drug Inclusion Complexes Applicable in Veterinary Therapy

Cyclodextrins (CDs) are a family of carrier molecules used to improve the pharmacokinetic parameters of therapeutic molecules. These cyclic oligosaccharides have medical and pharmaceutical applications by being able to form inclusion complexes with molecules that are poorly soluble in water. The benefits of these complexes are directed towards improving the chemical and biological properties-i.e., solubility, bioavailability, stability, non-toxicity and shelf life of drug molecules. Since the 1960s, the first inclusion complexes used in therapeutics were those with α-, β- and γ-CD, which proved their usefulness, but had certain degrees of particularly renal toxicity. Currently, to correct these deficiencies, β-CD derivatives are most frequently used, such as sulfobutylether-β-CD, hydroxypropyl-β-CD, etc. Therefore, it is of interest to bring to the attention of those interested the diversity of current and potential future clinical applications of inclusion complexes in veterinary medicine and to present the contribution of these inclusion complexes in improving drug efficacy. The most important biological activities of β-CD complexed molecules in the veterinary field are summarized in this short review.

Encapsulation of finasteride with native and modified γ-cyclodextrins. Extensive characterization of the complexes

The aim of this work was to study the complexation process of FIN with native and modified CDs, to develop an aqueous solution for the topical treatment of male androgenic alopecia. The effect of pH and temperature in the complexation process were studied by solubility studies. The complexes FIN-CDs were characterized by ¹HNMR and 2-D NMR (ROESY) spectroscopy. Molecular modeling studies and NMR data were used to build three-dimensional models of the complexes. FTIR, DSC and SEM techniques were also applied to strengthen physicochemical characterization, geometry as well as structural aspects evidencing the effective inclusion of FIN into the CDs' hydrophobic cavity. The most effective CDs in the FIN complexation were γ-CDs, and their modified HP-γ- and methyl-γ-CDs by forming 1:1 complexes. The Kc value obtained for γ-CDs was 9687 ± 51 M^-1, whereas the Kc values obtained for HP-γ- and methyl-γ-CDs were lower, indicating that the presence of HP or methyl groups hinder the entry of FIN in the hydrophobic cavity of γ-CDs. In conclusion, FIN aqueous solubility could be increased by complexation with CDs and the aqueous solutions obtained can be used to improve FIN therapeutic possibilities in a pleasant preparation for the patient that guarantees the adherence to the treatment.

6-Triazolyl-6-deoxy-β-cyclodextrin derivatives: synthesis, cellular toxicity, and phase-solubility study

Heptakis{6-(4-hydroxymethyl-1H-[1,2,3]triazol-1-yl)-6-deoxy}-β-cyclodextrin (HTβCD) and heptakis{6-(4-sulfonylmethyl-1H-[1,2,3]triazol-1-yl)-6-deoxy}-β-cyclodextrin (STβCD) were prepared using copper(I)-catalyzed azide-alkyne cycloaddition between 6-azido-6-deoxy-β-CD and one of two alkynes, propargyl alcohol, and sodium propargyl sulfonate, respectively. The structures of HTβCD and STβCD were characterized by NMR techniques. NMR interpretations and computer modeling suggested that the limited freedom of rotation of the triazole moieties keeps HTβCD and STβCD rigid and compact. Water solubility tests of HTβCD and STβCD showed that the minimum water solubility of HTβCD and STβCD is at least 20times higher than that of β-CD. MTT assay showed that HTβCD and STβCD did not influence the cell viability under 1mM. A phase-solubility study of prednisolone with the CD derivatives showed increased solubility of prednisolone in the presence of increasing concentrations of HTβCD and STβCD.

