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Pharmacokinetic profile of fesoterodine.

OBJECTIVE
Fesoterodine is a new antimuscarinic agent for the treatment of overactive bladder. Following oral administration, fesoterodine is rapidly and extensively hydrolyzed by nonspecific esterases to its active moiety: 5-hydroxymethyl tolterodine (5-HMT). The cytochrome P450 (CYP) enzymes are not involved in the formation of 5-HMT; however, CYP2D6 and CYP3A4 provide 2 alternative pathways for further metabolism and inactivation of 5-HMT.


MATERIALS
Single oral doses of 4 mg, 8 mg or 12 mg of fesoterodine sustained-release tablets in the fasted state and 8 mg in a fed state.


METHODS
This single-center, open-label, randomized, crossover study investigated the effects of fesoterodine in healthy volunteers comprised of CYP2D6 extensive metabolizers (EMs; n = 16) and CYP2D6 poor metabolizers (PMs; n = 8) after either an overnight fast or a high-fat and high-calorie breakfast. Adverse events, vital signs, ECG recordings and laboratory tests were monitored for safety assessment.


RESULTS
For the principal active moiety, 5-HMT, the maximum plasma concentration (Cmax), area under the concentration-time curve from time zero to time of last measurable concentration (AUC0-t) and amount excreted in urine (Ae) increased proportionally with dose in both EM and PM subjects. The mean Cmax and AUC0-t in PMs were approximately twice those observed in EMs. CYP2D6 status had no effect on time to reach Cmax (5 h), renal clearance (approximately 250 ml/min), or half-life (approximately 8 h). Fesoterodine was well tolerated at all doses. While the incidence of dry mouth increased from 8 - 12 mg, all occurrences were mild-to-moderate.


CONCLUSIONS
Fesoterodine demonstrated a pharmacokinetic (PK) profile that was favorable for once-daily dosing. The systemic exposure to 5-HMT increased proportionally with dose and was about 2-fold higher in PMs compared with EMs. There was no clinically relevant effect of food on the PK of fesoterodine. Fesoterodine was well tolerated at all dose levels studied.