K. Akira et al., Direct nuclear magnetic resonance spectroscopic analysis of C-13-labeled antipyrine metabolites in human urine, DRUG META D, 29(6), 2001, pp. 903-907
Antipyrine is a useful probe to evaluate variation of in vivo activities of
oxidative hepatic drug-metabolizing enzymes. Here we describe an approach
using C-13 labeling and NMR spectroscopy for the direct and simultaneous an
alysis of major metabolites of antipyrine in human urine. [C-Methyl-C-13]an
tipyrine (500 mg) was dosed orally to human volunteers, and the post-dose u
rine was analyzed by 100-MHz C-13 NMR spectroscopy under the conditions of
distortionless enhancement by polarization transfer (DEPT) without any pret
reatments such as deconjugation, chromatographic separation, or solvent ext
raction. Consequently, all the major metabolites in urine were successfully
detected with favorable signal-to-noise ratios in the limited acquisition
time (30 min). The reproducibility of the NMR detection was sufficient for
the quantitative evaluation of the metabolic profile. A quantitative method
is proposed using a combination of inverse gated decoupling and DEFT exper
iments with [2-C-13]sodium acetate as an internal standard. The present app
roach is useful and practical to evaluate variation of in vivo activities o
f the conjugation enzymes as well as oxidative enzymes responsible for the
formation of antipyrine metabolites in humans. This direct approach would e
nhance the value of the antipyrine test because of its simplicity and conve
nience.