Efficacy of solifenacin on irritable bowel syndrome with diarrhea: Open-label prospective pilot trial

Background/Aims: Solifenacin, a muscarinic type 3 receptor antagonist, is used to treat overactive bladder in adults. The aim of this study is to examine the efficacy of solifenacin on the symptomatic relief of diarrhea predominant irritable bowel syndrome (IBS-D). Methods: A total of 20 patients with IBS-D were enrolled. After a 2-week observation period, all participants received solifenacin for 6 weeks. Subsequently, the administration of solifenacin was discontinued and ramosetron, a serotonin 3 receptor antagonist, was administered for 4 weeks. Overall improvement, the IBS-symptom severity scale (IBS-SSS), and frequency of defecation were assessed. Results: Six weeks after initiation of solifenacin treatment and 4 weeks after initiation of ramosetron treatment, overall improvement was observed in 19 out of 20 (95%) and 17 out of 20 (85%) participants, respectively. At 2 weeks after initiation of solifenacin, overall improvement was observed in 16 out of 20 participants (80%). Total IBS-SSS scores at 2 and 6 weeks after the administration of solifenacin, and at 4 weeks after administration of ramosetron, were significantly lower than those at week 0. Compared to before administration, the participants' quality of life and frequency of defecation were significantly lower in all participants at 2 and 6 weeks after the administration of solifenacin and at 4 weeks after administration of ramosetron. Conclusions: The efficacy of solifenacin in the treatment of IBS with diarrhea was not inferior to that of ramosetron. Further placebo-controlled parallel studies are needed.