Rasburicase for Gout

Rasburicase is a urate oxidase enzyme engineered from a strain of fungi. It converts uric acid into allantoin that is soluble in water and easily removed by the kidneys in the urine. Rasburicase, brand name Elitek in the US and Fasturtec in Europe, was primarily developed to address hyperuricemia (high uric acid) and renal failure (from hyperuricosuria or high uric acid in urine) resulting from tumor lysis syndrome (TLS).

TLS results from treatment of cancer such as leukemia and lymphomas. TLS is actually a group of metabolic complications that also includes hyperkalemia (high potassium), hyperphosphatemia (high phosphate) and hypocalcemia (low calcium). These are caused by by-products of cell breakdown and death during cancer treatment like chemotherapy.

In the case of hyperuricemia in TLS, Rasburicase is approved by both US Food and Drug Administration and its European counterpart, the European Union’s Committee for Medicinal Products for Human Use. There is no approval however for the use of Rasburicase for gout treatment. This has not prevented doctors and researchers from conducting clinical trials using Rasburicase for gout, particularly for tophaceous gout. The results of these trials show promising results as discussed below.

Rasburicase for Gout – Results

In one trial published in Nature Clinical Practice Rheumatology, Rasburicase successfully treated a 56-year old woman with a 16-month severe case of tophaceous gout. This woman was allergic to conventional uric acid lowering drug Allopurinol. Rasburicase was well-received, with no allergic reactions. Acute gout attacks were noted during the first 3 to 4 infusions of Rasburicase but no attacks were noted after the sixth infusion. Gout tophi disappeared as well and renal function stabilized.

Another study conducted on a 33-year old woman in Switzerland suffering from tophaceous gout after kidney transplant showed the same positive results. This woman was also allergic to allopurinol. Rasburicase was given over a 3-year period and was well-received by the patient with only mild joint inflammations noted. The study was published in Oxford Journal’s Nephrology Dialysis Transplantation.

The fact remains that both the commonly marketed brands of Rasburicase, Elitek and Fasturtec, are only approved for wide use in high uric acid associated with TLS. Another urate oxidase, Pegloticase (brand name Krystexxa) has been approved by US FDA for refractory chronic gout or RCG. RCG is severe recurrent gout that is resistant to conventional gout medications but not necessarily similar to formation of tophi (hardened uric acid crystals in the joints) as in the case of tophaceous gout.

With additional studies and information derived from them, using Rasburicase for gout treatment may well become another viable option, especially severe tophaceous gout. For the meantime, gout patients that no dot respond well to conventional uric acid lowering drugs such as Allopurinol, Febuxostat, Probenecid, etc. can discuss with their doctor the possibility of using Pegloticase as a treatment.