Background: Udenafil, a recently discovered drug used for erectile dysfunction treatment,
has been widely prescribed and its effect on human systems has been extensively studied.
However, there is little research on the human metabolites of udenafil. Three metabolites have
been identified in rats.
Objective: Herein, highly sensitive and accurate liquid chromatography–quadrupole time-of-flight
tandem mass spectrometry (LC-Q-TOF-MS/MS) was conducted to identify new udenafil metabolites.
Methods: Human liver microsomes were incubated with udenafil for in vitro samples, and rat
urine and faeces samples were collected from udenafil-administered rats for in vivo samples.
Each sample was deproteinated with acetonitrile and extracted by solid phase extraction. The purified
samples were separated and analyzed by LC-Q-TOF-MS, and some metabolite candidates
were reanalyzed for further structural analysis using LC-Q-TOF-MS/MS.
Results: Eleven and three metabolites were identified in the in vitro and in vivo samples, respectively,
and were found to be hydrolyzed, oxidized, or demethylated forms of udenafil or its metabolites.
The error of the metabolic analysis was −8.7 to 7.6 ppm, indicating the high accuracy of
Conclusion: These metabolic results could be useful for further investigation of udenafil and new