Age-related Pharmacokinetics Differences Were Observed Between Young and Elderly Populations of a Novel PDE5 Inhibitor, Youkenafil, and its Metabolite M459

Youkenafil is a novel oral selective PDE5 inhibitor for treating Erectile Dysfunction. This investigation assessed pharmacokinetics (PK), safety, and tolerability of youkenafil and its main metabolite (M459) after taking 100 mg youkenafil hydrochloride tablets in elderly and young subjects.This Phase I, single-center, open-label, parallel-group, single-dose study was conducted on 24 individuals (12 elders and 12 youngsters). Each subject received a single oral 100 mg youkenafil hydrochloride tablets. Blood samples were collected before medication and up to 48 h after medication for PK analysis. Safety and tolerability were also assessed, including treatment-emergent adverse events (TEAEs), laboratory tests, 12-lead ECG, vital sign inspections, color vision examinations, and physical examinations.Plasma concentrations of youkenafil and M459 were quantified. PK parameters were determined by non-compartmental analysis. Median Tmax of elderly and young groups were both 0.733 h. However, Cmax, AUC0-t, and AUC0-∞ of youkenafil were separately 16.8 %, 37.2 %, and 37.5 % higher in elders and t1/2 of youkenafil was 2.1 h longer in elders. More great differences were observed for M459. T1/2 values were 4.05 h longer in elders, with Cmax, AUC0-t and AUC0-∞ 73.7 %, 81.1 %, and 81.4 % higher in elders. Two (8.3 %) elderly subjects reported TEAEs (all grade Ⅰ in severity) and both recovered without any treatment. No serious adverse reactions (SAEs) or serious unexpected suspected adverse reactions (SUSARs) occurred in this study.This was the first PK research of youkenafil and M459 in elderly men. PK parameters differences between youkenafil and M459 were comparable between elderly and young groups. Moreover, safety and tolerability of youkenafil were favorable in both groups.