Data analysis and statistical analysis
The sample size was calculated using the coefficient of variations (AUC: 43.7% and Cmax: 46.8%) derived from the Cmax and AUC of carotegrast after oral administration of carotegrast methyl.17 The correlation coefficient was assumed to be 0.7. When the point estimate of the geometric mean ratio of the PK parameters of carotegrast methyl obtained in the absence and presence of rifampicin was set to 1, indicating no drug interaction, the number of subjects required to have a 90% confidence interval (CI) of 0.8 – 1.25 was calculated to be 19 for AUC and 21 for Cmax with 80% power. Considering the feasibility of conducting the trial at the study site, the number of subjects was set to 20.
The PK parameters were assessed in all subjects who received carotegrast methyl and whose PK data were adequate for the calculation of ≥ 1 primary PK parameter (the PK analysis set). Safety was assessed in all subjects who received the study drug (the safety analysis set). Levels of analyte below the level of quantification were entered as 0 for calculations. Descriptive statistics were used to summarize demographics and safety parameters. The PK parameters of carotegrast methyl, carotegrast, M-I, M-II, and carotegrast-gluc were calculated based on the plasma drug concentration data from subjects who received carotegrast methyl alone or in combination with rifampicin using non-compartmental analysis. For plasma drug concentration and PK parameters, descriptive statistics and the two-sided 95% CIs were calculated. A natural logarithmic transformation of PK parameters except for Tmax was applied for all statistical inference. The 90% CI for ratios of geometric means of logarithmic PK parameters was calculated by the following mixed effects model;
Loge (PK Parameter) = μ + group + sequence + time point + subject + ε
μ: population mean, time point: duration of administration, subject: interindividual variation, ε: error
The geometric mean ratios and their 90% CI for the AUC0-t and Cmax of carotegrast methyl and carotegrast when carotegrast methyl was administered in combination with rifampicin versus when carotegrast methyl was administered alone were calculated. When the 90% CI of the geometric mean ratio of both parameters fell within the range of 0.80 – 1.25, it was determined that there was no PK interaction. The same analysis was performed for the other metabolites including M-I, M-II and carotegrast-gluc and for other PK parameters including Tmax, t1/2, and MRT0-t as a reference. For Tmax, a nonparametric test was performed. PK parameters were calculated using noncompartmental analysis with WinNonlin Professional Version 6.3 (Phoenix Corporation, Mountain View, California, USA). AEs were coded using the Medical Dictionary for Regulatory Activities (MedDRA) version 20.0. All data processing, summarization, and analyses were conducted using SAS software ver. 9.3 for Windows (SAS Institute Inc., Cary, NC, USA).