[Anticholinergics for overactive bladder: does subtype selectivity play a role?]

Anticholinergics act in the treatment of overactive bladder by blocking muscarinic receptors of which five subtypes exist. Their desired effects occur via M(3) receptors, but a role for M(2) receptors is being discussed. Adverse effects such as dry mouth and constipation occur also via M(3) receptors, but M(2) and M(1) receptors can mediate side effects in the heart or on cognitive function, respectively. Therefore, an M(3)-selective drug such as darifenacin could theoretically be less effective but also have fewer cardiac or central nervous side effects. However, the limited available clinical data do not support a smaller efficacy or better general tolerability. The lack of adverse effects on cognitive function is well documented for darifenacin, but it cannot yet be determined definitively whether this discriminates it from other modern anticholinergics.