Studies on the metabolism of 2,4'-isobutylphenylpropionic acid (ibuprofen) by gas chromatography and mass spectrometry. Dialysis fluid, a convenient medium for studies on drug metabolism.

2,4'-Isobutylphenylpropionic acid (ibuprofen) has previously been demonstrated to yield four urinary metabolites, formed by omega 1-, omega 2- and omega 3-hydroxylation and by a further oxidation of the primary alcohol of the omega 1-hydroxylated metabolite to a carboxyl group. By synthesis and gas chromatography--mass spectrometry the suggested structure of the omega 3-hydroxylated metabolite was verified in the present study. Moreover, a new metabolite, 2,4'-carboxyphenylpropionic acid, was demonstrated to be present in substantial amounts in dialysis fluid from a nephrectomized patient. In such patients ingested drugs cannot be excreted in the urine, but are metabolized to end products. Thus, dialysis fluid may be a convenient medium for studies on drug metabolism.