A pharmacokinetic drug-drug interaction study between selexipag and midazolam, a CYP3A4 substrate, in healthy male subjects.

Purpose: In vitro data showed that selexipag and its active metabolite (ACT-333679) have an inductive effect on CYP3A4, CYP2B6, and CYP2C9 at concentrations approximately 100-fold higher than the maximum plasma concentration (C ) measured under steady-state conditions. In order to confirm in vivo the lack of induction at the enterocyte level, we assessed the effect of selexipag on midazolam, a substrate of hepatic and intestinal CYP3A4.

Methods: This study was conducted according to an open-label, randomized, two-way crossover design. A total of 20 subjects received a single oral dose of 7.5 mg midazolam alone (treatment A) or on top of steady-state selexipag (treatment B). Selexipag was administered twice daily using an up-titration scheme consisting of three steps: 400, 600, 1000, and 1600 μg with increments every fourth day. A 24-h pharmacokinetic profile was performed following midazolam administration, and bioequivalence criteria were investigated on an exploratory basis.

Results: The C of midazolam and 1-hydroxymidazolam was decreased by approximately 20 and 14%, respectively, following treatment B compared to A. The time to reach C for midazolam and 1-hydroxymidazolam was similar between treatments. The terminal half-life was reduced in treatment B compared to A for both midazolam (16%) and 1-hydroxymidazolam (20%). Exposure (area under the curve) to midazolam and 1-hydroxymidazolam was similar between treatments, and the 90% confidence intervals of geometric mean ratios were within the bioequivalence interval. Treatment with midazolam, selexipag, and the combination was safe and well tolerated.

Conclusion: Exposure to midazolam and 1-hydroxymidazolam was not affected by treatment with selexipag.