BLurate , baseline serum urate;fm , fraction of the allopurinol systemically available as oxypurinol; CL/fm , apparent clearance of oxypurinol; V/fm , apparent volume of distribution of oxypurinol; Kfm , combined absorption and formation rate constant; Imax , maximum inhibitory effect of oxypurinol on xanthine dehydrogenase to inhibit urate production; IC50 , oxypurinol concentration at half maximum inhibitory effect; CrCL , creatinine clearance calculated using ideal body weight; FFM, fat free mass;Cssoxy , steady-state plasma oxypurinol concentration