8.5.1.3　Cyclodextrins

Cyclodextrins（CDs）are cyclic oligosaccharides whose repeating units of α-Dglucopyranose are connected to each other through carbon atoms in the α-1 and α-4 positions.The structures of CDs are shaped like a cone，with hydrophilic hydroxyl groups on the outside of the cone and lipophilic framework carbon and etheric oxygen distributed on the surface of inner cavity，in which lipophilic drugs can be carried in the inner cavity.CDs have a large molecular weight（MW=1134.98）and a low logP value（-3 to 0），so its transdermal ability is not strong.But they can bind to poorly soluble lipophilic drugs to increase their solubility and stability，thus increasing their skin permeability.However，in general，CDs do not increase the permeability of drugs across stratum corneum，which is still not easy for transdermal transport of cyclodextrin-drug complexes.Solutions to improve its transdermal efficiency include modification of lipophilic groups on the surface or combination with small molecule chemical penetration enhancers.(https://www.daowen.com)