Abstract
The absorption of the unionized forms of barbituric acid derivatives from rat stomach was found to be a first order process and varied with the differences in the chemical structures. N-methylation and O-S displacement markedly affected the gastric absorption. The mediated physicochemical factor was partition coefficient to organic solvent. Effect of pH of drug solution also influenced the absorption of especially readily absorbed derivatives. In respect to ionized forms, the similarity in rate constants was observed among all series of derivatives, and the mechanism involved was assumed to be a physical diffusion through pores. From these observations, it was concluded that all types of barbituric acid derivatives are absorbed from rat stomach by a relatively simple physical process, which is in good agreement with pH-partition process suggested by Brodie, et al.
