Allopurinol Combination Study

Inclusion Criteria:

1. Male or a post-menopausal or surgically sterile female.

2. 18 - 80 years of age.

3. Has been taking allopurinol as the sole urate lowering therapy for hyperuricemia forat least 6 weeks at a dose between 200 mg and 600 mg per day without an adequateresponse.

4. Has a sUA level ≥ 6 mg/dL at screening.

5. Meets criteria for the diagnosis of gout as per the American Rheumatism Association (ARA) Criteria for the Classification of Acute Arthritis of Primary Gout.

6. Willing and able to give informed consent and adhere to visit/protocol schedules (informed consent must be given before the first study procedure is performed).

7. Subjects entering the optional Extension Period must have completed 28 days of dosingin the Double-Blind Treatment Period and the Day 42 Visit in the Follow-up Periodwithin 4 months and must not have experienced any serious adverse events consideredpossibly related to study drug.

8. Subjects entering the optional Open-Label Extension Period must continue to becompliant with the protocol through Week 44 of the Double-Blind Extension Period andmust not have experienced any serious adverse events considered possibly related tostudy drug.

Exclusion Criteria:

1. Consumes more than 14 drinks of alcohol per week (e.g., 1 drink = 5 oz [150 ml] ofwine, 12 oz [360 ml] of beer, or 1.5 oz [45 ml] of hard liquor).

2. History or suspicion of drug abuse.

3. History of documented or suspected kidney stones.

4. Has rheumatoid arthritis or other autoimmune disease requiring treatment.

5. Documented or suspicion of HIV infection.

6. Positive serology to HCV antibodies (Abs), and/or hepatitis B surface antigen (HBsAg).

7. History of malignancy within 5 years prior to the first dose of study medication,other than non-melanomatous skin cancer or cervical dysplasia.

8. History of cardiac abnormalities, including abnormal and clinically relevant ECGchanges

9. Any condition predisposing to QT prolongation including pathological Q-wave (definedas Q-wave >40 msec or depth > 0.4-0.5 mV).

10. Any use of concomitant medications that prolong the QT/QTc interval within the 14 daysprior to Baseline (Day 1).

11. QT interval corrected for heart rate according to Fridericia (QTcF) > 450 msec atScreening or pre-dose at Baseline (Day 1).

12. Uncontrolled hypertension (above 150/95).

13. Inadequate renal function [serum creatinine >1.5 mg/dL or creatinine clearance < 60mL/min (by Cockroft-Gault formula)].

14. Hemoglobin < 10 g/dL (males) or < 9 g/dL (females).

15. Alanine aminotransferase (ALT) or aspartate aminotransferase (AST) > 2.5 x upper limitof normal (ULN).

16. Gamma glutamyl transferase (GGT) > 3 x ULN.

17. Active peptic ulcer disease requiring treatment.

18. History of xanthinuria, active liver disease, or hepatic dysfunction.

19. Requires therapy with any other urate-lowering medication, other than the studymedications.

20. Requires long-term use of salicylates; diuretics; losartan; azathioprine;mercaptopurine; theophylline; intravenous colchicine; cyclosporine; cyclophosphamide;pyrazinamide; sulfamethoxazole; or trimethoprim.

21. Taking medications known as enzyme inducers (see section 3.7 for listing).

22. Reports receiving a strong or moderate inhibitor of CYP3A4 or a P-gp inhibitor within 1 month prior to study drug dosing, due to potential interactions with colchicine.

23. Acute gout flare (exclusive of chronic synovitis/ arthritis) during theScreening-Period that has not resolved one week prior to the Baseline Visit (Day 0).

24. Pregnant or breast feeding.

25. Has received an investigational medication within 4 weeks prior to the screening visitfor this study.

26. Previously participated in a clinical study involving RDEA806 or RDEA594.

27. Known hypersensitivity or allergy to RDEA594, allopurinol or colchicine or anycomponents in their formulations.

28. Body mass index (BMI) >48 kg/m2.

29. Taking greater than 1000 mg/day of Vitamin C.

30. Any other medical or psychological condition, which in the opinion of the Investigatorand/or Medical Monitor, might create undue risk to the subject or interfere with thesubject's ability to comply with the protocol requirements, or to complete the study.

31. Inadequate renal function after completing the Double-Blind Treatment period prior toentering Double-Blind Extension Period.

32. Requiring treatment with prohibited medications noted in exclusion criteria numbers 20-23 after completing the Double-Blind Treatment Period prior to entering theExtension Period.

33. Clinically relevant medical event as determined by the investigator in consultationwith medical monitor prior to entering the Extension Period.