Physicochemical properties of amorphous roxithromycin prepared by quench cooling of the melt or desolvation of a chloroform solvate.

Roxithromycin is a poorly soluble antibacterial drug. The aim of this study was to prepare and characterize an amorphous form of roxithromycin. The amorphous form was prepared by desolvation of its chloroform solvate, and by quench cooling a melt of the crystalline monohydrated solid. The X-ray powder diffraction pattern of the desolvated chloroform solvate was indistinguishable from that of the glass prepared by melting, which indicated that it was amorphous. The roxithromycin glass was determined to be a fragile glass, but due to its high Kauzmann temperature (approximately 8°C), it should remain fairly stable upon refrigeration or even at room temperature. It was also determined that this glass remains stable in the presence of moisture with no indication of crystallization.

Comparison of the physical and chemical stability of niclosamide crystal forms in aqueous versus nonaqueous suspensions.

In an effort to produce physically stable and pharmaceutically acceptable suspensions of niclosamide, this study reports the differences in physical and chemical stability of aqueous vs. nonaqueous suspensions of a niclosamide anhydrate, two monohydrates HA and HB, a 1:1 niclosamide N,N-dimethylformamide solvate, a 1:1 niclosamide dimethyl sulfoxide solvate, a 1:1 niclosamide methanol solvate, and a 2:1 niclosamide tetraethylene glycol hemisolvate. Evaluation of aqueous and nonaqueous suspensions showed that in aqueous suspensions anhydrous, and solvated niclosamide crystal forms were transformed to a monohydrate, HA, which was reasonably stable but which did eventually transform to the most stable monohydrate HB. The order in which these crystal forms transformed to monohydrate HB were: Anhydrate > N,N-dimethylformamide > dimethyl sulfoxide > methanol > tetraethylene glycol > monohydrate HA. In a nonaqueous propylene glycol vehicle, the transformation to the monohydrous forms was not observed and on desolvation the solvated crystals transformed to the anhydrous form. In all cases, immediately upon desolvation or dehydration, the crystal structures of the desolvated materials were similar to that of the solvated materials. However, the isomorphic structures, formed after desolvation, were unstable and rehydrated or resolvated when exposed to the solvent or converted to the anhydrous form in a dry environment. The crystal forms remained chemically stable in both aqueous and nonaqueous suspensions for the length of the study.

Preparation and physicochemical characterization of 5 niclosamide solvates and 1 hemisolvate.

The purpose of the study was to characterize the physicochemical, structural, and spectral properties of the 1:1 niclosamide and methanol, diethyl ether, dimethyl sulfoxide, N,N' dimethylformamide, and tetrahydrofuran solvates and the 2:1 niclosamide and tetraethylene glycol hemisolvate prepared by recrystallization from these organic solvents. Structural, spectral, and thermal analysis results confirmed the presence of the solvents and differences in the structural properties of these solvates. In addition, differences in the activation energy of desolvation, batch solution calorimetry, and the aqueous solubility at 25 degrees C, 24 hours, showed the stability of the solvates to be in the order: anhydrate > diethyl ether solvate > tetraethylene glycol hemisolvate > methanol solvate > dimethyl sulfoxide solvate > N,N' dimethylformamide solvate. The intrinsic and powder dissolution rates of the solvates were in the order: anhydrate > diethyl ether solvate > tetraethylene glycol hemisolvate > N,N' dimethylformamide solvate > methanol solvate > dimethyl sulfoxide solvate. Although these nonaqueous solvates had higher solubility and dissolution rates than the monohydrous forms, they were unstable in aqueous media and rapidly transformed to one of the monohydrous forms.

Preparation and physicochemical properties of niclosamide anhydrate and two monohydrates.

The intent of the study was to prepare and characterize three crystal forms of niclosamide namely the anhydrate and the two monohydrates and to investigate the moisture adsorption and desorption behavior of these crystal forms. The crystal forms were prepared by recrystallization and were characterized by differential scanning calorimetry, thermogravimetric analysis, isoperibol solution calorimetry, Karl Fischer titration, and X-ray powder diffractometry. Moisture adsorption by the anhydrate at increased relative humidities and two temperatures, 30 and 40 degrees C, was measured while the desorption from the monohydrates was determined at 45, 55, and 65 degrees C for monohydrate H(A) and 75, 90, and 100 degrees C for monohydrate H(B). Thermal analysis and solution calorimetry showed that monohydrate H(B) is more stable than monohydrate H(A) and solubility measurements showed the solubility of the crystal forms decreased in the order: anhydrate>>monohydrate H(A)>monohydrate H(B). With an increase in temperature and relative humidity niclosamide anhydrate adsorbed moisture to form monohydrate H(A) by a random nucleation process. Dehydration of monohydrate H(A) at increased temperatures followed zero order kinetics and resulted in a change to the anhydrate. Monohydrate H(B) was transformed to the anhydrate at higher temperatures by a three-dimensional diffusion mechanism.