Tenapanor Treatment of Patients With Constipation-Predominant Irritable Bowel Syndrome: A Phase 2, Randomized, Placebo-Controlled Efficacy and Safety Trial

OBJECTIVES: Tenapanor is a first-in-class, small-molecule inhibitor of the gastrointestinal sodium/hydrogen exchanger NHE3. This study assessed the efficacy and safety of tenapanor in patients with constipation-predominant irritable bowel syndrome (IBS-C). METHODS: In this phase 2, double-blind study, patients with IBS-C (Rome III criteria) were randomized (1:1:1:1) to receive tenapanor 5 mg, 20 mg, or 50 mg b.i.d., or placebo b.i.d. for 12 weeks. The primary end point was the complete spontaneous bowel movement (CSBM) responder rate, defined as the proportion of patients reporting an increase from baseline of ≥1 CSBM/week for ≥6/12 treatment weeks. Secondary end points included abdominal symptom responder rates (≥30% score improvement from baseline for ≥6/12 weeks) and a composite responder rate (CSBM and abdominal pain response in the same week for ≥6/12 weeks). RESULTS: Overall, 356 patients were randomized (mean age: 45.7 years; 86.8% women) and 304 completed the study. The CSBM responder rate was significantly higher in the tenapanor 50 mg b.i.d. group than in the placebo group (60.7 vs. 33.7% P<0.001), as was the composite responder rate (50.0 vs. 23.6% P<0.001). Responder rates for abdominal symptoms (pain, discomfort, bloating, cramping, and fullness) were significantly higher in the tenapanor 50 mg b.i.d. group than in the placebo group (all P<0.05). Diarrhea was the most frequent adverse event (tenapanor b.i.d.: 20 mg, 12.4% 50 mg, 11.2%). CONCLUSIONS: Tenapanor 50 mg b.i.d. significantly increased stool frequency and reduced abdominal symptoms in patients with IBS-C. Further research into tenapanor as a potential treatment for these patients is justified.