Transdermal permeability of l- and dl-norgestrel through human skin in vitro

Transdermal permeability of l-norgestrel (l-NG) and dl-norgestrel (dl-NG) at 6 skin regions with and without stratum corneum was investigated by using Valia-Chien double-compartment permeation cells. The permeation rates and accumulative amounts within 72 h in vitro were measured by HPLC. The results showed that the permeation rates of dl-NG through intact skin were significantly higher than those of l-NG (P less than 0.01). For the skins without stratum corneum, the permeation rates and permeation amounts of l-NG and dl-NG were higher than those for the intact skin (P less than 0.01), but no significant difference was seen between l-NG and dl-NG. Hence the stratum corneum played an important role of rate-limiting barrier in the skin permeation of l-NG and dl-NG. It is possible that the difference in permeability between l-NG and dl-NG is related to their partition coefficients