Evaluation of solubility parameter to predict apparent solubility of amorphous and crystalline cefditoren pivoxil

Development of a probucol-releasing antithrombogenic drug eluting stent

The success of drug eluting stents (DESs) has been challenged by the manifestation of late stent thrombosis after DES implantation. The incomplete regeneration of the endothelial layer poststenting triggers adverse signaling processes precipitating in thrombosis. Various approaches have been attempted to prevent thrombosis, including the delivery of biological agents, such as estradiol, that promote endothelialization, and the use of natural polymers as coating materials. The underlying challenge has been the inability to release the biological agent in synchronization with the temporal sequence of vascular wound healing in vivo. The natural healing process of the endothelium after an injury starts after a week and may take up to a month in humans. This article presents a novel DES formulation using a hemocompatible polyurethane (PU) matrix to sustain the release of probucol (PB), an endothelial agonist, by exploiting the greater difference in the solubility parameters of PB and PU. This results in the formation of crystalline PB aggregates retarding drug release from PU. The physicochemical properties of PB in PU were confirmed using differential scanning calorimetry and X-ray diffraction. Drug-polymer compatibility was examined using infrared spectral analysis. Also, in vitro studies using primary human aortic endothelial cells resulted in the selection of 5% w/w PB as the optimal dose, to be further tested in vitro and in vivo. This work develops and tests a promising new DES formulation to enable faster endothelial cell proliferation poststenting, potentially minimizing the incidence and severity of thrombotic events after DES implantation.

Kinetic solubility and dissolution velocity of rutin nanocrystals

Lyophilized rutin nanocrystals were intensively evaluated regarding their physicochemical properties with respect to particle size analyses, crystallinity, kinetic solubility and dissolution behavior. The particle size was determined by photon correlation spectroscopy (PCS) and laser diffraction (LD). DSC and X-ray diffraction were used to study the crystalline state of rutin nanocrystals. In a period of 1 week, the kinetic solubility was determined using a shaker at 25 degrees C. DSC and X-ray diffraction analyses showed that lyophilized rutin nanocrystals prepared by high pressure homogenization remained in crystalline state. Lyophilized rutin nanocrystals could be re-dispersed completely in water and the kinetic solubility in water increased to 133 microg/ml.. Lyophilized rutin nanocrystals were almost completely dissolved within 15 min in water, buffer of pH 1.2 and buffer of pH 6.8. In contrast, only 70% of rutin raw material (rutin microcrystals) was dissolved within 15 min. The superior physicochemical properties of rutin nanocrystals should overcome the absorption problem in the gastrointestinal tract and increase the bioavailability.

Analytical techniques for quantification of amorphous/crystalline phases in pharmaceutical solids

The existence of different solid-state forms such as polymorphs, solvates, hydrates, and amorphous form in pharmaceutical drug substances and excipients, along with their downstream consequences in drug products and biological systems, is well documented. Out of these solid states, amorphous systems have attracted considerable attention of formulation scientists for their specific advantages, and their presence, either by accident or design is known to incorporate distinct properties in the drug product. Identification of different solid-state forms is crucial to anticipate changes in the performance of the material upon storage and/or handling. Quantitative analysis of physical state is imperative from the viewpoint of both the manufacturing and the regulatory control aimed at assuring safety and efficacy of drug products. Numerous analytical techniques have been reported for the quantification of amorphous/crystalline phase, and implicit in all quantitative options are issues of accuracy, precision, and suitability. These quantitative techniques mainly vary in the properties evaluated, thus yielding divergent values of crystallinity for a given sample. The present review provides a compilation of the theoretical and practical aspects of existing techniques, thereby facilitating the selection of an appropriate technique to accomplish various objectives of quantification of amorphous systems.

Precision and detection limit of quality test for amorphous drug in powder X-ray diffractometry

This report puts forward a method of powder X-ray diffractometry to estimate the precision and detection limit of the crystalline component in an amorphous drug. Cefditoren pivoxil (CP) was employed as a model drug. The major error source of the measurement at low crystal contents is shown to be the random noise in a diffraction pattern (halo pattern) of the amorphous material. For the analysis of the noise, the obstructive halo pattern should be eliminated from the observed pattern. The subtraction of the observed halo pattern from another one derived from the same material, extracts the random noise alone, although the noise is amplified by square root 2 times. The noise in the powder X-ray diffractometry was identified as the white noise. On the basis of the stochastic properties of the extracted noise and signal parameters (peak area) of CP, the relative standard deviations (R.S.D.) of the area measurements of the crystalline diffraction peaks were estimated over a wide range of crystal contents without repeated experiments. The detection limit was determined such that the crystal content at detection limit produced 30% R.S.D. of the measurements. The R.S.D. and detection limit obtained from FUMI theory were in good agreement with the results from the repeated measurements.

Determination of the changes in surface energetics of cefditoren pivoxil as a consequence of processing induced disorder and equilibration to different relative humidities

The change in surface energy of cefditoren pivoxil powder as a consequence of changes in crystallinity (caused by milling duration) was studied using inverse gas chromatography (IGC) under dry conditions. The surface of the powder became more basic with decreasing crystallinity. It was suggested by considering the results of IR spectra that this resulted from exposure of the carbonyl groups, which have electron donating nature, on the particle surface. There was a direct correlation between surface energy and the % amorphous content induced during milling, giving the opportunity to use IGC to quantify amorphous content for this material. Furthermore, the changes in the acidic and basic properties on the surface of amorphous cefditoren pivoxil powder were investigated using IGC under various relative humidities (RHs). The basic nature on the surface of amorphous cefditoren pivoxil decreased with increasing RH, with a dramatic fall between 0 and 10% RH, this was attributed to water preferentially shielding the exposed carbonyl groups from acidic polar probes. Since water molecules would be adsorbed to the most hydrophilic sites at initial RH increment, it seems reasonable to suppose that the most hydrophilic adsorption sites on the surface of amorphous cefditoren pivoxil are the exposed carbonyl groups.

Water vapor adsorption properties of amorphous cefditoren pivoxil evaluated by adsorption isotherms and microcalorimetry

Water vapor adsorption of ground cefditoren pivoxil was studied. The amount of water adsorbed increased with a decrease in the crystallinity of cefditoren pivoxil. It was found from the microcalorimetric measurements that the differential heat of water vapor adsorption at 1.5% adsorbed water increased with decreasing crystallinity of cefditoren pivoxil, suggesting that hygroscopicity of cefditoren pivoxil was enhanced by grinding. These results indicated that hydrophilic adsorption sites in cefditoren pivoxil increased through the grinding process. The results of infrared (IR) spectra examination suggested that the increment of hydrophilic adsorption sites through the grinding process resulted from the change of the environment of the carbonyl groups in two esters and amide.