Increased exposure w/ potent CYP2D6 inhibitors eg, paroxetine, terbinafine, cimetidine, quinidine; potent CYP3A4 inhibitors eg, PIs, ketoconazole, itraconazole; potent P-gp inhibitors eg, cyclosporine, verapamil; moderate CYP3A4 inhibitors eg, erythromycin, clarithromycin, telithromycin, fluconazole, grapefruit juice. Decreased plasma conc w/ CYP3A4 inducers eg, rifampicin, carbamazepine, barbiturates, St. John's wort. Increased exposure of CYP2D6 substrates eg, flecainide, thioridazine, TCAs (eg, imipramine). Modest increase in midazolam (CYP3A4 substrate) exposure. Small increase in digoxin exposure. More pronounced therapeutic & side effects w/ medicinal products that possess antimuscarinic properties eg, oxybutynin, tolterodine, flavoxate. Potentiation of anticholinergic effects w/ anti-parkinson agents & TCAs.