Cyclodextrins and ternary complexes: technology to improve solubility of poorly soluble drugs

Cyclodextrins (CDs) are cyclic oligosaccharides composed of D-glucopyranoside units linked by glycosidic bonds. Their main property is the ability to modify the physicochemical and biological characteristics of low-soluble drugs through the formation of drug:CD inclusion complexes. Inclusion complexation requires that host molecules fit completely or partially within the CD cavity. This adjustment is directly related to the physicochemical properties of the guest and host molecules, easy accommodation of guest molecules within the CD cavity, stoichiometry, therapeutic dose, and toxicity. However, dosage forms may achieve a high volume, depending on the amount of CD required. Thus, it is necessary to increase solubilization efficiency in order to use smaller amounts of CD. This can be achieved by adding small amounts of water-soluble polymers to the system. This review addresses aspects related to drug complexation with CDs using water-soluble polymers to optimize the amount of CD used in the formulation in order to increase drug solubility and reduce dosage form volume.

The utility of cyclodextrins for enhancing oral bioavailability

Cyclodextrins (CD) have been utilized extensively in pharmaceutical formulations to enhance oral bioavailability. A critical review of the literature in which cyclodextrins were utilized for this purpose was conducted. The goal of this review was to determine if quantitative guidelines for drug and cyclodextrin properties necessary for bioavailability enhancement using cyclodextrins could be extracted. Twenty-eight studies were examined in which the focus was on the use of cyclodextrins as solubilizers to enhance bioavailability. Commonly observed factors included: utilization of pre-formed complex rather than physical mixtures, drug hydrophobicity (logP > 2.5), low drug solubility (typically< 1 mg/ml), moderate binding constant (< 5000 M(-1)), low dose (< 100 mg), and low CD:drug ratio (< 2:1). These general guidelines, however, did not apply to all studies. Quantitative guidelines useful to a formulation scientist considering the use of cyclodextrins were difficult to develop due to missing information and the complicated manner in which drug and cyclodextrin properties interact to influence key drug delivery processes (e.g., dissolution, absorption). The mechanisms by which cyclodextrins influence these processes, again emphasizing solubilization capabilities, are discussed to provide further insight into why cyclodextrins will increase bioavailability in certain cases but not influence or possibly decrease bioavailability in others.

Phase solubility and structure of the inclusion complexes of prednisolone and 6 alpha-methyl prednisolone with various cyclodextrins

The purpose of this work was to study the inclusion binding interaction of two structurally related steroids, prednisolone and 6alpha-methyl prednisolone with a wide variety of cyclodextrins (CDs), both native (alpha-, beta- and gamma-CD) as well as modified (hydroxypropyl-, sulfobutyl ether-, glucosyl-, and maltosyl-beta-CD and sulfobutyl ether-gamma-CD), and to relate the binding constants to structural differences in the steroids. Phase-solubility diagrams of the steroids with various CDs were obtained. The stability constants (K1:1) revealed that beta-CD formed the strongest complex with prednisolone, followed by gamma-CD. With 6alpha-methyl prednisolone, the stability constants of both beta- and alpha-CD were considerably lower compared with prednisolone. In contrast, gamma-CD formed a stronger complex with 6alpha-methyl prednisolone compared with prednisolone. Derivatives of beta-CD gave slightly altered stability constants compared with native beta-CD. The structures of the complexes between the two guest molecules and native beta-CD were studied by nuclear magnetic resonance spectroscopy. This clearly showed that the introduction of the methyl group led to a different binding geometry of 6alpha-methyl prednisolone compared with prednisolone. Additionally, the nuclear magnetic resonance results indicate the presence of an additional, weaker binding site, which is less populated in prednisolone.

[Pharmaceutical application of cyclodextrins as multi-functional drug carriers]

Owing to the increasingly globalized nature of the cyclodextrin (CyD)-related science and technology, development of the CyD-based pharmaceutical formulation is rapidly progressing. The pharmaceutically useful CyDs are classified into hydrophilic, hydrophobic, and ionic derivatives. Because of the multi-functional characteristics and bioadaptability, these CyDs are capable of alleviating the undesirable properties of drug molecules through the formation of inclusion complexes or the form of CyD/drug conjugates. This review outlines the current application of CyDs in drug delivery and pharmaceutical formulation, focusing on the following evidences. 1) The hydrophilic CyDs enhance the rate and extent of bioavailability of poorly water-soluble drugs. 2) The amorphous CyDs such as 2-hydroxypropyl-beta-CyD are useful for inhibition of polymorphic transition and crystallization rates of drugs during storage. 3) The delayed release formulation can be obtained by the use of enteric type CyDs such as O-carboxymethyl-O-ethyl-beta-CyD. 4) The hydrophobic CyDs are useful for modification of the release site and/or time profile of water-soluble drugs with prolonged therapeutic effects. 5) The branched CyDs are particularly effective in inhibiting the adsorption to hydrophobic surface of containers and aggregation of polypeptide and protein drugs. 6) The combined use of different CyDs and/or pharmaceutical additives can serve as more functional drug carriers, improving efficacy and reducing side effects. 7) The CyD/drug conjugates may provide a versatile means for the constructions of not only colonic delivery system but also site-specific drug release system, including gene delivery. On the basis of the above-mentioned knowledge, the advantages and limitations of CyDs in the design of advanced dosage forms will be discussed.

