Preparation and characterization of ibuprofen microspheres.

Ibuprofen was microencapsulated with Eudragit RS using an o/w emulsion solvent evaporation technique. The effects of three formulation variables including the drug:polymer ratio, emulsifier (polyvinyl alcohol) concentration and organic solvent (chloroform) volume on the entrapment efficiency and microspheres size distribution were examined. The drug release rate from prepared microspheres and the release kinetics were also studied. The results demonstrated that microspheres with good range of particle size can be prepared, depending on the formulation components. The drug:polymer ratio had a considerable effect on the entrapment efficiency. However, particle size distribution of microspheres was more dependent on the volume of chloroform and polyvinyl alcohol concentration rather than the drug:polymer ratio. The drug release pattern showed a burst effect for all prepared microspheres due to the presence of uncovered drug crystals on the surface. It was shown that the release profiles of all formulations showed good correlation with the Higuchi model of release.

Crystal modification of phenytoin using different solvents and crystallization conditions.

Phenytoin crystals having different types of habits, were prepared by recrystallization from ethanol and acetone solutions under different conditions (cooling rate or crystallization temperature, solvent evaporation and watering-out techniques). Scanning electron microscopy, X-ray powder diffractometry, FT-IR spectrometry and differential scanning calorimetry were used to investigate the physical characteristics of the crystals. The dissolution behavior and compaction properties of various batches of crystals were also studied. It was found that using watering-out technique as a crystallization method, produced thin plate crystals, while the crystals obtained by other methods were needle shape for alcoholic solutions and rhombic for acetone solutions. X-ray diffraction spectra and differential scanning calorimetry studies, did not show any polymorphic change. The dissolution rate of different crystals was lower than that of untreated samples. The compacts of phenytoin crystals produced from alcohol or acetone (especially those made by watering-out method) had higher crushing strengths than untreated phenytoin compacts due to the lower porosity and the lower elastic recovery.

Effects of hydrophilic excipients and compression pressure on physical properties and release behavior of aspirin-tableted microcapsules.

Aspirin ethylcellulose microcapsules were tableted by compression with or without excipients (lactose or polyvinylpyrrolidone [PVP]). The effects of the amount of the excipients and microcapsule size on the crushing strength and release rate of aspirin from tableted microcapsules were investigated. Tablets without excipients had a crushing strength that was independent of the applied pressure and microcapsule size. An increase in compression pressure from 15 to 60 MPa resulted in an increase in the crushing strength of tablets containing 20% or 40% w/w lactose, but the reverse results were obtained for the tableted microcapsules containing 20% or 40% w/w PVP. Results showed that the release rate of aspirin from microcapsules containing lactose or PVP was independent of the compression pressure with the exception of tablets containing 40% w/w lactose. In vitro release profiles of aspirin from tableted microcapsules containing lactose or PVP showed that increasing the concentration of the excipients resulted in an increase in the release rate of aspirin. Values of n were changed by the compression pressure and the added excipients.