Influence of layer position on in vitro and in vivo release of levodopa methyl ester and carbidopa from three-layer matrix tablets.

A versatile oral controlled release system for the simultaneous delivery of levodopa methyl ester and carbidopa, consisting of a three-layer matrix tablet, has been studied and developed. Each individual layer of the matrix exhibited a different release mechanism, i.e. the first layer was swellable (S), the second one was erodible (E) and the third one was disintegrating (D). The three layers have been assembled in the monolithic matrix in different relative positions. It was found that in the monolith the three layers could interact, producing in vitro release profiles depending on their relative position. The monoliths having the configurations DSE and SDE were administered to human volunteers in order to determine the plasma profiles. The pharmacokinetic data showed a significant difference between the early time plasma curves: the monolith DSE, having the fast release profile, gave rise to a rapid appearance of a high levodopa plasma level, whereas the slower releasing monolith SDE produced a smoothed plasma concentration profile.