B Sreenivasa Rao

Studies on rifampicin release from ethylcellulose coated nonpareil beads

The rifampicin release studies from ethylcellulose coated nonpareil beads were studied. Propylene glycol and Castor oil were used as plasticizers. The in vitro dissolution studies revealed that the release rate is inversely proportional to percent of coating thickness. The release rate also depends on the type of plasticizer used in the coating polymer. The mechanism of drug release follows Higuchi diffusion model. Water vapour permeation studies indicated that the water vapour transport rate through free films is directly related to the drug release rate. DSC thermograms and IR spectras revealed that there is no interaction between rifampicin and other additives. SEM photographs of coated beads, before dissolution and after dissolution, also indicates that the drug release mechanism follows diffusion model.

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.

Preparation and In Vitro Evaluation of Chitosan Matrices Cross-Linked by Formaldehyde Vapors

Rifampicin-chitosan matrices were prepared by a chemical cross-linking method to develop a sustained-release form. The effects of cross-linking agent (formaldehyde) on the drug release rate and release kinetics were investigated in this study. Moreover, the kinetics of rifampicin released from chitosan matrices exposed to formaldehyde vapors for predetermined time intervals were analyzed using Ritger and Peppas exponential equation. The in vitro release kinetics exhibited a non-Fickian transport model. Increasing the exposure time to formaldehyde vapors decreased the release rate of rifampicin from chitosan matrices as a result of formation of greater structural strength and tighter texture.

Studies on enhancement of dissolution rate of etoposide

Dissolution is the rate-limiting step in the absorption of drugs from solid dosage forms. This is to be focused especially when the drug is poorly soluble. Etoposide is a poorly soluble drug and its absorption is dissolution rate limited. The present study is aimed at improving the dissolution of etoposide. Solid dispersions of drug with surfactants were prepared by using kneading technique. Kneading technique is more applicable to industry. Surfactants such as cetrimide, sodium lauryl sulphate, Tween 80 and Cremophor RH40 were used in different proportions. Etoposide gave faster dissolution rates when Cremophor RH40 was used. The DSC thermograms and IR spectra revealed no interaction of etoposide with these surfactants and no degradation in etoposide molecule was observed.