Complexation of phenytoin with some hydrophilic cyclodextrins: effect on aqueous solubility, dissolution rate, and anticonvulsant activity in mice

Improvement of solubility, dissolution, and bioavailability of phenytoin intercalated in Mg-Al layered double hydroxide

Layered double hydroxides (LDHs) are highly effective drug delivery systems, owing to their capacity to intercalate or adsorb biomaterials, flexible structure, swelling property, high stability, good biocompatibility, and ease of synthesis. Phenytoin (PHT) is an antiseizure BCS (Biopharmaceutics Classification System) class II drug, presenting low aqueous solubility. Therefore, the current study aimed at increasing its solubility, dissolution, and bioavailability. PHT was intercalated to the MgAl-LDH formed in situ and successful intercalation to form MgAl-PHT-LDH was confirmed by FTIR, PXRD, DSC, and TGA. Examination of particle size and morphology (by photon correlation spectroscopy and electron microscopy, respectively) confirmed the formation and intercalation of nanostructured LDH. Intercalation enhanced the saturation solubility of PHT at 25°C in 0.1N HCl and phosphate buffer (pH 6.8) by 6.57 and 10.5 times respectively. The selected drug excipient powder blend for the formulation of MgAl-PHT-LDH tablets exhibited satisfactory properties in both pre-compression parameters (angle of repose, bulk density, tapped density, Carr's index, and Hausner ratio) and tablet characteristics (weight variation, thickness, hardness, friability, content uniformity, and disintegration time). MgAl-PHT-LDH tablets showed better dissolution of PHT compared to unprocessed PHT tablets at all time points. Oral bioavailability of MgAl-PHT-LDH tablets and unprocessed PHT tablets was tested in two groups of Sprague Dawley rats based on analysis of serum levels of both forms of PHT by UPLC-ESI-MS/MS serum. MgAl-PHT-LDH tablets demonstrated a relative bioavailability of 130.15% compared to unprocessed PHT tablets, confirming a significantly higher oral bioavailability of MgAl-PHT-LDH. In conclusion, MgAl-PHT-LDH could provide a strategy for enhancing solubility, dissolution, and thereby bioavailability of PHT, enabling the evaluation of theclinical efficacy of MgAl-PHT-LDH tablets for the treatment of seizures at lower PHT doses.

Cyclodextrins in Parenteral Formulations

Most drugs have very limited solubility in water and some can be extremely difficult to formulate as parenteral solutions where the dose should preferably be dissolved in couple of ml of aqueous media without use of organic solvents and surface active agents, or application of somewhat extreme techniques such as prodrug formation. Thus, pharmaceutical formulators are constantly looking for new, biologically acceptable, and low-cost armamentarium for parenteral formulation development. Cyclodextrins (CDs) are enabling pharmaceutical excipients that can temporarily camouflage undesirable physiochemical drug properties such as low aqueous solubility through formation of drug/CD inclusion complexes. CDs are cyclic oligosaccharides that have similar physiological and biological properties like linear saccharides of comparable molecular weight. Due to their very favorable toxicological and pharmacokinetic profiles their usage in parenteral drug formulations is frequently preferred over other solubilizing techniques. Here the physiochemical and biological properties of CDs are reviewed as well as their pharmacokinetics after intravenous administration. Their regulatory status is briefly reviewed and their tendency to self-assemble to form clusters or aggregates discussed. Finally, some examples are given of how CDs are applied in aqueous parenteral formulations, how their solubilizing effect has been enhanced and how their target concentration is determined.

