Penetration enhancing effect of Azone on the transport of 5-fluorouracil across the hairless rat skin

The effect of the penetration enhancer, Azone, on drug transport across skin was investigated using an in vitro permeation technique involving diffusion cells, hairless rat skin and 5-fluorouracil. The permeability of 5-fluorouracil across full-thickness skin (stratum corneum to dermis transport) was enhanced by Azone about 100-fold although a lag time of approximately 10 h was observed. This long lag time was not found after in vitro and in vivo pretreatments with Azone. Azone had no effect on the epidermis-to-dermis transport (across stripped skin) or dermis-to-stratum corneum transport (across reversed full-thickness skin). These results suggest that the amount of Azone in the skin, especially in the stratum corneum, may be related to its penetration enhancing effect. The results also suggest that incorporation of Azone into transdermal dosage forms could be useful in enhancing the transport of drugs for which the rate-limiting step for percutaneous absorption is penetration of the stratum corneum.