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

The effect of structurally related impurities on crystallinity reduction of sulfamethazine by grinding

In this study, the effect of structurally related impurities on crystallinity reduction of sulfamethazine by grinding was evaluated. The crystallinity of sulfamethazine was not decreased when it was ground alone. However, when structurally related impurities with sulfonamide derivatives were blended, the crystallinity of sulfamethazine was decreased by grinding. Other materials without a sulfonamide moiety showed no such effect. The Raman spectra of sulfamethazine demonstrated that there was a difference between its crystalline and amorphous states within its sulfonamide structure. It was suggested that the sulfonamide structure of the impurities was important in causing the inhibition of recrystallization of sulfamethazine during grinding.

The influence of residual water on the solid-state properties of freeze-dried fibrinogen

The purpose of this work was to investigate the influence of residual water in freeze-dried protein powders on the dissolution behavior of the solid-state proteins. To that end, six freeze-dried fibrinogen powder lots were stored at four levels of relative humidity and analyzed with regard to the particle size and shape, the specific surface area, the solid state of protein and the inner surface. Furthermore, the dissolution behavior of the powders was investigated. We clearly identified differences in the specific surface area, specific inner surface area, crystallinity, particle size and shape, which we were able to correlate to the dissolution behavior. These differences were triggered due to the different levels of residual moisture during two weeks of storage. Thus, we were able to show that the storage conditions have significant impact on the processing of pharmaceutical protein materials.

Specific surface, crystallinity, and dissolution of lyophilized fibrinogen. A study by combined small- and wide-angle X-ray scattering (SWAXS)

The nano-structural properties of six different batches of lyophilized fibrinogen at various contents of residual humidity (6-20%) were studied by small- and wide-angle X-ray scattering (SWAXS) and related to the dissolution properties. As structural parameters, the specific surface and relative degree of crystallinity, from SAXS and WAXS, respectively, were used, and correlated to the dissolution rates. BET surface area and electron microscopy were used as ancillary methods. The results show a complex, biphasic behavior: above 9% water content the crystallinity increased, and the specific surface decreased with increasing water contents; at the lowest water contents (6%), however, where the WAXS patterns showed amorphous structure of the fibrinogens, the specific surface and dissolution rates diverged over a wide range of values. Systematic correlations could be established between specific surface and dissolution rates for the water contents below 13%: the dissolution rates were found to decrease with increasing specific surface, most notably in the amorphous form, in contrast to expectations from classical thermodynamics. Protein conformational changes and hydrophobic surface formation upon depletion of water could be possible causes. This is supported by the protective effect of the high-HLB surfactant PS-80, which was found to enlarge the specific surface.

Identification of the degradation products of the steroid sulfatase inhibitor KW-2581 in jet mill-micronized powder

The novel steroid sulfatase inhibitor KW-2581 is poorly soluble in water, and jet milling was used in an attempt to increase its oral bioavailability. Unfortunately, however, the milled powder exhibited poorer qualities than the intact sample, including a lower level of crystallinity, higher water content, and increased decomposition rate. A comprehensive study of the jet milled sample was performed to identify the impurities and degradation mechanisms. The degradants were identified as the hydrolyzed and air-oxidized byproducts of KW-2581. The radical propagation mechanism of the oxidation reactions associated with the degradation of KW-2581 was assumed to be mediated by water or metal catalysis. The inclusion of a drying process following the micronization step allowed for the decomposition mechanism to be successfully controlled in the subsequent storage of the jet mill-micronized KW-2581 drug substance.

A study of the differences between two amorphous spray-dried samples of cefditoren pivoxil which exhibited different physical stabilities

The objective of this study was to investigate the reasons for the difference in physical stability of two amorphous cefditoren pivoxil samples that had been prepared using spray drying at inlet-air temperatures of 40 degrees C (SD-A) and 100 degrees C (SD-B). The two samples appeared amorphous by powder X-ray diffraction and had indistinguishable glass transition temperatures. Despite the fact that glass transition is often regarded as an indicator of the stability of amorphous forms, crystallisation was observed for SD-A, but not for SD-B, during storage at 60 degrees C and 81% relative humidity (RH). Gravimetric water sorption data demonstrated very similar water sorption until high RH values, at which point SD-A sorbed more water than did SD-B. The values of the dispersive, acidic (K(A)) and basic (K(D)) components of surface energy of the spray-dried samples were obtained using inverse gas chromatography (IGC), in the dry state and after equilibration with different RH environments. The data showed that the two amorphous samples had different surface properties and that the effect of sorbed water on these samples was also different. It is concluded that the two samples did not have long-range order, but had differences in the orientation of molecules at the surface, which were significant enough to alter the stability when the samples were stressed with water vapour and high temperature storage. IGC proved a valuable tool with which to study changes in the surface properties of amorphous materials.

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.