Evaluation of the Efficacy and Safety of Lubiprostone in Adults With Mixed or Unsubtyped Irritable Bowel Syndrome

To assess the efficacy and safety of oral lubiprostone, as compared to matching placebo,
when administered orally (at 8 mcg twice daily [BID]) in subjects diagnosed with
IBS-M/IBS-U.

Inclusion Criteria:

- Subject meets the diagnosis of IBS-M or IBS-U as confirmed using the adapted ROME III
Diagnostic Questionnaire for Adult Functional GI Disorders.

- Subject Screening diary entries must show an average worst abdominal pain in the past
24 hours score of at least 4 on a 11-point scale.

- Subject must be on a stable dose of selective serotonin re-uptake inhibitors (SSRIs),
serotonin-specific reuptake inhibitor (SNRIs), or monoamine oxidase inhibitors (MAO)
inhibitors if taking antidepressants.

Exclusion Criteria:

- Subject has current diagnosis of IBS with diarrhea (IBS-D) or IBS with constipation
(IBS-C), according to Rome III Criteria.

- Any gastrointestinal (GI) condition, other than IBS-related, affecting GI motility or
defecation.

- Medical/surgical condition that might interfere with the absorption, distribution,
metabolism, or excretion of the study medication.