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CYP3A4 Inhibitors: The systemic exposure of Darifenacin is increased with concomitant use of CYP3A4 Inhibitors. The dose should not exceed 7.5 mg daily when co-administered with potent CYP3A4 inhibitors (e.g. ketoconazole, itraconazole, ritonavir, nelfinavir, clarithromycin, and nefazadone). No dosage adjustment is required if co-administered with moderate CYP3A4 inhibitors (erythromycin, fluconazole, diltiazem, and verapamil).
CYP2D6 Inhibitors: No dosing adjustment needed in the presence of CYP2D6 inhibitors (paroxetine, fluoxetine, quinidine, and duloxetine).
CYP2D6 Substrates: Caution should be taken when used concomitantly with drugs that are predominantly metabolized by CYP2D6 as they have a narrow therapeutic index (flecainide, thioridazine, and TCAs).
CYP3A4 Substrates: Darifenacin (30 mg daily) has no significant impact on the pharmacokinetics of Midazolam (7.5 mg).
Oral Contraceptives: Darifenacin (10 mg three times daily) had no effect on the pharmacokinetics of the combination oral contraceptives containing levonorgestrel and ethinyl estradiol.
Warfarin: Standard therapeutic prothrombin time monitoring for warfarin should be continued. The effect of warfarin on prothrombin time was not altered when co-administered with darifenacin.
Digoxin: Darifenacin (30 mg daily) did not have a clinically relevant effect on the pharmacokinetics of digoxin (0.25 mg) at steady-state. Routine therapeutic drug monitoring for digoxin should be continued.
Other Anticholinergic Agents: Anticholinergic Agents may potentially alter the absorption of some concomitantly administered drugs due to effects on gastrointestinal motility. Concomitant use of Darifenacin with other anticholinergic agents may increase the frequency and/or severity of dry mouth, constipation, blurred vision, and other anticholinergic pharmacological effects.