Determination of second-order association constants by global analysis of 1H and 13C NMR chemical shifts. Application to the complexation of sodium fusidate and potassium helvolate by beta- and gamma-cyclodextrin

The host-guest interaction between the steroid antibiotics sodium fusidate and potassium helvolate as guests and the hosts beta- and gamma-cyclodextrin was studied by 13C and 1H NMR techniques. The analysis of chemical shifts of individual nuclei leads to inconsistent values of the association constants and fails generally in the case of mixtures of 1:1 and 1:2 stoichiometries. The problem of parameter correlation is identified and the global analysis of two or more nuclei is proposed as a very effective method for the detection of complexes of higher stoichiometries and for the precise determination of the involved association constants. A matrix formulation of global analysis and the determination of confidence intervals is described. An analytical solution of the cubic equation, necessary for the description of higher order complexes, is presented in detail and its use together with commercial fitting software is compared with dedicated implementations. gamma-Cyclodextrin forms with both studied steroids, sodium fusidate and potassium helvolate, 1:1 complexes with high values of the association constants, K(1)=(60+/-24)x10(3)lmol(-1), and K(2)=(22+/-9)x10(3)lmol(-1), respectively. To the contrary, beta-cyclodextrin forms 1:1 and 1:2 (guest:host) complexes with both steroids, with moderate K(1) and low K(2) values (K(1)=(0.74+/-0.13)x10(3)lmol(-1), K(2)=(0.210+/-0.075)x10(3)lmol(-1)), and (K(1)=(2.42+/-0.87)x10(3)lmol(-1), K(2)=(0.06+/-0.09)x10(3)lmol(-1)), respectively.

Liposomes encapsulating prednisolone and prednisolone-cyclodextrin complexes: comparison of membrane integrity and drug release

Inclusion complexes of prednisolone (PR) with beta-cyclodextrin (beta-CD) and hydropropyl-beta-cyclodextrin (HPbeta-CD) were formed by the solvation method, and were characterized by DSC, X-ray diffractometry and FT-IR spectroscopy. PC liposomes incorporating PR as plain drug or inclusion complex were prepared using the dehydration-rehydration method and drug entrapment as well as drug release were estimated for all liposome types prepared. The highest PR entrapment value (80% of the starting material) was achieved for PC/Chol liposomes when the HPbeta-CD-PR (2:1, mol/mol) complex was entrapped. The leakage of vesicle encapsulated 5,6-carboxyfluorescein (CF) was used as a measure of the vesicle membrane integrity. As judged from our experimental results liposomes which encapsulate beta-CD-PR complexes are significantly less stable (when their membrane integrity is considered) compared to liposomes of identical lipid compositions which incorporate plain drug or even (in some cases) non-drug incorporating liposomes, which were prepared and studied for comparison. Interestingly, liposomes which encapsulate HPbeta-CD-PR complexes, have very low initial CF latency values, indicating that the leakage of CF is a process of very high initial velocity. Interactions between lipid and cyclodextrin molecules may be possibly resulting in rapid reorganization of the lipid membrane with simultaneous fast release of CF molecules. The release of PR from liposomes was highest when the drug was entrapped in the form of a complex with beta-CD. Nevertheless, the very high entrapment ability of PR in the form of HPbeta-CD-PR complexes in comparison to plain drug is a indubitable advantage of this approach.