Study design
This study was a repeated-dose, single-center, open-label, phase 1 study conducted between November 2015 and June 2016 in Japan. The study protocol and the informed consent form were approved by the Institutional Review Board of Hakata Clinic. All participants gave written informed consent before initiation of any study-specific procedures. The study was conducted in accordance with the ethical principles originating in or derived from the Declaration of Helsinki, and Good Clinical Practice guidelines.
Subjects orally received 960 mg of carotegrast methyl three times daily for 14 days from day 1 to day 14. Carotegrast methyl was administered 30 min after each meal, but under fasting conditions in the morning on the day of blood collection. A single dose of midazolam (5 mg; po, 0.017 mg kg-1; iv), prednisolone (5 mg; po), or atorvastatin (10 mg; po) was administered under fasting conditions on day -1 (one day before the start of carotegrast methyl administration), day 7 (coadministration with carotegrast methyl), day 14 (coadministration with carotegrast methyl), day 28 (14 days after the end of carotegrast methyl administration) and day 48 (28 days after the end of carotegrast methyl administration). Because the median time for intravenous midazolam to reach the maximum drug concentration (Tmax) was two hours, the drug was administered two hours after the administration of carotegrast methyl. Each coadministration cohort consisted of 20 subjects, 80 subjects in total, and the cohort to which carotegrast methyl alone was administered consisted of eight subjects. When the 90% confidence interval (CI) of the geometric mean ratio of the area under the concentration‐time curve from time of dosing to time of last measurable concentration (AUC0-t) and maximum concentration (Cmax) of oral midazolam both with and without concomitant carotegrast methyl fell within the range of 0.80 − 1.25, it was determined that there was no pharmacokinetic interaction between the drugs, subsequent combination studies were not conducted.
Midazolam was selected for this study because it is a representative substrate of CYP3A4 listed in the guideline13 and used in many clinical studies as a sensitive probe for drug-drug interactions mediated by human CYP3A4.14-16 When given orally, midazolam is quickly metabolized via the first-pass effect, which is not only associated with CYP3A4 in the liver, but also in the small intestine.17 On the other hand, intravenous midazolam, mainly metabolized in the liver by CYP3A4, is one of the most commonly used medications for inducing anxiolysis or sedation or both, prior to colonoscopy in patients with UC.18 Therefore, whether carotegrast methyl interacted with intravenous midazolam was also investigated. Prednisolone is used for inducing remission of UC19 and it is known to be a substrate of CYP3A4.20-22 Atorvastatin is a substrate of CYP3A423-25 and a typical substrate of OATP1B1/1B3.13 It has been reported26,27 that the ratio of the contribution of CYP3A4 to the oral clearance of midazolam, atorvastatin, and prednisolone is 92%, 68%, and 18%, respectively.
In order to maximize the inhibitory effect of carotegrast methyl on CYP3A4, carotegrast methyl should be administered for more than ten days because the recovery half-life of CYP3A4 activity following 14-day treatment with St. John’s Wort was reported to be 46.2 h,28 and five times its half-life is 231 h (9.6 days). Therefore, we set a 14-day treatment period for carotegrast methyl. The follow-up period was four weeks after the end of administration of carotegrast methyl. Subjects were admitted to the study center on day -3 and discharged on day 15. The second admission was from day 27 to day 42.