Objectives: Linaclotide is a guanylate cyclase-C agonist approved in the United States, Canada, and Mexico at a once-daily 145-μg dose for the treatment of chronic idiopathic constipation (CIC); a once-daily 72-μg dose for CIC recently received FDA approval. The trial objective was to evaluate the efficacy and safety of a 72-μg linaclotide dose in CIC patients.
Methods: This double-blind, placebo-controlled trial randomized patients with CIC (Rome III criteria) to once-daily linaclotide 72 μg or 145 μg, or placebo for 12 weeks. The primary endpoint, 12-week complete spontaneous bowel movement (CSBM) overall responder, required patients to have ≥3 CSBMs and an increase of ≥1 CSBM per week from baseline in the same week for ≥9 of 12 weeks of the treatment period. Secondary endpoints included 12-week change from baseline in bowel (SBM and CSBM frequency, stool consistency, straining) and abdominal (bloating, discomfort) symptoms, monthly CSBM responders, and 12-week CSBM responders among patients who averaged >1 SBM/week at baseline. Sustained response (12-week CSBM overall responders who met weekly criteria for 3 of the 4 final weeks (weeks 9-12) of treatment) was evaluated as an additional endpoint. Adverse events (AEs) were monitored.
Results: The intent-to-treat population included 1,223 patients (mean age=46 years, female=77%, white=71%). The primary endpoint was met by 13.4% of linaclotide 72-μg patients vs. 4.7% of placebo patients (P<0.0001, odds ratio=3.0; statistically significant controlling for multiplicity). Sustained response was achieved by 12.4% of linaclotide 72-μg patients vs. 4.2% of placebo patients (nominal P<0.0001). Linaclotide 72-μg patients met 9-of-10 secondary endpoints vs. placebo (P<0.05; abdominal discomfort, P=0.1028). Patients treated with linaclotide 145 μg also improved CIC symptoms for the primary (12.4%) and sustained responder endpoint parameters (11.4%) and for all 10 of the secondary endpoint parameters including abdominal discomfort (P<0.05). Diarrhea, the most common AE, was mild in most instances and resulted in discontinuation of 0, 2.4%, and 3.2% of patients in the placebo, linaclotide 72-μg, and linaclotide 145-μg groups, respectively.
Conclusions: Once-daily linaclotide 72 μg significantly improved CIC symptoms in both men and women with a low rate of discontinuation due to diarrhea over 12 weeks of treatment.