This study characterized the pharmacokinetic (PK) profile and evaluated the bioequivalence of sildenafil citrate under fasting conditions in Chinese subjects. A single-center, randomized, open-label, single-dose, two-sequence, two-period crossover study was conducted. Thirty-eight subjects were randomized (1:1) to the TR or RT sequence and received the test (T) and reference (R) formulations in the two study periods separated by an adequate washout. Plasma concentrations of sildenafil and N-desmethyl sildenafil were quantified using high-performance liquid chromatography-tandem mass spectrometry. PK parameters were derived by noncompartmental analysis using Phoenix WinNonlin (version 8.4), and bioequivalence was assessed based on the geometric mean ratios (GMRs; T/R) and their 90% confidence intervals (CIs) for sildenafil Cmax, AUC0-t, and AUC0-∞. All 38 subjects completed the study. Following administration of T and R, the mean ± SD Cmax of sildenafil was 319.08 ± 124.07 and 334.89 ± 189.28 ng/mL, respectively; AUC0-t was 838.10 ± 351.13 and 823.64 ± 346.63 h ng/mL; and AUC0-∞ was 872.05 ± 360.26 and 856.12 ± 357.16 h ng/mL. For N-desmethyl sildenafil, the mean ± SD Cmax was 171.97 ± 70.05 and 168.67 ± 64.07 ng/mL; AUC0-t was 708.51 ± 372.91 and 667.19 ± 315.07 h ng/mL; and AUC0-∞ was 746.10 ± 378.76 and 705.23 ± 329.39 h ng/mL, respectively. The 90% CIs for the GMRs (T/R) of sildenafil Cmax, AUC0-t, and AUC0-∞ were 92.69%-106.36%, 97.26%-106.81%, and 97.39%-106.76%, respectively, all within the predefined bioequivalence range of 80.00%-125.00%. These results demonstrate that the test and reference formulations are bioequivalent with respect to the rate and extent of absorption in Chinese subjects under fasting conditions.
Chen et al. (Sun,) studied this question.