Gout is an intermittent inflammatory arthritis caused by the formation of uric acid crystals in joint fluid. In all mammals except humans and some other primates, the enzyme uricase breaks down uric acid into the highly soluble allantoin. Elevated uric acid levels can result in the formation of monosodium urate crystals; in the joints, urate crystals can cause intensely painful inflammation, and in the kidneys, they can damage kidney function and form stones. Over time, urate crystals and inflammatory cells can be deposited in soft tissue, forming masses called tophi. Gout is a common disease with increasing incidence, driven mainly by an aging population (the likelihood of having elevated levels of uric acid increases sharply past age 65). According to the NHANES (National Ambulatory Care survey of the CDC), over 5 million adults report having been diagnosed with gout.
Patients with elevated uric acid may remain asymptomatic, though many of them will go on to experience one or more attacks of acute gout. An acute gout flare may last for several days and is managed mainly by treating pain and inflammation. For patients with tophaceous gout or with more than three attacks per year, chronic therapy with uric acid lowering drugs is warranted – the majority of patients needing chronic therapy end up on allopurinol or febuxostat (Uloric), drugs that block the synthesis of uric acid. While many patients benefit from first line uric acid-lowering drugs, some gout patients experience an inadequate response or are unable to tolerate allopurinol. We believe up to 10% of gout patients have an inadequate response to therapy; some of these patients would benefit from a change in their treatment regimen. We believe about 50,000 of these patients are truly refractory to current treatments and have few therapeutic options, and several-fold more whose gout is inadequately managed.