Studies on Absorption and Excretion of Drugs. I. Kinetics of Penetration of Acidic Drug, Salicylic Acid, through the Intestinal Barrier in vitro.

Abstract

1. A penetration of salicylic acid through the rat small intestine was investigated from the standpoint of chemical kinetics in vitro. 2. Theoretical equations were derived from the assumption that the intestinal barrier was partially permeable to both the undissociated and dissociated forms of the drug. 3. From the data obtained, the respective permeability coefficients for the undissociated and dissociated forms of salicylic acid, Pu and Pi, were statistically determined. The estimated value of Pu was 0.0125 (cc./cm./min.) and that of Pi 0.00233 (cc./cm./min.). 4. As there was a little difference between the observed and the calculated values, an experiment at the equilibrium state was tried for the purpose of elucidating the cause of the difference. 5. The results indicate that salicylic acid is transferred across the intestinal barrier with specific coefficient for both forms of drug, Pu and Pi, that the ratio for Pu/Pi is about 6, and the relative rapid penetration of the dissociated form can be attributed to the above ratio.