THE EFFECT OF MOLECULAR VOLUME AND PARTITION COEFFICIENT ON PERCUTANEOUS ABSORPTION

A series of 8 ρ--aminobenzoate esters were selected as model drugs to study theeffect of molecular volume and partition coefficient on percutaneous absorption. The octanol/waterpartition coefficient and solubility of these compounds were determined and their penetration ratethrough rat skin in vitro was measured using a Keshany--Chien diffusion cell. The results showed thatwhen the molecular volume was increased the permeation coefficient was decreased. However, whenthe partition coefficient was increased, the permeation coefficient was increased at first and thenreached a plateau. The mathematical formula has been derived from a bi-layer diffusion model to showhow the molecular volume and the partition coefficient influence the permeation coefficient. The for-mula could be used to estimate the permeation coefficient of drug through skin.