An overview of techniques for multifold enhancement in solubility of poorly soluble drugs

Poor water solubility of newly discovered compounds has become the most common challenge in the drug development process. Indeed, poor solubility is considered as the root cause of failure of drug during drug development phases. Moreover, it has also been reported to be the main reason for bioavailability issues such as poor, inconsistent, incomplete and highly variable bioavailability of the marketed products. As per an estimate, approximately 90% of drug molecules suffer with poor water solubility at early stage and approximately 40% of the marketed drugs have bioavailability problems mainly due to poor water solubility. Solubility enhancement of the newly discovered compounds is primary research area for the pharmaceutical industries and research institutions. The conventional techniques to improve aqueous solubility of drugs employ salt formation, prodrug formation, co-crystallization, complexation, amorphous solid dispersion and use of co-solvent, surfactants or hydrotropic agents. Current advancement in the science and technology has enabled the use of relatively new techniques under the umbrella of nanotechnology. These include the development of nanocrystals, nanosuspensions, nanoemulsions, microemulsions, liposomes and nanoparticles to enhance the solubility. This review focuses on the conventional and current approaches of multifold enhancement in the solubility of poorly soluble marketed drugs, including newly discovered compounds.

New ethanol and propylene glycol free gel formulations containing a minoxidil-methyl-β-cyclodextrin complex as promising tools for alopecia treatment

New topical totally aqueous formulations that improve the low water solubility of minoxidil and realize an adequate permeability of drug in the skin are proposed. These formulations are lacking in propylene glycol and alcohol that are the principal irritant ingredients present in minoxidil commercial solutions. In order to enhance poor water solubility of minoxidil randomly methyl-β-cyclodextrin was used, and four hydrogels such as, calcium alginate, sodium alginate, carbopol 934 and hydroxyethylcellulose were utilized to ensure a prolonged time of contact with the scalp. The inclusion complex minoxidil/methyl-β-cyclodextrin with a molar ratio 1:1 was obtained by freeze drying and evaluated by NMR, FT-IR and DSC analysis. An apparent stability constant of formed inclusion complex was calculated by phase solubility diagram and its value was 400 M(-1). The solid inclusion complex was used to prepare gel formulations with similar dose to minoxidil commercial solution. The gels were evaluated for various technological parameters including rheological behavior, in vitro drug release and ex vivo permeation through pig skin. The best performance was observed for the calcium alginate formulation.

Formulation and evaluation of fixed-dose combination of bilayer gastroretentive matrix tablet containing atorvastatin as fast-release and atenolol as sustained-release

The objective of the present study was to develop bilayer tablets of atorvastatin and atenolol that are characterized by initial fast-release of atorvastatin in the stomach and comply with the release requirements of sustained-release of atenolol. An amorphous, solvent evaporation inclusion complex of atorvastatin with β-cyclodextrin, present in 1 : 3 (drug/cyclodextrin) molar ratio, was employed in the fast-release layer to enhance the dissolution of atorvastatin. Xanthan gum and guar gum were integrated in the sustained-release layer. Bilayer tablets composed of sustained-release layer (10% w/w of xanthan gum and guar gum) and fast-release layer [1 : 3 (drug/cyclodextrin)] showed the desired release profile. The atorvastatin contained in the fast-release layer showed an initial fast-release of more than 60% of its drug content within 2 h, followed by sustained release of the atenolol for a period of 12 h. The pharmacokinetic study illustrated that the fast absorption and increased oral bioavailability of atorvastatin as well as therapeutic concentration of atenolol in blood were made available through adoption of formulation strategy of bilayer tablets. It can be concluded that the bilayer tablets of atorvastatin and atenolol can be successfully employed for the treatment of hypertension and hypercholesterolemia together through oral administration of single tablet.

