• Percentage of Subjects Whose Serum Urate Level Decreases to or is Maintained at <6.0 mg/dL at Month 6 Visit. [ Time Frame: Month 6 ] [ Designated as safety issue: No ]
• Percentage of Subjects Whose Serum Urate Level Decreases to or is Maintained at <6.0 mg/dL at Month 12 Visit. [ Time Frame: Month 12 ] [ Designated as safety issue: No ]
• Percentage of Subjects Whose Serum Urate Level Decreases to or is Maintained at <6.0 mg/dL at Month 18 Visit. [ Time Frame: Month 18 ] [ Designated as safety issue: No ]
• Percentage of Subjects Whose Serum Urate Level Decreases to or is Maintained at <6.0 mg/dL at Month 24 Visit. [ Time Frame: Month 24 ] [ Designated as safety issue: No ]
• Percentage of Subjects Whose Serum Urate Level Decreases to or is Maintained at <6.0 mg/dL at Month 36 Visit. [ Time Frame: Month 36 ] [ Designated as safety issue: No ]
• Percentage of Subjects Whose Serum Urate Level Decreases to or is Maintained at <6.0 mg/dL at Month 48 Visit. [ Time Frame: Month 48 ] [ Designated as safety issue: No ]
• Percentage of Subjects Whose Serum Urate Level Decreases to or is Maintained at <6.0 mg/dL at Month 60 Visit. [ Time Frame: Month 60 ] [ Designated as safety issue: No ]
• Percentage of Subjects Whose Serum Urate Level Decreases to or is Maintained at <6.0 mg/dL at Final Visit. [ Time Frame: Last Visit on treatment (up to 66 months). ] [ Designated as safety issue: No ]

• Percent Change in Serum Urate Levels From Baseline at Month 6 Visit. [ Time Frame: Baseline and Month 6 ] [ Designated as safety issue: No ]
• Percent Change in Serum Urate Levels From Baseline at Month 12 Visit. [ Time Frame: Baseline and Month 12 ] [ Designated as safety issue: No ]
• Percent Change in Serum Urate Levels From Baseline at Month 18 Visit. [ Time Frame: Baseline and Month 18 ] [ Designated as safety issue: No ]
• Percent Change in Serum Urate Levels From Baseline at Month 24 Visit. [ Time Frame: Baseline and Month 24 ] [ Designated as safety issue: No ]
• Percent Change in Serum Urate Levels From Baseline at Month 36 Visit. [ Time Frame: Baseline and Month 36 ] [ Designated as safety issue: No ]
• Percent Change in Serum Urate Levels From Baseline at Month 48 Visit. [ Time Frame: Baseline and Month 48 ] [ Designated as safety issue: No ]
• Percent Change in Serum Urate Levels From Baseline at Month 60 Visit. [ Time Frame: Baseline and Month 60 ] [ Designated as safety issue: No ]
• Percent Change in Serum Urate Levels From Baseline at Final Visit. [ Time Frame: Baseline and Last Visit on treatment (up to 66 months). ] [ Designated as safety issue: No ]

The purpose of this study is to evaluate the long-term safety of febuxostat in maintaining serum urate levels within clinically acceptable levels in subjects with gout.

Uric acid is the end product of purine degradation in humans. Hyperuricemia, a urate concentration in serum exceeding the limit of urate solubility (approximately 7.0 milligrams per deciliter [mg/dL]), is a common biochemical abnormality. Aberrations in any of the multiple mechanisms involved in the production and/or excretion of uric acid may increase serum urate concentrations, with persistent hyperuricemia as a marker for extracellular fluid monosodium urate supersaturation. As such, hyperuricemia is a necessary (but often not sufficient) risk factor for monosodium urate crystal deposition in tissues and is the fundamental pathophysiological process underlying the clinical manifestations of gout, which is a chronic disease characterized by urate crystal formation and deposition in joints and bones. Gout may progress from episodic attacks of acute inflammatory arthritis to a disabling chronic disorder characterized by deforming arthropathy; destructive deposits of urate crystals (tophi) in bones, joints, and other organs; structural and functional renal impairment due to interstitial urate crystal deposition; and urinary tract stones composed entirely or in part of uric acid crystals. Management of gout requires chronic treatment aimed at lowering serum urate into a subsaturating range (usually <6.0 mg/dL) in which crystal formation and deposition are prevented or reversed.

Febuxostat (TMX-67) is a non-purine selective xanthine oxidase inhibitor being developed as an orally administered agent for management of hyperuricemia in patients with gout.

Subjects who want to participate in this study will have successfully completed study TMX-00-004 (NCT00174967).

All participants will initially receive an 80 mg dose. Dose titrations will occur in order to obtain and maintain clinically acceptable serum urate levels.

Inclusion Criteria:

• Hyperuricemia (serum uric acid ≥8.0 mg/dL upon entering parent study TMX-00-004).
• Must meet American College of Rheumatology criteria for gout.
• Must have adequate renal function (serum creatinine <1.5 mg/dL).
• Must have completed four weeks of double-blind dosing in Study TMX-00-004.
• Must not have experienced any serious study drug-related Adverse Events in Study TMX 00-004.
• Females of childbearing potential who are sexually active must agree to use adequate contraception, and can neither be pregnant nor lactating from Screening throughout the duration of the study.

Exclusion Criteria:

• History of xanthinuria
• Alcohol consumption >14/week
• Has a History of significant concomitant illness
• Has active liver disease.
• Has a body mass index greater than 50 kg/m2
• Any other significant medical condition that would interfere with the treatment, safety or compliance with the protocol, as defined by the investigator.