• The primary efficacy parameter is the proportion of patients with at least a 30% reduction in the patient-completed O'Leary-Sant Interstitial Cystitis Symptom Index (ICSI) from baseline to Week 24 or last visit
  

• Proportion of patients with at least a 4-point reduction in ICSI from baseline to Week 24 or last visit; proportion of patients with >= 50% improvement in Patient Overall Rating of Improvement of Symptoms (PORIS) from baseline to Week 24 or last visit
  

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 asessed based on the reduction in the O'Leary-Sant Interstitial Cystitis Symptom Index (ICSI) total score. Safety assessments include vitals 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

Inclusion Criteria:

• Must have a total score of 8 or greater on the O'Leary-Sant Interstitial Cystitis Symptom Index (ICSI) and a score of > 0 on each of the 4 questions on the ICSI
• Must have experienced bladder pain, urinary urgency and urinary frequency, each not related to a urinary tract infection, for at least 6 months prior to entry into the study
• Must have averaged >= 10 voids per day (>=30 voids over 3 consecutive days) and averaged >= 1 void at night
• Urine culture showing no evidence of urinary tract infection
• Urine cytology showing no evidence of neoplastic cells

Exclusion Criteria:

• Scheduled for or use of intravesical therapy (eg, bladder distention, dimethyl sulfoxide) during or within 4 weeks prior to the study
• Patients who have had cytoscopic evaluation within 4 weeks prior to the study
• Patients who are currently (within last month) receiving other medications that may affect symptoms of interstitial cystitis (ie, antidepressants, antihistamines, antispasmodics, anticholoiergics)
• Patients who are chronic users of Schedule II narcotics or who are using any scheduled narcotics at the time of study entry
• Patients taking coumadin, anticoagulants, heparin, or thrombolytic agents such as tissue plasminogen activator and streptokinase