Study to Evaluate sUA-Lowering Activity, Safety & PK Interaction of Oral BCX4208 & Allopurinol Admin. in Subjects w/Gout

Inclusion Criteria:

1. Age ≥18 to <70 years, with screening sUA > 8.0 mg/dL.
2. Diagnosis of gout according to the criteria of the American Rheumatism Association (1977).
3. Be willing and able to take colchicine 0.6 mg per day or naproxen 250 mg twice daily (with proton pump inhibitor if needed) as prophylaxis for gout flares.
4. Be willing to abstain from blood donations from Day -14 to Day 29/Early Termination.

5. Female participants must be sexually abstinent, sterile, post-menopausal, or on stable contraception.

   • Post-menopausal - females greater ≥ 45 years of age whose last menstrual period, including spotting, was > 1 year ago.
   • Stable contraception - now requires a double barrier method, e.g. condom or diaphragm with spermicide.
6. Male participants must be abstinent, vasectomized or using condoms with spermicide with partners meeting female requirements.

Exclusion Criteria:

1. Unable to tolerate allopurinol.
2. Gout Flare during Screening Period that is resolved less than 2 weeks prior to first treatment.
3. Unstable angina, history of symptomatic arrhythmia, or Class III or IV heart failure.
4. ECG Findings: history of congenital long QT syndrome; QTc interval < 350 msec or > 475 msec.
5. Inadequately controlled hypertension (above either or both 150/95 mm Hg).
6. Moderate or severe renal impairment and/or calculated creatinine clearance <60 mL/min (using Cockcroft-Gault formula).
7. ALT or AST > 2.0 x ULN.
8. CD4+ count by flow cytometry (<500 cells/mm3).
9. Hgb <12 g/dL or > 17 g/dL (males) or < 11 g/dL or > 16 g/dL (females).
10. Hct < 37% or > 51% (males) < 33% or > 47% (females).
11. WBC < 3.7 x 109/L or > 11 x 109/L.
12. Positive Pregnancy Test.
13. Females who are pregnant, breastfeeding or planning a pregnancy with the next 4 months.
14. Positive serology for hepatitis B surface antigen or hepatitis C or HIV type I (HIV Ab).
15. Immunocompromised or on systemic immunosuppressant medications (including anakinra) within 14 days of study dosing.
16. Use of azathioprine or 6-mercatopurine within 14 days of study dosing.
17. Use of HCTZ in doses > 50mg per day within 14 days of study dosing.
18. Recipient of any live, attenuated vaccine within 6 weeks of Screening.
19. Receipt of sUA-lowering drugs, ACTH, within 14 days of study dosing.
20. Use of systemic corticosteroids within 4 weeks prior to study dosing.
21. Clinically significant and relevant drug allergies.
22. Chronic or recurrent infections (3 infections at same site) within 12 months.
23. Cancer within 12 months (except nonmelanomatous localized skin cancer.
24. Alcohol or drug abuse.
25. Investigational drug within 30 days of study dosing.
26. Other medical conditions which, in the opinion of the PI, would jeopardize the safety of the study subject or impact the validity of the study results.