Assessment of the Effects of Renal Impairment on the Pharmacokinetic Profile of Fesoterodine

The effects of renal impairment on the pharmacokinetics of a single 4-mg oral dose of fesoterodine are assessed in 8 healthy subjects and 8 subjects each with mild, moderate, or severe renal impairment. Compared with findings in healthy subjects, the maximum concentration in plasma of 5-hydroxymethyl tolterodine (5-HMT), the principal active moiety of fesoterodine, increases by 1.4-, 1.5-, and 2.0-fold and area under the curve increases by 1.6-, 1.8-, and 2.3-fold in subjects with mild, moderate, and severe renal impairment, respectively. There is a clear correlation between the renal clearance of 5-HMT and creatinine clearance. The median time of observed maximum drug concentration (5-6 hours) and mean terminal half-life (6-7 hours) of 5-HMT are unaffected by renal impairment. The unbound fraction of 5-HMT in plasma (0.43-0.54 ng/mL) is comparable across all groups. In conclusion, because of the involvement of both metabolic and renal elimination pathways, only modest increases in 5-HMT exposures are observed in patients with renal impairment.