Influence of urate-lowering therapies on renal handling of uric acid.

The purpose of this study is to investigate the effect of urate-lowering therapies (ULTs) on renal uric acid excretion in gout patients. This prospective observational study involved 106 primary gout patients and 51 healthy controls. Gout patients received ULT with either xanthine oxidase inhibitors or the uricosuric agent benzbromarone. Parameters such as 24-h urinary uric acid, creatinine clearance, uric acid clearance, glomerular filtration load of uric acid, fractional excretion of uric acid, excretion of uric acid per volume of glomerular filtration, and urinary uric acid to urinary creatinine ratio were used to evaluate the pre- and post-treatment renal capacity for uric acid clearance in gout patients and were compared with the values in the healthy controls. Compared to healthy controls, gout patients had higher glomerular filtration load of uric acid and lower uric acid clearance, creatinine clearance, and fractional uric acid excretion. After ULT, both the xanthine oxidase inhibitor group and benzbromarone group patients showed reduction in glomerular filtration load of uric acid. Creatinine clearance was significantly improved in the xanthine oxidase inhibitor group. Excretion function was remarkably enhanced in patients who reached the treatment target (serum uric acid <6 mg/dl). Changes in glomerular uric acid filtration load were significantly correlated with changes in serum urate levels. Gout patients have impaired renal uric acid excretion. ULTs reduce renal urate load and enhance the renal capacity of uric acid clearance. Xanthine oxidase inhibitors showed superiority over benzbromarone in improving renal function.