Preparation and evaluation of Eudragit gels. VI: In vivo evaluation of Eudispert rectal hydrogel and xerogel containing salicylamide.

Eudispert hv hydrogel and xerogel preparations containing salicylamide displayed sustained-release plasma profiles when compared with other conventional rectal preparations. The absolute bioavailability of salicylamide was 97.3% for the hydrogel preparation and 98.4% for the xerogel preparation. These results may arise because the gel preparation stays at the application site, the lower part of the rectum, over a fairly long period because of its bioadhesive force. Furthermore, the gastrointestinal and hepatic first-pass elimination of salicylamide can be avoided completely by rectal administration of these preparations. Visual and optical microscopic observation of rectal membranes indicated no irritation or abnormality after administration of Eudispert hv hydrogel and xerogel.