Desfesoterodine is an active metabolite of antimuscarinic drugs for the treatment of overactive bladder fesoterodine and tolterodine. In contrast to the cytochrome P450 (CYP) 2D6-mediated metabolism of tolterodine, desfesoterodine formation from fesoterodine occurs via ubiquitous nonspecific esterases. Serum levels of the desfesoterodine in humans are generally comparable to those of tolterodine following oral administration of the parent compound. The pharmacological in vitro and in vivo profiles of desfesoterodine are almost identical to those of tolterodin. The potent antimuscarinic action of desfesoterodine on the urinary bladder was confirmed in the in vivo studies and, like tolterodine, desfesoterodine was significantly more potent in inhibiting bladder contractions than salivation in the anaesthetised cat. Desfesoterodine is more potent than tolterodine in vivo. The apparent difference in potency in vivo might be explained by the degree of serum protein binding of the two compounds. The fraction of unbound drug in serum is larger for desfesoterodine than for tolterodine. Desfesoterodine may contribute to the therapeutical action of tolterodine.