Propoxyphene and norpropoxyphene: Influence of type of controlled-release formulation on intra- and intersubject variations

Two types of controlled-release formulations of propoxy-phene hydrochloride, one with a buffer system in the pellet core, were studied with regard to intra- and intersubject variations of Cmax and Tmax of propoxyphene as well as propoxyphene plus norpropoxyphene in 35 volunteers after administration of a single 150-mg dose. Statistically significant differences between the formulations in intrasubject variance were revealed, and the availability rate of the buffered product showed significantly better reproducibility, presumably due to the established low sensitivity of its release rate to the in vitro environment, i.e., pH.