The manufacturers of
tolterodine warn that potent CYP3A4 inhibitors (they name
clarithromycin and erythromycin) increase the risk of
tolterodine toxicity. Other
macrolides may also interact, see
macrolides.
Based on the interactions of other CYP3A4 inhibitors with
tolterodine it may be prudent to monitor for adverse effects and to bear in mind the possibility of an interaction if antimuscarinic effects (dry mouth, constipation, drowsiness) are increased. However, note that the UK manufacturers advise avoiding concurrent use, whereas the US manufacturers suggest reducing the
tolterodine dose to 1 mg twice daily.