Absorption and Excretion of Drugs. XXX. Absorption of Barbituric Acid Derivatives from Rat Stomach.

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Abstract
The absorption of the unionized forms of barbituric acid derivatives from rat stomach was a 1st order process and varied with the differences in the chemical structures. N-methyla-tion and O-S displacement markedly affected 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. All types of barbituric acid derivatives are absorbed from rat stomach by a relatively simple physical process, which is in agreement with pH-partition process suggested by Brodie.