Yoshida, Toshiko

The plasma concentration of indomethacin was measured after the rectal administration of water-soluble and fatty base suppositories in rats. The results were compared with the in vitro indomethacin release from suppositories determined by Paddle method using three different types of membranes: cellulose membrane, artificial sausage membrane and natural sausage membrane. The plasma concentrations of indomethacin during the first 4h after the rectal administration were higher in rats that received water-soluble base suppositories than in those that received fatty base types. When either a cellulose membrane or an artificial sausage membrane of cow protein was used in the Paddle method, the amount of indomethacin released from fatty base suppositories was significantly higher than that from water-soluble base ones. However, the results were reversed when a natural sausage membrane of pig colon was used. The discrepancy in the in vitro experiments using water-soluble base suppositories seemed to be due to the difference of pore size of membrane used. Careful consideration should be given to the membrane used in the Paddle method especially when this method is employed to examine the release of poorly soluble drugs like indomethacin in both water-soluble and fatty base suppositories.

The release of indomethacin from fatty-base suppositories, which had been stored at a low (4 degrees C) and a high (25-30 degrees C) temperature for about one month, was examined in vitro and in vivo. In the in vivo experiments, the plasma indomethacin levels after administration of suppositories stored at different temperatures were measured in conscious and anesthetized rats. In the in vitro release test using a dialysis cell method, much lower amounts of indomethacin were released from the suppositories stored at a high temperature than from those stored at a low temperature. The melting point of suppositories stored at a high temperature was higher by approximately 2 degrees C than those stored at a low temperature. In conscious rats, the plasma indomethacin levels attained after the intrarectal administration of suppositories stored at a high temperature were slightly lower than those after the animals were given suppositories stored at a low temperature, but the difference was significant only 30 min after administration. In anesthetized rats, the plasma indomethacin levels were markedly lower than those in conscious rats, and the influence of the storage temperature on the plasma indomethacin levels was clearly observed. These results suggest that in conscious rats many factors such as a locomotor hyperactivity and enhancement of gastrointestinal motility caused by the rectal administration mask the real character of suppositories. The in vitro and in vivo results show that the release of indomethacin from fatty-base suppositories stored at a high temperature is less than the release from those stored at a low temperature.

This study was designed to determine the in vitro release of tegafur from a suppository and the in vivo bioavailability of tegafur in rats. Two different suppository preparations (product A-1 and product A-2) containing 750 mg of tegafur were tested for in vitro release of tegafur by the Muranishi Method (membrane diffusion method) and the partially modified paddle method (permeability through dialysis tubing). When determined by either method, the amount of tegafur released from product A-2 during the whole experimental period was significantly greater than that released from product A-1. When tested by the Muranishi method, however, the difference in the amount released during the first 10-min period was not significant. A greater bioavailability of tegafur after rectal administration was obtained by product A-2 more than product A-1. A significant correlation was observed between the in vitro release and the in vivo bioavailability. The present results indicate that there are considerable differences in physiochemical characteristics between product A-1 and product A-2.