Safety and Pharmacokinetic Studies of Silodosin, a New .Alpha.1a-Adrenoceptor Selective Antagonist, in Healthy Chinese Male Subjects

The objectives of the study were to assess the safety and pharmacokinetics of silodosin capsules in 82 healthy male Chinese subjects. To evaluate the safety after single-dosing escalation, 40 subjects were equally divided into 4 groups (2, 4, 8, 12 mg) by a randomized, double-blind and placebo-controlled design. To assess the pharmacokinetics after single-dosing, 30 subjects were equally divided into 3 groups (4, 8, 12 mg). To assess the safety and pharmacokinetics via multiple-dosing, 12 subjects were included as a group (4 mg once daily at day 1 and day 7; 4 mg twice daily at day 2 through day 6). The safety observations showed that mild adverse events, including postural hypotension, dizziness, and headache, were observed. After single-dosing at doses of 4, 8, and 12 mg, the mean area under the concentration-time curve from 0 to 36 h (AUC(0-36)) values were 136.82±46.38, 270.17±54.66, and 474.63±108.50 µg/l·h and the mean maximal silodosin concentration in plasma (C(max)) values were 26.70±7.48, 48.47±12.35, and 94.07±22.59 µg/l, respectively. After multiple-dosing, the C(max) value at day 7 was 33.84±19.54 µg/l, and the AUC(0-24) value at day 7 was 193.19±68.96 µg/l·h. The accumulation ratio of the AUC value was 1.55 by comparing the multiple-dosing with the single-dosing. It is concluded that silodosin is safe and tolerated in healthy Chinese male subjects at the dosing levels used in this study. The mean C(max) and AUC values of silodosin increased proportionally with dose escalation, showing characteristics of linear pharmacokinetics.