APPLICATION OF PACKED CAPILLARY LIQUID-CHROMATOGRAPHY MASS-SPECTROMETRY WITH ELECTROSPRAY-IONIZATION TO THE STUDY OF THE HUMAN BIOTRANSFORMATION OF THE ANTIEMETIC DRUG DOLASETRON

Packed capillary liquid chromatography/mass spectrometry (LC/MS) using electrospray ionization (ESI) was used to study the human biotransfor mation of the anti-emetic drug dolasetron, Urine from subjects given a single 100 mg intravenous dose, containing C-14-labeled dolasetron (5 0 mu Ci), was de-salted and concentrated for LC/MS with minimal loss o f radioactivity (97% recovery), Aliquots of the de-salted material wer e injected directly onto a C-8 packed capillary column (25 cm x 0.32 m m i.d.) and eluted with an acetonitrile-water gradient, buffered with 1% acetic acid, at a flow rate of 2 mu l min(-1), Five metabolites wer e detected by LC ESI-MS which, yielded molecular mass information but no fragmentation, The identity of each metabolite was confirmed in a s ubsequent analysis using product ion scans in conjunction with collisi onally induced dissociation, Precursor ion scanning was also employed and did not reveal any new biotransformation products, In addition to defining the major routes of biotransformation, the data obtained were compared with a C-14 radioprofile prepared in a separate experiment, Qualitative agreement in the two chromatographic profiles enabled the major clusters of radioactivity to be assigned to specific metabolites of dolasetron. An important observation in this comparison was that t he signal obtained by ESI did not provide an accurate assessment of th e quantity of each metabolite, This was especially true for acidic con jugates (i.e. glucuronides, sulfates), which in the case of dolasetron can exist as zwitterions (no net charge). The results demonstrate the power of packed capillary LC ESI-MS for use in drug biotransformation studies and suggest that caution should be exercised when interpretin g relative metabolite abundances from ESI data in the absence of actua l reference standards.