(R)-(-)-benoxaprofen is stereospecifically inverted to the (S)-(+)-enantiomer by rats and humans. The rate of inversion is much faster in rats (t 1/2 ca. 2.5 h) than in humans (t 1/2 108 h). Inversion in rats apparently does not occur in the liver, but can be brought about in vitro by an everted intestinal sac preparation, suggesting that the transformation takes place while passing through the gut wall.

1. The absorption, metabolism and excretion of isamoxole, (2-methyl-N-butyl-N-(4-methyloxazol-2-yl)propanamide), a compound with anti-allergy properties, has been studied in the rat and guinea-pig. 2. The compound was well-absorbed by both species after oral doses of 50 to 150 mg/kg. It underwent extensive first-pass metabolism in the liver, and was excreted as a mixture of metabolites, predominantly in the urine, within 48 h. 3. Three major routes of metabolism were involved, namely deacylation, oxidative ring scission and alkyl oxidation. 4. A major plasma and urine metabolite was 1-butyl-3-(1-carboxyethyl)urea, and this was accompanied by low levels of its cyclized product 3-butyl-5-methylhydantoin.

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