Inclusion Criteria:

1. Outpatients with idiopathic PD according to the UK Parkinson's Disease Society Brain Bank Clinical Diagnosis Criteria.
2. Age 40 years to 80 years.
3. Stable dose of antiparkinsonian medication 4 weeks prior to study entry.
4. Patients must score 1.0 to 3.0 on the Modified Hoehn and Yahr scale.
5. Women of child-bearing potential must use a reliable method of contraception.
6. Must be experiencing symptoms of overactive bladder according to the ICS definition of a minimum voiding 8 or more times/24 hours and a daily average of at least 1 episode of urgency and/or urinary incontinence (urge incontinence predominately as measured by 3IQ diary) per 24 hours during a 3-day micturition diary period. Patients must have documentation of OAB within the last 6 months.
7. The patient must have evidence of PSA less than or equal to 4 (males only) within the last 12 months (obtained from primary care physician).
8. The patient must have had a bladder scan within six months of the screening visit. This scan uses ultrasound technology to measure residual fluid levels in the bladder after urination. This scan must document post void residual of 200 mls or less. A bladder scan printout or a note documenting these findings must be provided before baseline.
9. Clearance from the patient's internist or primary care health provider who has examined the patient within the last 6 months.

Exclusion Criteria:

1. Any illness that in the investigator's opinion preclude participation in this study.
2. Pregnancy or lactation.
3. Concurrent participation in another clinical study.
4. Dementia or other psychiatric illness that prevents the patient from giving informed consent (Mini Mental Status Exam scores less than 27).
5. Legal incapacity or limited legal capacity.
6. History of prostate cancer or Transurethral resection of the prostate (TURP) (males only).
7. Presence of severe renal disease. BUN 50% greater than normal (normal BUN levels should be within a range of 5 to 20 mg/ d L and creatinine between .7 and 1.4 mg/ d L). Labs within the past 12 months will be requested from the patient's health care provider or urologist. If labs are not available within this time-frame or if results are abnormal, labs will be obtained as part of the screening visit.
8. Presence of major hepatic impairment (cirrhosis, viral hepatitis, nonalcoholic steatohepatitis, Wilson's disease, or Hemochromotosis).
9. Currently taking ketaconazole (anti-fungal) or any CYP3A4 inhibitor such as itraconazole, ritonavir, nelfinavir, clarithromycin, or nefazadone.
10. Any history of bladder outflow obstruction or gastrointestinal obstructive disorders.
11. History of narrow angle glaucoma.
12. Patients who have undergone pelvic radiation at any time.

13. Currently taking any of the following medications:

    • Antiarrhythmics: flecainide (Almarytm, Apocard, Ecrinal, Flécaine), digoxin (Lanoxin, Digitek, Lanoxicaps)
    • Antipsychotics: thioridazine (Mellaril, Novorizadine, Thioril)
    • Tricyclic anti-depressants: amitriptyline (Elavil, Tryptanol, Endep, Elatrol, Tryptizol, Trepiline, Laroxyl), amoxapine (Asendin, Asendis, Defanyl, Demolox, Moxadil), clomipramine (Anafranil), desipramine (Norpramin, Pertofrane), imipramine (Antideprin, Deprenil, Deprimin, Deprinol, Depsonil, Dynaprin, Eupramin, Imipramil, Irmin, Janimine, Melipramin, Surplix, Tofranil), nortriptyline (Aventyl, Pamelor, Nortrilen), protriptyline (Vivactil), trimipramine (Stangyl, Surmontil, Rhotrimine)
    • Psychotropics: doxepin (Aponal, Adapine, Sinquan, Sinequan)
    • Anticholinergics/Antispasmodics: trihexyphenidyl (Artane, Aparkan), benztropine (Cogentin), oxybutynin (Ditropan, Ditropan XL, Lyrinel XL, Oxytrol), darifenacin (Enablex), emepronium, flavoxate (Urispas), meladrazine, propiverine, solifenacin (Vesicare), tolterodine (Detrol, Detrol LA), trospium (Sanctura)
    • Selective Serotonin-Norepinephrine Reuptake Inhibitors (SNRI): duloxetine (Cymbalta, Yentreve), Venlafaxine (Effexor, Effexor XR)
    • Arylalkylamines: pseudoephedrine (Sudafed)
    • Anti-androgen: bicalutamide (Casodex, Cosudex, Calutide, Kalumid), finasteride (Proscar, Propecia, Fincar, Finpecia, Finax, Finast, Finara, Finalo, Prosteride, Gefina, Finasterid IVAX), dutasteride (Avodart, Avidart, Avolve, Duagen, Dutas, Dutagen, Duprost), Zoladex (goserelin acetate), Eulexin (flutamide), Lupron (leuprolide acetate)
    • Antihypertensives: prazosin (Minipress, Vasoflex, Hypovase)
    • Estrogens (Menest, Premarin, Premarin IV)
    • Acetylcholinesterase inhibitors (rivastigmine (Exelon), galantamine, (Reminyl, donepezil (Aricept), Tacrine.
    • Memantine (Namenda)
14. Urinary obstruction in male PD patients as diagnosed by a urologist
15. Active urinary tract infection.
16. Patients with a history of chronic severe constipation (by self report)