The Mechanism of the Secretion of Sulfonamide Drugs in Gastric Juice *

Cooke, Davenport, and Goodman4 have shown that five sulfonamide drugs are secreted in the gastric juice. When the concentration ratio is defined as the concentration in the gastric juice divided by the concentration in the plasma it is found that the average concentration ratios of sulfanilamide and sulfapyridine are 2.6 and 3.2 respectively. The average concentration ratios of sulfathiazole, sulfadiazine, and acetylsulfanilamide are 0.16, 0.28, and 0.30 respectively. The concentration ratios of all the drugs decrease significantly with increasing rates of gastric secretion, and the concentration ratios of all but sulfathiazole increase significantly with increasing plasma concentration of the drugs. The fact that the concentration ratios of sulfanilamide and sulfapyridine are greater than one makes it appear that osmotic work is done by the gastric mucosa in secreting the drugs. This cannot be explained by the tentative theory of the mechanism of acid secretion proposed by Davenport' or by any other current theory. The meaning of the variations of the concentration ratios with rate of secretion and plasma concentration is also obscure, and it must be explained before any theory of the mechanism of secretion can be accepted. This paper presents a simple and comprehensive explanation of all the observed facts of sulfonamide secretion, and it shows that the facts are not opposed to Davenport's theory of the mechanism of acid secretion. The equation for evaluating the work done when N mols of a solute are transferred from one solution where its activity is fp [PI to another in which its activity is fgj [GJ] can be written