Enhancement of the bioavailability of cinnarizine from its .BETA.-cyclodextrin complex on oral administration with L-isoleucine as a competing agent.

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Abstract
This investigation was aimed at the improvement of the bioavailability of cinnarizine (CN) by administering its .beta.-cyclodextrin (.beta.-CD) complex together with a competing agent. The ability of L-leucine (L-Leu) and L-isoleucine (L-Ileu) to act as competing agents was evaluated by determining the penetration rate of CN, employing a Sartorius absorption simulator. L-Ileu showed a stronger competing action than L-Leu. The bioavailability of CN, upon oral administration of the CN-.beta.-CD inclusion complex, was enhanced by the simultaneous administration of L-Ileu as a competing agent; Cmax was 1.9 and 2.7 times those of CN-.beta.-CD complex alone and CN alone, respectively. L-Leu showed no clear effect on the bioavailabiity. The in vivo competing effects of L-Leu and L-Ileu appeared to be in agreement with the in vitro evaluations.