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The anti-inflammatory, analgesic and antipyretic effects and the tolerability of 2-(4-isobutylphenyl)-propionic acid (ibuprofen) were compared with those of its derivative 2-(4-isobutylphenyl)-propiohydroxamic acid (ibuproxam, Ibudros. Our experiments show that the interfering action of the two drugs with the reactive processes of the tibio-tarsic articulation, brought about by carrageenin, serotonin, dextrane and formalin is of the same intensity. Also, the analgesic activity is perfectly consistent with the antipyretic one. However, the tolerability of the two molecules is different; the acute toxicity is consistent in the case of the single parenteral administration and it differs in the case of a single or repeated oral treatment. When used under these conditions, ibuproxam is considerably less damaging to the gastroenteric tube than is ibuprofen. The hypothesis is put forth that the greater tolerability of ibuproxam is due to its pharmacokinetics: it is, as such, little or not toxic for the mucous membrane of the digestive apparatus, and it progressively releases ibuprofen, whose concentrations in the blood would remain below those levels that cause systemic lesions in the gastroenteric tract.

The metabolism of 2-(4-isobutylphenyl)-propio-hydroxamic acid (ibuproxam, Ibudros), a new molecule with anti-inflammatory, antipyretic and analgesic activity was studied by its administration orally and rectally to the rat. The analysis, carried out with gas chromatographic method and thin-layer chromatography, showed that the drug is present in blood as 2-(4-isobutylphenyl)-propionic acid (ibuprofen), an anti-inflammatory drug which is commonly used and the metabolites of which are already known. Using the same methods, it was observed that only a few traces of the hydroxamic acid appear in the urines of rats treated with ibuproxam, whilst the ibuprofen metabolite is absent. Therefore, we conclude that the drug ibuproxam changes rapidly into ibuprofen, following afterwards the same known metabolic process as the latter drug.