Ketoconazole increases
solifenacin levels 2- to 3-fold by inhibiting CYP3A4. The manufacturers say other potent CYP3A4 inhibitors (such as the
protease inhibitors) will have the same effect.
The manufacturers limit the daily dose of
solifenacin to 5 mg if it is given with potent inhibitors of CYP3A4. In addition, in patients with severe
renal impairment or moderate
hepatic impairment, concurrent use is contraindicated.