The abuse of
sildenafil and its analogous, accelerated by their inappropriate or illegal distribution, is a serious social issue globally. However, no studies have been conducted to monitor these drugs simultaneously in hair, which can provide valuable information on chronic
drug use. In the present study, an LC-MS/MS method was developed for the simultaneous determination in hair of five
erectile dysfunction drugs having a high risk for abuse (
mirodenafil,
sildenafil,
tadalafil,
udenafil and
vardenafil) and their selected metabolites (
SK3541,
desmethylsildenafil, DA8164 and desethylvardenafil). The novel method was fully validated after optimizing matrix effects and extraction efficiency. The optimized sample preparation included acidic
methanol extraction followed by solid phase extraction using C18 mixed mode strong
cation exchange polymeric cartridges. The prepared samples were analyzed by LC-MS/MS with electrospray ion source in the positive ionization mode. The validation results proved the method to be selective, sensitive, accurate and precise, with acceptable linearity within calibration ranges. LODs ranged from 0.05 (DA8164) to 1 ng/10 mg hair (
tadalafil). LOQs were 1 ng/10 mg hair except for DA8164 and
vardenafil, of which they were 2.5 ng/10 mg hair. No significant variations were observed by different sources of matrices in both human and rat hair, except for
tadalafil, for which a stable
isotope-labeled internal standard was effective. The animal study suggested hair pigmentation was a major factor for the incorporation of the drugs and metabolites into hair. However, a wide variation of the
sildenafil-to-
desmethylsildenafil ratios was observed in human hair samples. The developed method will be very useful for monitoring the abuse of
erectile dysfunction drugs for both legal and public health aspects.