ABSTRACT
The incorporation of a drug in a carrier by either solvent evaporation or melt embedding may result in either a solid solution or a solid suspension of the active ingredient within the carrier material. Consequently, solid dispersions [SD] of rofecoxib containing varying concentrations of either polyethylene glycol [PEG] 35000 or urea were prepared in an attempt to improve the solubility and dissolution rate of rofecoxib. Moreover, the influence of the PEG chain length on the dissolution characteristics of the drug was also investigated. The physical characteristics of rofecoxib, physical mixtures iPM] and SDs were investigated by a variety of analytical methods including fourier transform infrarrd spectroscopy [FTIR], powder X-ray diffraction [XRD] and differential scanning calorimetry [DSC]. For testing the applicability to formulate in a solid dosage form, 1:9 rofecoxib SD with PEG 3500C was formulated in the form of hard gelatin capsules. The obtained results showed that the dissolution rates of PMs were higher than that of pure drug. However, SDs exhibited higher dissolution rates than those of PMs. compared to urea, PEG 35000 had the most influential effect on enhancing the rate and extent of rofecoxib dissolution from their systems. The drug to carrier ratio in the prepared SDs was one of the main influences on the performance of a SD. In addition, it was found at the fusion method was more efficient than the solvent method in improving the dissolution of the drug from the investigated SDs. Regarding the effect of the pH of the dissolution medium, it was found that the pH change had negligible effect on the release of the drug from its dispersions with PEG 35000. The FTIR spectra revealed an interaction between rofecoxib and PEG 35000. Besides, the amorphous form of rofecoxib found in powdered SDs, as demonstrated by XRD and DSC, may explain the better dissolution rate from SD
ABSTRACT
This research was performed to evaluate some physico-mechanical properties of four different types of provisional restorative materials: water sorption, color stability, flexural strength and marginal fit. The tested materials included one type of heat-processed methyl methacrylate resin, one type of auto-polymerized methyl methacrylate resin and two types of auto-polymerized resin composite [hand-mixed and auto-mixed]. As regards the water sorption test, the corrected water sorption of the disc specimens of the four investigated materials [10 mm in diameter, 2 mm in thickness] was calculated up to six weeks immersion period in distilled water. Concerning the color stability test, the disc specimens of the four tested materials [10 mm in diameter, 2 mm in thickness] were immersed in distilled water for one month the color change [AE] was calculated after one week and one month. For flexural strength test, the bar specimens [25 x 5 x 2 mm] of the four tested materials were subjected to a three point loading using the Universal Testing Machine 24 hours after polymerization. As regards the marginal fit test, a die resembling a prepared molar was constructed and the marginal gap in millimeters was measured for the four tested materials using the Travelling Microscope. Based on the results of this study, it can be concluded that: [1] The method of activation of the tested provisional restorative materials, whether heat or chemical processing, plays the principal role in the improvement of the selected physico-mechanical properties. [2] The compositional pattern of the tested provisional restorative materials regarding the resin type and/or the incorporated filler type and loading affect dramatically their physico-mechanical behaviour. [3] The dispensing system [mixing technique] of the provisional restorative materials is a contributing factor in obtaining adequate physico-mechanical properties. [4] The water sorption process is usually associated with color change of the tested provisional restorative materials