Performance of human mass balance/metabolite identification studies using stable isotope (13C, 15N) labeling and continuous-flow isotope-ratio mass spectrometry as an alternative to radioactive labeling methods.
Stable isotope labeling in therapeutic and subtherapeutic quantities of drug (15N2(13)C-phenobarbital) can be quantitated in biological matrices (urine) and high performance liquid chromatography (HPLC) peaks from urine using continuous-flow isotope-ratio mass spectrometry (CF-IRMS). Standard curves for 15N2(13)C-phenobarbital were reproducible and linear (R2 > 0.985) over the ranges of 3-100 micrograms/ml for whole urine (15N2 or 13C labeling) and 0.1-8.0 micrograms/mL for HPLC peaks derived from urine (15N2 labeling). The lower limit of quantitation values for urine drug concentration was 0.46-2.62 micrograms/mL in whole urine and 0.10-0.70 micrograms/mL in HPLC peaks. Validation samples quantitated with these standard curves yielded close to expected values. These data suggest stable isotope labeling and CF-IRMS may be used as an alternative to 14C labeling and radioactivity counting methods in mass balance/metabolite identification and other biomedical studies.
Browne
T R
TR
Department of Neurology, Boston University School of Medicine, MA.
Szabo
G K
GK
Ajami
A
A
Wagner
D
D
D002247:Carbon Isotopes; D002851:Chromatography, High Pressure Liquid; D006801:Humans; D007553:Isotope Labeling / Q000379:methods*; D013058:Mass Spectrometry / Q000379:methods*; D009587:Nitrogen Isotopes; D004364:Pharmaceutical Preparations / Q000378:metabolism*; D010634:Phenobarbital / Q000378:metabolism; D010672:Phenytoin / Q000378:metabolism
D002247:Carbon Isotopes; D009587:Nitrogen Isotopes; D004364:Pharmaceutical Preparations; D010672:Phenytoin; D010634:Phenobarbital