Some Factors Influencing the Dissolution of Solid Dispersions with Nicotinamide and Hydroxypropylmethylcellulose as Combined Carriers.

Premi

et al. 2013

JAD

Section: Discussionmentioning

confidence: 99%

Overlap between Frontotemporal Dementia and Alzheimer's Disease: Cerebrospinal Fluid Pattern and Neuroimaging Study

Premi

et al. 2013

JAD

“…22 The preparation and storage conditions of the solid dispersions play a critical role, as changes may alter the dissolution characteristics of the active ingredients over time. [35][36][37][38][39][40][41] Drugs dispersed in the amorphous phase are expected to be more soluble than the crystalline or polymorphic forms. However, amorphous drugs are less stable and more sensitive to physical alterations during storage.…”

Section: Characterization Of Solid Dispersionsmentioning

confidence: 99%

Characterization of the distribution, polymorphism, and stability of nimodipine in its solid dispersions in polyethylene glycol by micro-Raman spectroscopy and powder x-ray diffraction

Docoslis

Huszarik

Papageorgiou

et al. 2007

AAPS J

In the present study, a series of solid dispersions of the drug nimodipine using polyethylene glycol as carrier were prepared following the hot-melt method. Micro-Raman spectroscopy in conjunction with X-ray powder diffractometry was used for the characterization of the solid structure, including spatial distribution, physical state, and presence of polymorphs, as well as storage stability of nimodipine in its solid formulations. The effect of storage time on drug stability was investigated by examination of the samples 6 months and 18 months after preparation. Confocal microRaman mapping performed on the samples showed that the drug was not uniformly distributed on a microscopic level. The presence of crystals of nimodipine with sizes varying between one and several micrometers was detected, and the crystal size seemed to increase with overall drug content. In samples examined 6 months after preparation it was found that the crystals existed mainly as the racemic compound, whereas after 18 months of storage mainly crystal conglomerates were observed.

“…[14][15][16][17][18][19] Methods for monitoring the stability of the amorphous state of the drug dispersed in the polymer have been explored for a long time. Wideangle x-ray diffractometry (WAXD), differential scanning calorimetry (DSC), differential thermoanalysis, solution calorimetry, infrared spectroscopy, and Fourier Transform (FT)-Raman spectroscopy are used.…”

Section: Introductionmentioning

confidence: 99%

Effect of physical state and particle size distribution on dissolution enhancement of nimodipine/PEG solid dispersions prepared by melt mixing and solvent evaporation

Papageorgiou

Bikiaris

Karavas

et al. 2006

AAPS J

The physical structure and polymorphism of nimodipine were studied by means of micro-Raman, WAXD, DSC, and SEM for cases of the pure drug and its solid dispersions in PEG 4000, prepared by both the hot-melt and solvent evaporation methods. The dissolution rates of nimodipine/PEG 4000 solid dispersions were also measured and discussed in terms of their physicochemical characteristics. MicroRaman and WAXD revealed a signifi cant amorphous portion of the drug in the samples prepared by the hot-melt method, and that saturation resulted in local crystallization of nimodipine forming, almost exclusively, modifi cation I crystals (racemic compound). On the other hand, mainly modifi cation II crystals (conglomerate) were observed in the solid dispersions prepared by the solvent evaporation method. However, in general, both drug forms may appear in the solid dispersions. SEM and HSM microscopy studies indicated that the drug particle size increased with drug content. The dissolution rates were substantially improved for nimodipine from its solid dispersions compared with the pure drug or physical mixtures. Among solid dispersions, those resulting from solvent coevaporation exhibited a little faster drug release at drug concentrations lower than 20 wt%. Drug amorphization is the main reason for this behavior. At higher drug content the dissolution rates became lower compared with the samples from melt, due to the drug crystallization in modifi cation II, which results in higher crystallinity and increased particle size. Overall, the best results were found for low drug content, for which lower drug crystallinity and smaller particle size were observed.