Synchronized release of sulpiride and sodium decanoate from HPMC matrices: A rational approach to enhance sulpiride absorption in the rat intestine

Purpose. (a) To improve the absorption of sulpiride (SP) through the intestinal wall by incorporating it together with sodium decanoate (SD) into erodible matrices, designed to synchronize the release of SP and SD over different periods of time; (b) to test, in vivo the hypothesis that this simultaneous release increases SP absorption from the intestinal lumen. Methods. Matrix tablets, possessing different erosion rates, were prepared by changing the ratios between SD and hydroxypropyl methylcellulose (HPMC). The amounts of HPMC varied from 2.5% to 17% w/w. Double layer tablets, containing similar amounts of SP, SD, and HPMC were used as nonsynchronous controls. The erosion kinetics of the tablets was assessed gravimetrically in vitro in USP basket dissolution apparatus and in vivo in the intestine of the anesthetized rat after intra-intestinal administration. SP absorption was studied after intra-intestinal administration of the different kinds of tablets to anesthetized rats, by monitoring SP blood levels. SP and SD levels in the withdrawn samples from the dissolution systems and blood were analyzed by HPLC. Results. The controlled erosion of the tablets resulted in equal release rates of SP and SD during the initial linear phase of the process. This synchronized release lasted over different time periods depending on the relative amount of HPMC in the formulations (from 1 hour to 4 hours for 2.5 and 17 % w/w of HPMC, respectively). The synchronous matrices increased SP bioavailability after intra-intestinal administration. The increase varied from 1.4 to 2.3-fold for the slow and the fast release formulations, respectively (compared with the nonsynchronous, SD containing control formulations), indicating the ability to control both erosion rate and length of intestinal segment in which absorption is taking place. Conclusions. SP bioavailability after intestinal administration can be improved only if SP is released together with SD along the entire intestinal route. This can be accomplished by the design of synchronous matrices capable of concomitant release of SP and SD despite the differences in their water solubility. The ability to manipulate and control the duration of the synchronous phase of the matrices makes it possible for SP to be absorbed at different parts of the intestine.