Advanced technologies for oral controlled release: cyclodextrins for oral controlled release

Cyclodextrins (CDs) are used in oral pharmaceutical formulations, by means of inclusion complexes formation, with the following advantages for the drugs: (1) solubility, dissolution rate, stability, and bioavailability enhancement; (2) to modify the drug release site and/or time profile; and (3) to reduce or prevent gastrointestinal side effects and unpleasant smell or taste, to prevent drug-drug or drug-additive interactions, or even to convert oil and liquid drugs into microcrystalline or amorphous powders. A more recent trend focuses on the use of CDs as nanocarriers, a strategy that aims to design versatile delivery systems that can encapsulate drugs with better physicochemical properties for oral delivery. Thus, the aim of this work was to review the applications of the CDs and their hydrophilic derivatives on the solubility enhancement of poorly water-soluble drugs in order to increase their dissolution rate and get immediate release, as well as their ability to control (to prolong or to delay) the release of drugs from solid dosage forms, either as complexes with the hydrophilic (e.g., as osmotic pumps) and/or hydrophobic CDs. New controlled delivery systems based on nanotechnology carriers (nanoparticles and conjugates) have also been reviewed.

Cyclodextrins in delivery systems: Applications

Cyclodextrins (CDs) are a family of cyclic oligosaccharides with a hydrophilic outer surface and a lipophilic central cavity. CD molecules are relatively large with a number of hydrogen donors and acceptors and, thus in general, they do not permeate lipophilic membranes. In the pharmaceutical industry, CDs have mainly been used as complexing agents to increase aqueous solubility of poorly soluble drugs and to increase their bioavailability and stability. CDs are used in pharmaceutical applications for numerous purposes, including improving the bioavailability of drugs. Current CD-based therapeutics is described and possible future applications are discussed. CD-containing polymers are reviewed and their use in drug delivery is presented. Of specific interest is the use of CD-containing polymers to provide unique capabilities for the delivery of nucleic acids. Studies in both humans and animals have shown that CDs can be used to improve drug delivery from almost any type of drug formulation. Currently, there are approximately 30 different pharmaceutical products worldwide containing drug/CD complexes in the market.

Complexation of tanshinone IIA with 2-hydroxypropyl-beta-cyclodextrin: effect on aqueous solubility, dissolution rate, and intestinal absorption behavior in rats

In this paper, the effect of 2-hydroxypropyl-beta-cyclodextrin (HP-beta-CD) on the aqueous solubility, dissolution rate, and intestinal permeability of the tanshinone IIA (TS IIA) was investigated. The corresponding inclusion complex of TS IIA/HP-beta-CD at the molar ratio of 1:1 was obtained by coevaporation and characterized by differential scanning calorimetry, and X-ray diffraction. The solubility of complexed TS IIA in water at 37+/-0.1 degrees C was 17 times greater than that for the uncomplexed drug. The dissolution rate of TS IIA was significantly increased by the complexation with HP-beta-CD, due to its solubilizing activity. The everted intestinal sac technique in rats was used to study the absorption behavior of TS IIA and this complexation through the intestinal tissues. The permeability rates of TS IIA across the intestinal epithelial membrane were enhanced by the formation of inclusion complex with HP-beta-CD about 5.2, 5.8 and 4.8 times of the uncomplexed TS IIA in duodenum, jejunum and ileum, respectively. It was revealed that the absorption rate-limiting step of TS IIA might be the dissolution process. The present results indicate the potential use of HP-beta-CD to improve the gastrointestinal tract absorption of TS IIA.

Cyclodextrins in drug delivery: an updated review

The purpose of this review is to discuss and summarize some of the interesting findings and applications of cyclodextrins (CDs) and their derivatives in different areas of drug delivery, particularly in protein and peptide drug delivery and gene delivery. The article highlights important CD applications in the design of various novel delivery systems like liposomes, microspheres, microcapsules, and nanoparticles. In addition to their well-known effects on drug solubility and dissolution, bioavailability, safety, and stability, their use as excipients in drug formulation are also discussed in this article. The article also focuses on various factors influencing inclusion complex formation because an understanding of the same is necessary for proper handling of these versatile materials. Some important considerations in selecting CDs in drug formulation such as their commercial availability, regulatory status, and patent status are also summarized. CDs, because of their continuing ability to find several novel applications in drug delivery, are expected to solve many problems associated with the delivery of different novel drugs through different delivery routes.

