Febuxostat Versus Allopurinol or Placebo in Subjects With Hyperuricosuria and Calcium Oxalate Stones

Nephrolithiasis, also called kidney stone disease, occurs in patients with genetic
susceptibility and who may have a broad spectrum of metabolic disorders and other comorbid
conditions (for example obesity or diabetes). These renal stones develop as a result of
supersaturation. Calcium oxalate (CaOx) is the most common type of stone. Reducing the
urinary excretion of uric acid is an established approach for the treatment of CaOx kidney
stones.

The objective of this study is to evaluate treatment with febuxostat compared to allopurinol
or placebo in the reduction of 24-hour urine uric acid (uUA) excretion levels in
hyperuricosuric subjects with a recent history of renal stones and the presence of at least
one CaOx stone larger than or equal to 3 mm as seen on Multidetector Computed Tomographic
Angiography (MDCT).

Subjects participating in this study will be required to make 4 office visits provide 3
urine samples and undergo 2 MDCT scans (a type of x-ray) of their kidneys.