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

ABSTRACT

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 4.51, 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