pH-independent controlled release tablets comprising weakly acidic drug: design and evaluation

In this study, tablets were prepared by compressing mixtures of indomethacin [model drug], PVP and tromethamine [as an alkalinizer] in order to attain independent release pattern. The tablets were coated with 5% ethyl cellulose in ethyl acetate on the lateral site leaving two surfaces free or coated at all surfaces, except one. When the composition of tromethamine to the drug in the mixture was equal to or more than 4.5:1, the tablets showed pH-independent release. Release rate was controlled with tromethamine/drug ratio, the percent and type of PVP and the surface area available for drug release. Release rate can be altered freely, while maintaining the pH-independent release characteristics by combining the different composition matrices. The study showed that the best model to describe indomethacin release kinetics is mixed zero-order and Higuchi linear square root of time relationships with lag time

Potential and mechanism of A-Tab as a controlled release agent

This study investigated the mechanism by which anhydrous calcium phosphate [A-TAB] exhibits its sustained release matrix, via premixing of A-TAB [diluent] powder with different excipients, e.g. Avicel, sodium alginate and polyvinyl alcohol [PVA], to block entrapment sites if any, on the dissolution of theophylline from A-TAB tablets. Furthermore, the inclusion of other excipient [palmetic acid] to impart a more acid resistant character on the diluent/drug blend and thus assist in maintaining the matrix structure of A-TAB were also investigated. The rate and extent of drug dissolution were dependent on the order of mixing of A-TAB with the drug and excipient as well as the pH of the dissolution medium