Valproic Acid‐Hydrophilic Cyclodextrin Complexes and Valproic Acid‐Solid Dispersions: Evaluation of Their Potential Pharmaceutical Use

The purpose of this study was to evaluate the potential use of two novel solid formulations of valproic acid (VPA) prepared by complexation with hydrophilic cyclodextrins (CDs) as hydroxypropyl-beta- and sulfobutylether-beta-cyclodextrin and by solid dispersion (SD) in hydrophilic carriers as polyethylene glycol 6000 (PEG 6000) and polyvinylpyrrolidone K-30 (PVP K-30). The corresponding cyclodextrin-based complexes were prepared by the freeze-drying method while the solid dispersions were obtained by the solvent method. Valproic acid solubility improved by CDs complexation and solid dispersion techniques. Comparison of dissolution profiles with that of VPA sodium salt (NaVP) was made by using release parameters such as dissolution efficiency, percent of drug dissolved after 60 min, and difference and similarity factors. Based on difference and similarity factors, it can be concluded that all the VPA formulations possess dissolution profiles essentially equivalent to those of NaVP at pH 6. However, this conclusion is not confirmed by using the analysis of variance (ANOVA) approach, indicating some significant differences between some SD-based formulations and NaVP at that pH value. Preliminary pharmacological studies in the pentylenetetrazole test in rats showed some important differences among the SD-based formulations, NaVP, and VPA as oil/water emulsion. Some implications and limitations of the investigated formulations are discussed.

Improvement of Dissolution and Bioavailability of Nitrendipine by Inclusion in Hydroxypropyl-β-cyclodextrin

A significant increase in solubility and dissolution rate of nitrendipine, a slightly soluble calcium channel blocker, was achieved by inclusion complexation with hydroxypropyl-beta-cyclodextrin (HP-beta-CD). The inclusion complex was prepared by solvent evaporation method and characterized by phase solubility method, x-ray diffractometry, infrared spectroscopy, and differential scanning calorimetry. The solubility of nitrendipine increased linearly as a function of HP-beta-CD concentration, resulting in AL-type phase solubility diagram which revealed a formation of inclusion complex in a molar ratio of 1:1, with the apparent association constant of 108.3M(-1). The in vitro dissolution rate of nitrendipine in pH 7.4 phosphate buffer was in the order of inclusion complex, physical mixture, and nitrendipine powder. These three different forms of nitrendipine were administered orally to rats with a dose of 10 mg/kg equivalent to nitrendipine. The AUC of inclusion complex was significantly larger than that of nitrendipine powder. Tmax of inclusion complex was significantly shorter and Cmax was significantly higher than those of nitrendipine powder. Cmax of physical mixture was higher than that of nitrendipine powder. Tmax of physical mixture, however, remained the same. The results indicated that the bioavailability of nitrendipine could be improved markedly by inclusion complexation, possibly due to an increased dissolution rate.

Differentiated thermal crystallization from amorphous chenodeoxycholic acid between the ground specimens derived from the polymorphs

Crystallization behavior of amorphous chenodeoxycholic acid (CDCA) was studied using X-ray diffraction (XRD), infrared (IR) spectroscopy and differential scanning calorimetry (DSC). The two polymorphs of CDCA, form I (mp 166 degrees C) and form III (mp 119 degrees C), were ground with a vibrational mill. The ground samples of both crystal forms showed halo X-ray diffraction patterns. DSC curves of the amorphous samples derived from the form I and form III showed exothermic peaks due to the crystallization to the form I at 120 and 147 degrees C, respectively. When the ground form III was mixed with the ground form I, the crystallization temperature shifted to a lower temperature as the content of the ground form I increased. In the case of co-ground sample of form I and form III, the crystallization to form I crystals proceeded by two different modes. These results indicate that the physicochemical state was different among the ground samples of the form I and form III, and that the crystal nuclei played an important role on the crystallization process of the amorphous CDCA.