The purpose of this study is to investigate the safety and effectiveness of a medication called CellCept in treating refractory (has not responded to other treatments) interstitial cystitis.

CellCept belongs to a class of medications called immuno-suppressants. Immuno-suppressants work in the body by reducing the immune system's ability to produce certain reactions that can cause inflammation. In some people, the inflammation produced by their immune system can damage healthy tissues and cause symptoms of pain and discomfort. CellCept is approved by the U.S. Food and Drug Administration (FDA) for use in patients who have had an organ transplant. When used in combination with other drugs, CellCept helps to prevent the rejection of the transplanted organ and is used widely in patients who have received kidney, liver and heart transplants. CellCept is also frequently used but not FDA approved for the treatment of severe rheumatoid arthritis which is a disease caused when the body's immune system acts against healthy tissues in the joints.

Due to its special activity, CellCept may be useful in treating certain inflammatory diseases or conditions like interstitial cystitis.

Interstitial Cystitis (IC) is a bladder syndrome characterized as painful, debilitating and chronic, with no universally successful treatment option currently available. Characteristic symptoms include pain with bladder filling, and marked urinary frequency (to relieve pain). The only FDA-approved oral medication for treatment of IC is pentosan polysulfate (Elmiron), recently demonstrated by our collaborative research network to perform with little more efficacy than placebo (ref), and which is expensive and has associated side effects. Current clinical treatment protocols are empiric and usually aimed at relieving pain. There is a pressing need for an effective oral medication for treatment of IC. The presentation of symptoms can be quite variable among patients, suggesting that IC is a multi-factorial syndrome with several proposed etiologies, some of which may be interrelated.

Inclusion Criteria:

• Participant at least 18 years of age and received a diagnosis of PBS/IC, confirmed by cystoscopy and hydrodistention in the past with findings of glomerulations and/or ulceration.
• Participant has symptoms of urinary frequency and pain/discomfort (at least 4 on each 0-10 Likert scale) at entry.
• Participant failed at least 24 weeks of active treatment with a minimum of 3 standard forms of therapy (including hydrodistension) or combination of therapies for PBS/IC.
• Participant will receive cystoscopy to be performed in the office at baseline visit before randomization if none has been conducted within the previous 24 weeks. Cystoscopy results must show no unevaluated lesions.
• Female participants with a cervix are required to have Pap smear exam within the past 12 months prior to enrollment with normal results reported.
• Participant (female) with child-bearing potential must agree to use two reliable/medically approved methods of birth control.

Exclusion Criteria:

• History of cancer or known pre-malignant conditions, including skin cancer.
• History of bladder calculus, tuberculous cystitis; neurologic disease affecting bladder function.
• Current immunocompromised condition, including current or chronic treatment with immunosuppressive agents, or known positive for HIV (positive antibody confirmed by Western Blot or IFA); active tuberculosis requiring on-going therapy; current systemic steroid treatment at any dose.
• Liver function test or creatinine results greater than 2x the upper limit of normal at home institution laboratory.
• Any baseline leukopenia (an absolute neutrophil count <1,500/µL), thrombocytopenia (a platelet count less than 150,000/microL), or anemia - HGB < 12 or < 11 g/dLin men and in women respectively.
• Is seropositive for Hepatitis B surface antigen; or is seropositive for Hepatitis B surface antibody (if not previously vaccinated); is seropositive for Hepatitis C antibody or HIV antigen or antibody.
• Allergy or hypersensitivity to study medication.
• Unable to void spontaneously.
• Active urethral or ureteral calculi, urethral diverticulum.
• Any severe debilitating or urgent concurrent medical condition.
• Previous cytoxan/cyclophosphamide treatment, pelvic radiation therapy; augmentation cystoplasty, cystectomy, or cystolysis; neurectomy.
• Participants with history of treatment for genital tract dysplasia or genital warts or genital herpes.
• Patients with active or a history of peptic ulcer disease, inflammatory bowel disease or gastrointestinal bleeding.
• Patients with hypertension not adequately controlled with medication.
• Patient currently taking H2 blockers or proton pump inhibitors.
• Patients who cannot tolerate or refuse an office cystoscopy.

Exclusion criteria for men only:

• Currently being treated for chronic bacterial prostatitis, as documented by a positive urine culture or prior history of recurrent bacterial urinary infections.
• Unevaluated suspicious prostate exam.

Exclusion criteria for women only:

• Lactation, pregnancy, or refusal of two types of (medically approved/reliable) birth control in women of child-bearing potential.
• Pain, frequency, urgency symptoms present only during menses.