A Novel Prodrug of Salicylic Acid, Salicylic Acid-Glutamic Acid Conjugate Utilizing Hydrolysis in Rabbit Intestinal Microorganisms.

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Abstract
The fate of salicylic acid-glutamic acid conjugate (salicyl-glutamic acid) following oral, intravenous, intracecal and rectal administration (60, 10, 5 and 5 mg/kg, respectively: salicylic acid equivalent) was examined in rabbits. Salicylic acid was detected in the blood 2 h after oral administration of salicyl-glutamic acid and it reached the maximum level (69.4 micrograms/ml) at 18 h after the dose. A high blood concentration of salicylic acid (24.8 micrograms/ml) was observed up to 36 h. But only a small amount of salicyl-glutamic acid was detected in the blood (less than 2.5 micrograms/ml, as salicylic acid). In contrast, unchanged salicyl-glutamic acid was found mainly in the blood following intravenous administration of salicyl-glutamic acid, suggesting that presystemic de-conjugation of salicyl-glutamic acid predominantly occurred. The intestinal mucosal de-conjugation of salicyl-glutamic acid was negligible in the in situ intestinal sac preparation with complete mesenteric venous blood collection. Immediate and very extensive salicylic acid formation in the cecum was found following intracecal administration of salicyl-glutamic acid. After oral pretreatment of rabbits with kanamycin sulfate (6 x 400 mg), a significant inhibition of salicylic acid formation following intracecal administration of salicyl-glutamic acid was observed, indicating that the intestinal microorganisms were responsible for the biotransformation of salicyl-glutamic acid. Also, in vitro incubation of salicyl-glutamic acid with gut contents showed that the primary location of hydrolysis was the hind gut.

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