Altered pharmacokinetics w/ CYP2D6 & CYP3A4 inhibitors. Avoid potent P-gp inhibitors eg, ciclosporin, verapamil. Increased in steady-state AUC w/ ketoconazole. Increased exposure in subjects who are poor metabolisers. Increased AUC & C
max w/ concurrent erythromycin in subjects who are extensive metabolisers. Decreased plasma conc w/ CYP3A4 inducers eg, rifampicin, carbamazepine, barbiturates, St. John's wort. Higher mean C
max & AUC w/ cimetidine. Drugs w/ narrow therapeutic window eg, flecainide, thioridazine or TCAs eg, imipramine. Modest increased midazolam exposure. Monitor prothrombin time w/ warfarin. Small increased digoxin exposure. Increased frequency & severity of antimuscarinic pharmacological effects.
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