Desipramine: Co-administration of drugs that are CYP2D6 substrates (such as desipramine) with ULORIC are not expected to require dose adjustment. Febuxostat was shown to be a weak inhibitor of CYP2D6 in vitro and in vivo. Administration of ULORIC (120 mg once daily) with desipramine (25 mg) resulted in an increase in C (16%) and AUC (22%) of desipramine, which was associated with a 17% decrease in the 2-hydroxydesipramine to desipramine metabolic ratio (based on AUC).

Carcinogenesis: Two-year carcinogenicity studies were conducted in F344 rats and B6C3F1 mice. Increased transitional cell papilloma and carcinoma of urinary bladder was observed at 24 mg per kg (25 times the human plasma exposure at maximum recommended human dose of 80 mg per day) and 18.75 mg per kg (12.5 times the human plasma exposure at 80 mg per day) in male rats and female mice, respectively. The urinary bladder neoplasms were secondary to calculus formation in the kidney and urinary bladder.

Mutagenesis: Febuxostat showed a positive mutagenic response in a chromosomal aberration assay in a Chinese hamster lung fibroblast cell line with and without metabolic activation in vitro. Febuxostat was negative in the in vitro Ames assay and chromosomal aberration test in human peripheral lymphocytes, and L5178Y mouse lymphoma cell line, and in vivo tests in mouse micronucleus, rat unscheduled DNA synthesis and rat bone marrow cells.

Impairment of Fertility: Febuxostat at oral doses up to 48 mg per kg per day (approximately 35 times the human plasma exposure at 80 mg per day) had no effect on fertility and reproductive performance of male and female rats.

A 12-month toxicity study in beagle dogs showed deposition of xanthine crystals and calculi in kidneys at 15 mg per kg (approximately 4 times the human plasma exposure at 80 mg per day). A similar effect of calculus formation was noted in rats in a six-month study due to deposition of xanthine crystals at 48 mg per kg (approximately 35 times the human plasma exposure at 80 mg per day).

A serum uric acid level of less than 6 mg per dL is the goal of anti-hyperuricemic therapy and has been established as appropriate for the treatment of gout.

The efficacy of ULORIC was demonstrated in three randomized, double-blind, controlled trials in patients with hyperuricemia and gout. Hyperuricemia was defined as a baseline serum uric acid level ≥ 8 mg per dL.

Study 1 randomized patients to: ULORIC 40 mg daily, ULORIC 80 mg daily, or allopurinol (300 mg daily for patients with estimated creatinine clearance (Cl) ≥ 60 mL per min or 200 mg daily for patients with estimated Cl ≥ 30 mL per min and ≤ 59 mL per min). The duration of Study 1 was 6 months.

Study 2 randomized patients to: placebo, ULORIC 80 mg daily, ULORIC 120 mg daily, ULORIC 240 mg daily or allopurinol (300 mg daily for patients with a baseline serum creatinine ≤ 1.5 mg per dL or 100 mg daily for patients with a baseline serum creatinine greater than 1.5 mg per dL and ≤ 2 mg per dL). The duration of Study 2 was 6 months.

Study 3, a 1-year study, randomized patients to: ULORIC 80 mg daily, ULORIC 120 mg daily, or allopurinol 300 mg daily. Subjects who completed Study 2 and Study 3 were eligible to enroll in a phase 3 long-term extension study in which subjects received treatment with ULORIC for over three years.

In all three studies, subjects received naproxen 250 mg twice daily or colchicine 0.6 mg once or twice daily for