Nimesulide-modified gum karaya solid mixtures: preparation, characterization, and formulation development.

Solid mixtures of nimesulide (NS) and modified gum karaya (MGK) were prepared to improve the dissolution rate of NS. The effect of drug-carrier ratio on dissolution rate of NS was investigated by preparing the solid mixtures of different ratios by cogrinding method. Solid mixtures were also prepared by physical mixing, kneading, and solid dispersion techniques to study the influence of method of preparation. Differential Scanning Calorimetry (DSC), X-ray Diffraction (XRD), and equilibrium solubility studies were performed to explain the results of in vitro dissolution rate studies. It was clearly evident from the results that the NS dissolution rate was dependent on the concentration of MGK in the solid mixtures, and optimum weight ratio was found to be 1:4 (NS:MGK). Though the dissolution rate of NS from all solid mixtures prepared by different methods improved significantly, maximum improvement in dissolution rate was observed with solid dispersions. The order of methods basing on their effect on dissolution efficiency is solid dispersion > kneading > cogrinding > physical mixing > pure NS. Tablets of pure drug and solid mixtures (1:4 w/w, NS:MGK) were prepared. Though the best results from the dissolution test were obtained for the tablets containing solid dispersions, tablets containing cogrinding mixture were found to be suitable, from a practical point of view, for commercialization.

Correlation of "in vitro" release and "in vivo" absorption characteristics of rifampicin from ethylcellulose coated nonpareil beads.

The purpose of this study was to investigate the possibility to develop different levels of correlation between in vitro dissolution parameters and in vivo pharmacokinetic parameters for three rifampicin formulations. A level A correlation of in vitro release and in vivo absorption could be obtained for individual plasma level data by means of the Wagner and Nelson method. Linear correlation could be obtained when percent dose released in vitro was plotted vs percent dose absorbed in vivo with correlation coefficients between 0.954,0.983 and 0.997 for the formulations studied. A second level correlation between mean in vitro dissolution time (MDT) and mean in vivo residence time (MRT) was performed with a correlation coefficient of 0.536,0.420 and 0.335. Finally, it was also possible to establish a good in vitro-in vivo correlation when the T(50%hrs) (time taken to release 50% of rifampicin) in vitro and C(max),T(max) or AUC in vivo were compared.