Effect of ketoconazole on the pharmacokinetics of udenafil in healthy Korean subjects

Aims: Udenafil is a phosphodiesterase 5 inhibitor used for the treatment of erectile dysfunction. It is metabolized to DA-8164, a major metabolite, by CYP3A4. This study was performed to investigate the effect of ketoconazole, a known CYP3A4 inhibitor, on the pharmacokinetics of udenafil. Methods: An open-label, two-period, fixed-sequence crossover study was performed in 12 healthy male volunteers. They received a single 100-mg oral dose of udenafil. Following a 5-day interval, 400 mg of ketoconazole was administered once a day for three consecutive days. On day 3 of ketoconazole treatment, a second 100 mg of udenafil was dosed concomitantly. Blood samples were collected at time points up to 48 h without ketoconazole treatment and up to 72 h with ketoconazole co-administration. The plasma concentration of udenafil was determined using liquid chromatography-tandem mass spectrometry. Results: Following ketoconazole co-administration, the mean C_max and AUC_last of udenafil (95% confidence interval) increased 1.9-fold (1.60, 2.27) and 3.2-fold (2.82, 3.63), respectively. The median time to reach the C_max was delayed in the co-administrated treatment, while the mean terminal elimination half-life (t_1/2) remained relatively unchanged regardless of ketoconazole co-administration. The metabolic AUC ratio (AUC_last of DA-8164/AUC_last of udenafil) was 1.71 when udenafil was administered alone, and the value decreased to 0.19 when udenafil was dosed in the presence of ketoconazole. Regarding safety assessments, no clinically significant difference or serious adverse event was observed. Conclusions: The systemic exposure of udenafil increased significantly when it was administered with ketoconazole. Dose adjustment may be required when these drugs are used together.