Several large-scale clinical trials have shown that long-term use of antimuscarinic agents for overactive bladder treatment increases the risk of dementia and that this risk varies between agents. Fesoterodine, an overactive bladder antimuscarinic, reportedly has no significant effect on cognitive function. Differences in the brain distribution of antimuscarinic agents and blockade of muscarinic receptors could be the reasons for the differences in central side effects among antimuscarinics. In this study, we assessed the brain distribution of antimuscarinic agents and muscarinic receptor occupancy using brain microdialysis and in vivo receptor-binding analysis in rats. The test drugs were 5-hydroxymethyl tolterodine (5-HMT), an active metabolite of fesoterodine, oxybutynin, and trihexyphenidyl, a central antimuscarinic agent. The brain/plasma unbound concentration ratio at steady state (K