Paroxetine increases the AUC of
darifenacin by a modest 33%.
Terbinafine is predicted
to interact similarly (both
paroxetine and
terbinafine are CYP2D6 inhibitors). However, these changes seem unlikely to be clinically relevant.
No dosage adjustments are recommended by the US manufacturer. The UK manufacturer recommends that the dose of
darifenacin should be started at 7.5 mg daily and, if well tolerated, titrated to 15 mg. This seems a cautious approach. Bear in mind the possibility of an interaction if antimuscarinic effects (dry mouth, constipation, drowsiness) are increased.