This study showed that the test and reference products met the regulatory criteria for bioequivalence following a 40 mg oral dose under fasting conditions.

One of the major concerns for all in vivo experiments is intra- and inter-subject variability, which can be a great source of inaccuracy. The aim of this study is, therefore, to estimate the ability of parallel vs. cross-over design studies in order to describe the relative pharmacokinetic performance of the studied drug formulations. We analyzed the data from a drug development program that examined the performance of innovative abiraterone acetate formulations against the identical reference product in three stages. In stages 1–3, groups A–F were dosed with the reference product once in a parallel manner. Stage 4 was performed to evaluate the intra-individual variability (IIV) by repeated administration of the reference product to the same animals. Although the geometric mean (90% CI) values of abiraterone AUClast in groups A–F were similar to the IIV group (24.36 (23.79–41.00) vs. 26.29 (20.56–47.00) mg/mL·min·g), the results generated in the isolated parallel groups provided imprecise estimates of the true AUClast values ranging from 9.62 to 44.62 mg/mL·min·g due to chance. Notably, in 4 out of 15 possible pair comparisons between the parallel groups, the confidence intervals did not include 100%, which is the true ratio for all comparisons tested after identical formulation administration to all groups. A cross-over design can significantly improve the methodology in short-term comparative pre-clinical pharmacokinetic studies, and can provide more precise and accurate results in comparison to more traditional pre-clinical study designs.

In this open-label, laboratory-blinded, 2-way single dose study in 24 volunteers of both sexes we found that (1) nabumetone reaches mean Cmax ± SD of 0.56 ± 0.20 mg·L at mean tmax of 8.63 ± 7.05 hours, and mean area under the curve (AUC)last of 18.07 ± 7.19 h·mg·L; (2) there are no statistically significant differences between both sexes in pharmacokinetics of nabumetone; (3) 6-methoxy-2-naphthylacetic acid (6-MNA) reaches higher AUClast in men compared with women (mean ± SD, 721.23 ± 185.53 h·mg·L and 545.27 ± 97.69 h·mg·L, respectively; P = 0.013); (4) there is lower 6-MNA clearance in men (0.65 ± 0.22 L·h) in comparison with women (0.88 ± 0.18 L·h, P = 0.019), (5) intersubject variability of nabumetone and 6-MNA is between 35%-45% and 10%-30% for all assessed pharmacokinetics parameters (AUClast, Cmax, partial AUC values); (6) intrasubject variability (ISCV) for AUClast is low, 15.59% and 6.40% for nabumetone and 6-MNA, respectively, (7) ISCV for Cmax is 13.66% and 5.42% for nabumetone and 6-MNA, respectively. Nabumetone thus belongs to compounds with low to moderate ISCV and therefore this product is expected to produce consistent effects in clinical practice.