Percutaneous absorption of alkanoic acids I: A study of operational conditions.

The rate of penetration of propionic and butyric acids through excised porcine skin was determined in vitro in specific apparatus allowing optimal control of operational conditions. In one technique, the rate was followed by continuous pH-stat titration of acid appearing in the perfusate, in another, by periodic monitoring of [14C]propionic acid in the perfusate. With the assumption that Fick's equation applies to the process of penetration, it was found that the permeability coefficient, Kp, increases with increasing mass of neat penetrant applied per unit area to the donor side, increases with increasing concentration of penetrant in n-heptane as vehicle, increases with increasing temperature, Ea = 11.4 kcal/mol, and decreases with decreasing perfusion rate of the acceptor side when this rate is smaller than 60 mL/h.