Background: A subset of patients with constipation has reduced colonic bile acid concentrations, which are associated with slow colonic transit. In a previous study, elobixibat, a locally acting ileal bile acid transporter inhibitor, accelerated colonic transit in Japanese patients with functional constipation. In this study, we aimed to determine the efficacy of elobixibat for short-term treatment of chronic constipation, and safety, patient satisfaction, and quality of life with long-term treatment. Methods: We did two phase 3 studies of patients aged 20–80 years in Japan with at least 6 months of chronic constipation, who satisfied Rome III criteria for functional constipation, including fewer than three spontaneous bowel movements per week. The first trial, including patients enrolled at 16 clinics, was a 2-week, randomised, double-blind, placebo-controlled study in which (after a 2-week run-in period) patients were randomly assigned (1:1) to either elobixibat 10 mg/day for 2 weeks or placebo. Randomisation was done with permuted block method (block size six) without stratification. Masking to treatment allocation was achieved with identical appearances of elobixibat and placebo, which were supplied in sealed, opaque containers. Group assignment was concealed from patients, investigators, and analysts. The second trial, including patients enrolled at 34 clinics or hospitals, was an open-label, 1-year study in which all patients received elobixibat; participants could titrate the dose to 5 mg/day or 15 mg/day, or maintain the 10 mg/day dose. In both studies, participants took the study drug as an oral tablet once per day before breakfast. The primary outcome of the 2-week randomised trial was the change from baseline (ie, last week of the 2-week run-in) in the frequency of spontaneous bowel movements during week 1 of treatment. The primary outcome of the 52-week open-label trial was safety (type, severity, and incidence of adverse drug reactions) at all times from treatment initiation. All efficacy analyses were based on the modified intention-to-treat (ITT) population without imputation for any missing data. Safety analyses included all patients who received at least one dose of study drug. These trials are registered with the Japan Pharmaceutical Information Center (numbers JapicCTI-153061 and JapicCTI-153062) and have been completed. Findings: Between Nov 4, 2015, and June 11, 2016, we assigned 133 patients to treatment in the 2-week randomised trial: 70 to elobixibat (69 included in the modified ITT and safety populations) and 63 to placebo. The frequency of spontaneous bowel movements per week during week 1 of treatment was greater with elobixibat (least-squares mean 6·4, 95% CI 5·3–7·6) than with placebo (1·7, 1·2–2·2), p<0·0001). Between Oct 31, 2015, and March 15, 2017, we allocated 341 patients to 52 weeks of elobixibat (340 included in the modified ITT and safety populations). 163 (48%) patients in the 52-week trial had an adverse drug reaction, the most common of which were mild gastrointestinal disorders (in 135 [40%] patients). Inguinal hernia was reported in one patient with elobixibat in the 52-week study as a moderate adverse drug reaction. The most common adverse drug reactions in both trials were mild abdominal pain (13 [19%] patients with elobixibat and one [2%] with placebo in the 2-week randomised trial, and 82 [24%] patients in the 52-week trial) and diarrhoea (nine [13%] patients with elobixibat and none with placebo in the 2-week randomised trial and 50 [15%] in the 52-week trial). Interpretation: Elobixibat resolved constipation in the short-term, and was well tolerated with both short-term and long-term treatment. The evidence supports the use of this novel approach to increase intracolonic concentrations of endogenous bile acid for the treatment of chronic constipation. Funding: EA Pharma and Mochida Pharmaceutical.
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