Determination of diclofenac and its metabolites in human urine by GC-MS

This study has been described the metabolism and excretion in a healthy male urine collected for 26hrs after oral administration of diclofenac. To detect conjugated metabolites of diclofenac, urine sample was acid-hydrolyzed under the conditions of 6M-HCl at over 110 degrees C for 1hr. During the acidic hydrolysis process, diclofenac and its metabolites were converted into their corresponding lactam-ring through dehydration reaction. As results of chemical conversion by means of hydrolysis, the structures of diclofenac and its metabolites were also changed acidic to basic forms. However, lactam-ring was degraded by hydroxyl ion at basic condition. Thus, the extraction rate of dehydrated diclofenac and its metabolites was not favored at basic condition. For the determination of trace amounts of diclofenac and its metabolites in urine, trimethylsilylation (TMS) with MSTFA was applied and followed by analysis with gas chromatograph-mass spectrometer. In this study, four metabolites that are formed by the hydroxylation of parent drug were mainly detected. Each metabolite was tentatively identified by both interpretation of mass spectra and comparison with previously reported results. In addition, time profile of urinary excretion rate for parent drugs and metabolites was studied. Finally, the metabolic pathway of diclofenac was suggested on the basis of the elucidation of its metabolites and excretion profiles.