A pharmacokinetic-pharmacodynamic study of a single dose of febuxostat in healthy subjects.

AIMS: To examine the pharmacokinetic-phamacodynamic (PK-PD) relationships of plasma febuxostat and serum urate and the effect of a single dose of the drug on renal excretion and fractional clearance of urate (FCU). METHODS: Blood and urine samples were collected at baseline and up to 145 h following administration of febuxostat (80 mg) to healthy subjects (n=9). Plasma febuxostat and serum and urinary urate and creatinine concentrations were determined. Febuxostat pharmacokinetics were estimated using a two-compartment model with first order absorption. An Emax PK-PD model was fitted to mean febuxostat and urate concentrations. Urinary urate excretion and FCU were calculated pre- and post-dose. RESULTS: Maximum mean plasma concentration of febuxostat (2.7 mg l-1 ) was observed 1.2 h after dosage. Febuxostat initial and terminal half-lives were 2.0 ± 1.0 h and 14.0 ± 4.7 h (mean ± SD), respectively. The majority (81%) of the drug was eliminated in the 9 h after dosing. Serum urate declined slowly achieving mean nadir (0.20 mmol l-1 ) at 24 h. The IC50 (plasma febuxostat concentration that inhibits urate production by 50%) was 0.11 ± 0.09 mg l-1 (mean ± SD). Urinary urate excretion changed in parallel with serum urate. There was no systematic or significant change in FCU from baseline. CONCLUSION: The PK-PD model could potentially be used to individualise febuxostat treatment and improve clinical outcomes. Single dose of febuxostat does not affect the efficiency of the kidney to excrete urate. Further investigations are required to confirm the present results following multiple dosing with febuxostat.