The purpose of this multi-center, double-blind (neither the patient nor the physician knows whether drug or placebo is being taken, or at what dosage), randomized (patients are assigned different treatments based on chance), parallel group trial is to evaluate the effectiveness and safety of two doses of pentosan polysulfate sodium (100 mg once a day and 100 mg three times a day) versus placebo for 24 weeks for the relief of bladder pain or discomfort associated with interstitial cystitis. The hypothesis of the study is that there is no treatment difference in the proportion of responders at study endpoint (Week 24). Effectiveness will be assessed based on the reduction in the O'Leary-Sant Interstitial Cystitis Symptom Index (ICSI) total score. Safety assessments include vital signs, laboratory tests, adverse events and physical exams. Patients will receive one of the following study treatments by mouth each day for 24 weeks: pentosan polysulfate sodium 100 mg once a day group - one pentosan polysulfate sodium 100 mg capsule in the morning, and one matching placebo capsule in the afternoon and evening; pentosan polysulfate sodium 100 mg capsule three times a day group - one pentosan polysulfate sodium 100 mg capsule in the morning, afternoon and evening; placebo group - one placebo capsule in the morning, afternoon and evening
