Background  Effective treatments for irritable bowel syndrome with constipation (IBS-C) are lacking.

Aim  To assess the efficacy and safety of lubiprostone in IBS-C.

Methods  A combined analysis was performed among 1171 patients with a Rome II diagnosis of IBS-C in two phase-3 randomized trials of lubiprostone 8 mcg vs. placebo twice daily for 12 weeks. Using a balanced seven-point Likert scale ranging from significantly relieved (+3), to significantly worse (−3), patients responded on their electronic diary to the question: ‘How would you rate your relief of IBS symptoms over the past week compared to how you felt before you entered the study?’. The primary efficacy endpoint was the percentage of overall responders.

Results  Using an intent-to-treat analysis with last observation carried forward, a significantly higher percentage of lubiprostone-treated patients were considered overall responders compared with those treated with placebo (17.9% vs. 10.1%, P = 0.001). Patients treated with lubiprostone reported a similar incidence of adverse events to those treated with placebo.

Conclusions  The percentage of overall responders based on patient-rated assessments of IBS-C symptoms was significantly improved in patients treated with lubiprostone 8 mcg twice daily compared to those treated with placebo. Lubiprostone was well tolerated with a favourable safety profile.