 PEG-uricase is a recombinant porcine urate oxidase to which multiple strands of polyethylene glycol PEG of average molecular weight 10,000 have been attached. PEGylation is intended to reduce the immunogenicity of uricase, and greatly prolong its circulating life. This mammalian PEG-uricase was non-immunogenic and effective in preventing uric acid nephropathy in a uricase-deficient strain of mice Kelly et al, J Am Soc Nephrol 12:1001-09, 2001. It has been licensed to Savient Pharmaceuticals for clinical development, and has received Orphan Drug designation for the treatment of refractory gout by the FDA Office of Orphan Product Development. 