Skin Permeation Enhancement of Drugs by Lipophilic and Hydrophilic Vehicles

The in vitro skin permeability of 16 drugs with a wide span of lipophilicity (log P ranging from -0,95 to 4.40) was evaluated with an ethanol/panasate 800 (tricaprylin, P-800) (40/60) lipophilic binary vehicle and an ethanol/water (60/40) hydrophilic binary vehicle with lauric acid, The skin permeability of the drugs was enhanced by the use of the ethanol/P-800 (40/60) binary vehicle or the ethanol/water (60/40) binary vehicle with lauric acid; permeation rate was increased and lag time' was decreased. The relationship between lipophilicity and skin permeation rate of the drugs showed parabolic shapes with their peaks at much greater hydrophilic range compared with other past references. In the in vivo skin absorption of theophylline using abdominal rat skin, the ethanol/P-800 (40/60)-7% (w/w) ethycellulose gel produced a good feature as a sustained-release preparation, and the ethanol/water (60/40)-3 % (w/w) HPMC gel with lauric acid showed the highest BA value. The results suggest that the lipophilicity of a drug is a main factor for prediction of the skin permeability of the drug and that the ethanol/P-800 (40/60) binary vehicle and ethanol/water (60/40) binary vehicle with lauric acid would be good candidates for clinical transdermal application of hydrophilic drugs.