Pharmaceutical studies of polyacrylic acid aqueous gel bases. II. Absorption of ibuprofen from gel preparations following rectal administration in rats.

Ibuprofen (IP) gel preparations made by suspending IP in a polyacrylic acid aqueous gel were administered rectally to rats by an in situ rectal loop method, and the IP plasma levels were determined. In addition, the IP release rate from gel preparations was examined in vitro and the correlation with the in situ data was investigated. In the case of IP gel preparations with a higher viscosity or a lower pH, IP plasma levels were maintained for a longer period and the IP release rate from the gel preparation was small. IP plasma levels reached their peaks between one and two hours. The AUC by rectal administration was not influenced by the viscosity or pH of the gel preparation and was about twice the AUC by oral administration. Thus, it appears that aqueous polyacrylic acid gels are useful as a base for rectal drug administration ; the duration of high IP plasma level can be controlled by changing the viscosity and pH.