The approval is based on a pair of phase 3, randomized, double-blind, placebo-controlled trials in patients meeting the Rome III criteria for IBS-C. Both trials had identical 12-week treatment phases, while trial 1 had a 14-week continuation phase, and trial 2 included a 4-week withdrawal period. The primary endpoint was proportion of responders in the 12-week treatment period; this was defined as a 30% reduction in abdominal pain score and an increase of at least one complete spontaneous bowel movement on average weekly for at least 6 of the first 12 treatment weeks, compared with placebo. Both trials met this endpoint, with trial 1 showing a 37% response rate with treatment versus 24% with placebo, and trial 2 showing rates of 27% and 19%, respectively. Improvements were seen as early as week 1 and were maintained through the end of treatment.
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The most common treatment-related adverse event was diarrhea, with severe diarrhea reported in 2.5% of treated patients versus 0.2% of placebo patients. Discontinuation rates were low. Tenapanor is contraindicated in IBS-C patients younger than 6 years because of concerns about dehydration, and use should be avoided in patients aged 6-12 years. Safety and efficacy has not been established in patients younger than 18 years. Tenapanor is also contraindicated in patients with known or suspected mechanical gastrointestinal obstruction.
The full prescribing information can be found on the FDA website.