Linaclotide for Irritable Bowel Syndrome With Constipation: A 26-Week, Randomized, Double-blind, Placebo-Controlled Trial to Evaluate Efficacy and Safety

OBJECTIVES: Linaclotide is a minimally absorbed peptide guanylate cyclase-C agonist. The objective of this trial was to determine the efficacy and safety of linaclotide treatment in patients with irritable bowel syndrome with constipation (IBS-C) over 26 weeks. METHODS: This phase 3, double-blind, parallel-group, placebo-controlled trial randomized IBS-C patients to placebo or 290 μg of oral linaclotide once daily for a 26-week treatment period. The primary and the secondary efficacy assessments were evaluated over the first 12 weeks of treatment. Primary end points included the Food and Drug Administration's (FDA's) end point for IBS-C (responder: a patient who reported (i) improvement of ≥30% from baseline in average daily worst abdominal pain score and (ii) increase of ≥1 complete spontaneous bowel movement (CSBM) from baseline, both in the same week for ≥6/12 weeks) and three other primary end points, based on improvements in abdominal pain and CSBMs for 9/12 weeks. Adverse events (AEs) were monitored. RESULTS: In all, 804 patients (mean age=44 years, female=90%, white=78%) were evaluated; 33.7% of linaclotide-treated patients were FDA end point responders, vs. 13.9% of placebo-treated patients (P<0.0001) (number needed to treat=5.1, 95% confidence interval (CI): 3.9, 7.1). The pain responder criterion of the FDA end point was met by 48.9% of linaclotide-treated patients vs. 34.5% of placebo-treated patients (number needed to treat=7.0, 95% CI: 4.7, 13.1), and the CSBM responder criterion was met by 47.6% of linaclotide-treated patients, vs. 22.6% of placebo patients (number needed to treat=4.0, 95% CI: 3.2, 5.4). Remaining primary end points (P<0.0001) and all secondary end points (P<0.001), including abdominal pain, abdominal bloating, and bowel symptoms (SBM and CSBM rates, Bristol Stool Form Scale (BSFS) score, and straining), were also statistically significantly improved with linaclotide vs. placebo. Statistically significant differences from placebo were observed for responder and continuous end points over 26 weeks of treatment. AE incidence was similar between treatment groups, except for diarrhea, which caused discontinuation in 4.5% of linaclotide patients vs. 0.2% of placebo patients. CONCLUSIONS: Linaclotide 290 μg once daily significantly improved abdominal and bowel symptoms associated with IBS-C over 26 weeks of treatment.