APPLICATION OF AN OILY GEL FORMED BY HYDROGENATED SOYBEAN PHOSPHOLIPIDS AS A PERCUTANEOUS ABSORPTION-TYPE OINTMENT BASE

We investigated the possibility of developing an oily gel formed by hy drogenated soybean phospholipids (HSL) as a percutaneous absorption-ty pe ointment base. Liquid paraffin (LP) was used as the oil, and indome thacin (IM), ketoprofen (KP), flurbiprofen (FP) and ibuprofen (IP) wer e used as model drugs. IM did not dissolve in LP, but solubilized when heated with HSL at a concentration of about 1% with 15% HSL at 95-deg rees-C. IM gel was thus prepared as follows: IM and HSL were mixed, ad ded into LP, capped tightly, heated in a water bath and cooled. The co nsistency of the gel increased with increasing IM concentration, indic ating some kind of interaction between IM and HSL. The release of IM f rom the IM gel was faster than that from a preparation in which IM was mixed in gel at room temperature (Gel + IM). The release rate of IM f rom IM gel was proportional to IM concentrations up to 1%, but became constant above that. Permeation of IM through hairless rat abdominal s kin from IM gel was higher than that from the Gel + IM. The permeation rate was proportional to IM concentrations in the range of 0.1 to 0.5 % in 15% HSL gel. KP and FP also solubilized in gel when subjected to the same procedure as IM, and their release and permeation increased w hen they were formulated as gels. However, no evident improvement of p ermeation was observed in the case of IP, which had high LP solubility . It was suggested that HSL showed no enhancing effect, but solubilize d IM, KP or FP, leading to high permeation from the gel. After 3 month s' storage, the permeation rate did not change for 0.5% IM in 15% HSL gel, but decreased for 1% IM in 15% HSL gel. This indicates that in th e case of 1% IM in 15% HSL gel, IM is in a supersaturated state immedi ately after preparation and then recrystallizes with time.