Tolterodine: selectivity for the urinary bladder over the eye (as measured by visual accommodation) in healthy...

Tolterodine exhibits a favourable selectivity for the urinary bladder over salivary glands in vivo, in the anaesthetised cat, whereas oxybutynin shows the opposite selectivity profile in this model. This study further evaluated the selectivity profiles of tolterodine and oxybutynin by comparing the effects on bladder function and visual accommodation in the same individuals.

In a double-blind, randomised, four-way crossover study, 16 healthy volunteers received single oral doses of tolterodine 5 mg and oxybutynin 2.5, 5 and 7.5 mg. Voiding parameters were assessed for 12 hours post-dose, along with visual accommodation (near point of vision) at regular intervals.

A dose-dependent increase in maximum bladder capacity was observed for oxybutynin [2.5 mg (+35%), 5 mg (+45%) and 7.5 mg (%)]. The effect of tolterodine 5 mg on bladder capacity was approximately twice (+93%) that seen after oxybutynin 5 mg and the onset of the effect was more rapid with tolterodine. Effects on visual accommodation were also dose-dependent for oxybutynin (maximum changes in near point of vision were 13%, 20% and 29%, respectively). The maximum change observed after tolterodine 5 mg was the same as after oxybutynin 5 mg (i.e. 20%).

Tolterodine seems to exhibit selectivity for the bladder over the eye. Therefore, these results suggest that the normal dosage of tolterodine (2 mg twice daily) may have less effect on visual accommodation than the equivalent dosage of oxybutynin (5 mg three times daily) in patients with an overactive bladder.