Optimization of the in vitro release of zomepirac from suspensions and suppositories

Abstract

In an in vitro study the release rates of zomepirac acid (I) and zomepirac sodium dihydrate (II) from suspensions in liquid paraffin towards an aqueous phase were determined. When calcium was added to the aqueous phase a cake of zomepiraecalcium was formed at the interface paraffin/buffer and the release rates of I and/or II decreased extensively. The influence of additives, i.e. Tween 80, PVP and lecithin, in the suspension on this caking process was determined. It was found that Tween 80 was the most effective additive. The results obtained were ‘transformed’ to the release of II from suppositories (in vitro studies in a modified Paddle set-up). Again Tween 80 was the most effective additive; the influence of lecithin and PVP was negligible.