Objective: Fesoterodine, a new antimuscarinic agent for overactive bladder, undergoes immediate and extensive hydrolysis by nonspecific esterases to 5-hydroxymethyl tolterodine (5-HMT), the metabolite principally responsible for its antimuscarinic activity. Formation of 5-HMT does not require cytochrome P450 (CYP)-mediated metabolism, but its further metabolism and inactivation involves CYP3A4 and CYP2D6 isoenzymes. Subject age, gender, and race can play a key role in inter-subject variability in pharmacokinetics and thus efficacy and safety of drugs. This article examines the effects of age, gender, and race on the pharmacokinetics and pharmacodynamics of fesoterodine.
Methods: Data from two randomized, double-blind, placebo-controlled, parallel-group trials in healthy subjects are presented: Study 1 investigated the effects of race (white vs. black men) and Study 2 investigated the effects of age (young vs. old men) and gender (elderly men vs. elderly women) on the pharmacokinetics and pharmacodynamics of single doses of fesoterodine 8 mg. In both studies, the primary endpoints were area under the concentration-time curve up to the last sample (AUC0-tz) and maximum concentration (Cmax) of 5-HMT in plasma. Pharmacodynamic variables included spontaneous salivary secretion (Studies 1 and 2) and residual urine volume (Study 2 only). The two studies included 5 groups of 16 subjects each (randomized 3 : 1 to fesoterodine or placebo): white men aged 18 - 45 years, black men aged 18 - 45 years (Study 1); young white men aged 18 - 40 years, elderly white men aged > 65 years, and elderly white women aged > 65 years (Study 2).
Results: There were no clinically meaningful differences in the primary endpoints between white and black subjects or between young white men, elderly white men, and elderly white women. Mean AUC0-tz was 70.7 ng/ml x h in whites and 64.1 ng/ml x h in blacks; mean Cmax was 6.1 and 5.5 ng/ml in whites and blacks, respectively. Mean AUC0-tz in young white men, elderly white men, and elderly white women was 49, 48, and 54 ng/ml x h, respectively; mean Cmax in young white men, elderly white men, and elderly white women was 4.1, 3.8, and 4.6 ng/ml, respectively. Consistent with the anticholinergic pharmacology of fesoterodine, declines in salivary volume were observed in both studies, and elevations in residual urinary volume were observed, especially in elderly subjects, in Study 2. Fesoterodine was well tolerated, with common adverse events such as headache and dry mouth recognized as antimuscarinic class effects.
Conclusions: Subject demographics, such as age, gender, and race, do not have a clinically meaningful effect on 5-HMT pharmacokinetics or pharmacodynamics after single-dose administration of fesoterodine 8 mg; thus, no dosage adjustment is required for fesoterodine based on age, gender, or race.