Simultaneous analysis of sildenafil, vardenafil, tadalafil, and their desalkyl metabolites in human whole blood and urine by isotope dilution LC–MS–MS

Abstract

Given that there are many autopsy cases in which erectile dysfunction (ED) treatment drugs can be detected from elderly men who are diagnosed to have died of cardiovascular disorders, the degree of cardiovascular risk posed by ED treatment drugs is still controversial. Moreover, counterfeit ED drugs or illegal dietary supplements containing ED drugs are also threats to public health. In this study, we established a detailed procedure for simultaneous analysis of typical ED drugs (sildenafil, vardenafil, tadalafil) and their metabolites in human blood and urine by isotope dilution liquid chromatography-tandem mass spectrometry (LC–MS–MS). Each sample of whole blood and urine containing the three ED treatment drugs, their metabolites, and deuterated internal standards (ISs) was diluted with alkalinized water, loaded onto an Oasis HLB cartridge, washed with dilute ammonium hydroxide solution, and eluted with chloroform. The eluate was acidified with methanol and concentrated HCl and evaporated to dryness. The resulting residue was reconstituted with methanol and mobile phase solution, and 5 μl of the solution was injected into an LC–MS–MS instrument. The determinations were made by multiple reaction monitoring using each product ion. The recovery rates of the drugs, metabolites, and ISs from whole blood and urine ranged from 80.7 to 127%. Good linearity was obtained for all drugs and their metabolites in the range of 1–100 ng/ml in whole blood and urine with correlation coefficients greater than 0.99. The detection limits (signal-to-noise ratio = 3) for all compounds were not higher than 0.05 ng/ml. Intraday and interday accuracy and precision data were also satisfactory for all compounds in whole blood and urine. Actual measurements of sildenafil and N-desmethyl sildenafil were also demonstrated by analysis of whole blood and urine specimens from two male volunteers after ingestion of a 25-mg tablet of sildenafil.