Comparative evaluation of central muscarinic receptor binding activity by oxybutynin, tolterodine and darifenacin used to treat overactive bladder.
The Journal of urology 2007 Feb 1; 177(2):766-70
Oki T, Kageyama A, Takagi Y, Uchida S, Yamada S
Department of Pharmacokinetics and Pharmacodynamics, University of Shizuoka, Suruga-ku, Shizuoka, Japan.
PURPOSE: We characterized muscarinic receptor binding in the mouse cerebral cortex after oral administration of anticholinergic agents used to treat overactive bladder. MATERIALS AND METHODS: Muscarinic receptors in the mouse cerebral cortex and bladder after oral administration of anticholinergic agents were measured using [(3)H]N-methylscopolamine. RESULTS: In vitro binding affinities of tolterodine and its metabolite 5-hydroxymethyl metabolite in the mouse cerebral cortex and bladder were considerably greater than those of oxybutynin and darifenacin. Also, muscarinic receptor binding affinity of oxybutynin and its metabolite N-desethyl-oxybutynin in the cerebral cortex compared with that in the bladder was 2 to 3 times higher, whereas that of tolterodine and 5-hydroxymethyl metabolite was approximately 2 times lower. Oral administration of oxybutynin (76.1 micromol/kg), tolterodine (6.31 micromol/kg) and darifenacin (59.1 micromol/kg) showed binding activity that was approximately equal to that of bladder muscarinic receptors. Oral administration of oxybutynin (76.1 micromol/kg) showed significant binding of cerebral cortical muscarinic receptors in mice, as indicated by about a 2-fold increase in K(d) values for specific [(3)H]N-methylscopolamine binding 0.5 and 2 hours later. On the other hand, tolterodine and darifenacin given at oral doses that would exert a similar extent of bladder receptor binding activity as oxybutynin showed only a low level of binding activity of central muscarinic receptors in mice. CONCLUSIONS: Significant binding of brain muscarinic receptors in mice was observed by the oral administration of oxybutynin but not tolterodine and darifenacin.