In situ intestinal permeability and in vivo absorption characteristics of olmesartan medoxomil in self-microemulsifying drug delivery system

To characterize the intestinal absorption behavior of olmesartan medoxomil (OLM) and to evaluate the absorption-improving potential of a self-microemulsifying drug delivery system (SMEDDS), we performed in situ single-pass intestinal perfusion (SPIP) and in vivo pharmacokinetic studies in rats. The SPIP study revealed that OLM is absorbed throughout whole intestinal regions, favoring proximal segments, at drug levels of 10-90 mu M. The greatest value for effective permeability coefficient (P-eff) was 11.4 x 10(-6) cm/s in the duodenum (90 mu M); the lowest value was 2.9 x 10(-6) cm/s in the ileum (10 mu M). A SMEDDS formulation consisting of Capryol 90, Labrasol, and Transcutol, which has a droplet size of 200 nm and self-dispersion time of 21 s, doubled upper intestinal permeability of OLM. The SMEDDS also improved oral bioavailability of OLM in vivo: a 2.7-fold increase in the area under the curve (AUC) with elevated maximum plasma concentration (C-max) and shortened peak time (T-max) compared to an OLM suspension. A strong correlation (r(2) = 0.955) was also found between the in situ jejunal P-eff and the in vivo AUC values. Our study illustrates that the SMEDDS formulation holds great potential as an alternative to increased oral absorption of OLM.