Duration and reversibility of the penetration-enhancing effect of azone.

In order to establish the duration and reversibility of the action of Azone, the permeation of 5-fluorouracil (5-FU) across the excised skin at 0, 1, 3 and 7 d after a 24 h pretreatment with Azone gel in hairless rats was measured. The longer the time after the pretreatment, the less Azone remained in the rat skin. The skin permeation of 5-FU was also decreased with the passage of time after the pretreatment. The amont of Azone at 7 d after the pretreatment was negligible in the skin compared to that at 0 d after the pretreatment, and the permeation rate of 5-FU across the skin at 7 d after the pretreatment was almost the same as that of the control (without Azone pretreatment). A good relationship between the remaining amount of Azone in the skin and the amount of 5-FU that permeated across the skin was observed (r=0.986). These results suggest that the penetration-enhancing effect of Azone decreases with time and is reversible.