A Pilot Study of the Effects of Mirabegron on Symptoms in Patients With Interstitial Cystitis

Inclusion Criteria: 1. Participants must be diagnosed with BPS/IC with a minimum O'Leary-Sant score of 8 on the ICSI, as well as 8 on the ICPI. Participants should be stable on their regimen (no increase or change in medications, behavioral treatments or physical therapy in previous 4 weeks prior to starting the study) and be willing to remain on this regimen during the duration of the study. 1. Participant must be stable on current IC/BPS regimen. 2. Participant must have subjective complaints of i. urinary urgency, relieved with voiding or ii. urinary frequency; ≥ 8 voids per day iii. pelvic pain, pressure, hypersensitivity or discomfort 2. Gender of subjects: Participants in this study will be female. Pregnant women and breastfeeding women will be excluded due to unknown risk of study medication on pregnancy and fetus or nursing infants. 3. Age of subjects: Age of participants will range from 18 to 95 years. 4. Racial and ethnic origin: There are no enrollment restrictions based upon race or ethnic origin. The racial and ethnic distribution of participants is entirely based on the population of patients at the study site. 5. Other inclusion criteria: 1. Participant must give written informed consent to participate in the study 2. Participant must be able to make decisions for herself 3. Participant must have a negative urine dip within 7 days prior to start of the study 4. Female participants who are of childbearing age and sexually active with men must agree to use a medically acceptable method of contraception throughout the study period, and for 7 days after the study period. Medically acceptable methods of contraception include abstinence, oral contraceptive pills, hormonal contraceptive patches, diaphragm with or without spermicide, IUD, condoms, depot medroxyprogesterone acetate, subdermal progestin implants, vasectomized partner, or status post surgical sterilization. Exclusion Criteria: To participate in the study subjects must not meet any of the following criteria: 1. Participant is currently pregnant or breastfeeding 2. Participant has a positive urinary pregnancy test at the time of screening 3. Participant is currently or has been on antibiotic therapy with the last 7 days prior to the start of the study 4. Participant is an employee of Astellas, or any other pharmaceutical company or the Pelvic and Sexual Health Institute 5. Participant is currently in another pharmaceutical trial 6. Participant has used anticholinergic medications, tamsulosin or opioid narcarotic medication within the last 30 days prior to the study or during the study period. Participants will be able to use rescue medications for BPS/IC symptom flares including non-opioid narcotics, non-steroidal anti-inflammatory agents, pyridium and uribel. 7. Participant has had bladder hydrodistention or bladder instillations within the last 4 weeks. Participants may have bladder instillations during the study period if necessary for rescue from symptom flares. 8. Participant has used or currently using CYP2D6 substrates, such as thioridazine, flecainide, propafenone, within the last 7 days prior to the study or during study period 9. Participant has used warfarin or digoxin within the last 7 days prior to the study or during the study period 10. Participant has used cyclosporine within the 7 days prior to the study or during the study period 11. Participant has an active S3 nerve stimulator implanted or has had PTNS within 6 months prior to starting the study 12. Participant has not had intravesical botulinum toxin injection in 6 months prior to starting the study 13. Participant has grade III or IV pelvic organ prolapse 14. Participant has been diagnosed with a urinary tract infection within the last 4 weeks prior to starting the study 15. Participant has history of bladder cancer 16. Participant is currently an alcohol or substance abuser, or is a chronic opioid user 17. Participant has history of renal failure (GFR \<30) or liver failure (CHILD score B or C) 18. Participant has urinary retention defined as greater than 150cc post-void residual as diagnosed by catheterization, bladder ultrasound scan or urodynamic testing within the last 14 days. 19. Participant has history of severe uncontrolled blood pressure (defines as systolic greater than or equal to 180mm Hg and/or diastolic blood pressure greater than or equal to 110 mm Hg) 20. Participant has a neurological disease including, but not limited to, multiple sclerosis, Parkinson's disease, Alzheimer's disease, spinal cord injury, brain injury, stroke or dementia 21. Participant has urinary frequency of less than 8 times/day 22. Participant has bladder or lower ureteral calculi 23. Participant has active genital herpes 24. Participant has urethral diverticulum 25. Participant has chemical cystitis 26. Participant has radiation or tuberculosis cystitis 27. Participant has known hypersensitivity to mirabegron or any of the inactive ingredients in the supplied form of mirabegron