Abstract
Comparative studies of oily vehicles, hydrocarbons (HC), esters (E), and tri-glycerides (TG), were done on percutaneous absorption of salicylic acid (SA), physicochemical parameters. and trans-epidermal water loss(TEWL) in rat. The diffusion concept was supported experimentally ; vehicle viscosity was found to be an important restriction factor of drug absorption. In HC, which had low affinity to SA as estimated by solubility and partition coefficient, good correlation was obtained between drug absorption and viscotity, but this correlation could be seen only within the series. In spite of using the same series, the reverse effect was obtained in the lower molecular weight range of TG ; absorption decreased according to increase in affinity to SA, and maximum absorption appeared with the medium-chain length TG. In E, the skin-altering effect may have a rather important role in absorption, although the viscosity effect was seen. TEWL was suppressed by HC, promoted by E. and promoted slightly by TG. TEWL values correlated well with SA absorption suggesting the importance of the physiological effect of the vehicle in drug absorption.
