Ketoconazole increases
solifenacin levels 2- to 3-fold by inhibiting CYP3A4. The manufacturers predict that other CYP3A4 inhibitors (e.g. itraconazole) will have the same effect.
It is recommended that only 5 mg of
solifenacin should be used in patients taking
itraconazole or
ketoconazole. The concurrent use of
solifenacin and these
azoles is contraindicated in patients with severe
renal impairment or moderate
hepatic impairment.