Introduction: Plecanatide is an orally administered 16 amino acid analog of the human GI peptide uroguanylin (UG). UG binds to and activates the guanylate cyclase-C (GC-C) receptor in the proximal small intestine in a pH-dependent manner, contributing to fluid secretion and normal bowel function. Plecanatide similarly binds to GC-C in a pH-dependent manner and is being developed for the treatment of CIC. Results are presented from the recently completed long-term, open-label study of plecanatide in CIC patients. Methods: The primary objective of this multicenter study was to assess the long term safety and tolerability of once daily plecanatide for the treatment of CIC. Patients who completed a previous double-blind study (Phase 2b or either of the two Phase 3 studies), select patients who had screen failed for either of the Phase 3 studies, or select patients who had not previously been treated with plecanatide may have been eligible for this study. Enrolled patients received 52 weeks (3mg) or up to 72 weeks (6mg) of plecanatide. Dose adjustments were not permitted. In addition to spontaneous adverse event (AE) reporting, patients completed Patient Global Assessment (PGA) questionnaires which included measures of patient satisfaction and desire to continue treatment on a scale of 1 to 5 (higher scores are better). Results: There were 2370 patient exposures in this study with the majority (90.5%) receiving treatment with the 6 mg dose; 1932 (81.5%) completed or were receiving study drug at the time the study met its enrollment goal and was ended. Treatment emergent adverse events (TEAEs) were qualitatively and quantitatively similar to those observed in prior double blindstudies. The most common AEs were diarrhea (7.1%) and urinary tract infection (2.2%). The remainder of the AEs occurred in < 2% of the patients. AEs leading to discontinuation occurred in 5.3% of patients; diarrhea leading to discontinuation occurred in 3.1%. The majority of TEAEs were mild or moderate in intensity and were generally considered not related to plecanatide treatment. The median score for treatment satisfaction was 4.0 (4=quite satisfied) and for continuation of treatment was 4.0 (4=quite likely). Conclusion: In this long term trial of CIC patients, plecanatide was well tolerated with low AE rates and low discontinuation rates. PGA assessments indicate that the patients were both satisfied with their treatment and likely to continue with plecanatide therapy.