An open‐label study to explore the optimal design of CYP3A drug–drug interaction clinical trials in healthy Chinese people

Abstract

AbstractA drug–drug interaction (DDI) trial of cytochrome P450 3A (CYP3A) is a necessary part of early‐phase trials of drugs mainly metabolized by this enzyme, but CYP3A DDI clinical trials do not have a standard design, especially for Chinese people. We aimed to offer specific recommendations for CYP3A DDI clinical trial design. This was an open, three‐cycle, self‐controlled study. Healthy subjects were given different administration strategies of CYP3A4 perpetrators. In each cycle, blood samples were collected before and within 24 h after the administration of midazolam, the CYP3A indicator substrate. The plasma concentrations of midazolam and 1‐hydroxymidazolam was obtained using liquid chromatography tandem mass spectrometry assay. For CYP3A inhibition, itraconazole exposure with a loading dose could increase the exposure of midazolam by 3.21‐fold based on maximum plasma concentration (Cmax), 8.37‐fold based on area under the curve Pharmacology Research & Perspectives for review only from zero to the time point (AUC0–t), and 11.22‐fold based on area under the curve from zero to infinity (AUC0–∞). The data were similar for itraconazole pretreatment without a loading dose. For CYP3A induction, the exposure of rifampin for 7 days decreased the plasma concentration of midazolam ~0.27‐fold based on Cmax, ~0.18‐fold based on AUC0–t, and ~0.18‐fold based on AUC0–∞. Midazolam exposure did not significantly change when the pretreatment of rifampin increased to 14 days. This study showed that itraconazole pretreatment for 3 days without a loading dose was enough for CYP3A inhibition, and pretreatment with rifampin for 7 days could induce near‐maximal CYP3A levels.