A Multi-Center Trial to Determine the Safety and Efficacy of LX1033 in Subjects With Diarrhea-Predominant Irritable Bowel Syndrome

Inclusion Criteria: * Male and female subjects, aged 18 to 70 years, with diarrhea-predominant IBS (IBS-D) with symptom onset at least 6 months prior to diagnosis * Two or more days per week with at least one stool with a consistency of Type 6 or 7 (Bristol Stool Form Scale) * Weekly average of worst abdominal pain in past 24 hours score of greater than or equal to 3.0 using a 0-10 point scale * Ability to provide written, informed consent Exclusion Criteria: * Inability to discontinue any current drug therapy for IBS, with the exception of bulking agents. Subjects will be allowed up to 2 doses of loperamide per week as rescue medication. * Subjects who score severe abdominal pain (rated 7 or higher) 5 or more days per week * Concomitant use of opioid analgesic drugs or drugs that affect bowel motility * Any abnormalities or conditions deemed by the investigator as clinically significant