Tolterodineinteractions

7. DRUG INTERACTIONS Potent CYP3A4 inhibitors: Coadministration may increase systemic exposure to tolterodine tartrate extended-release capsules. Reduce tolterodine tartrate extended-release capsules dose to 2 mg once daily. Other Anticholinergics (antimuscarinics): Concomitant use with other anticholinergic agents may increase the frequency and/or severity of dry mouth, constipation, blurred vision, and other anticholinergic pharmacological effects.

7.1 Potent CYP2D6

Inhibitors Fluoxetine, a potent inhibitor of CYP2D6 activity, significantly inhibited the metabolism of tolterodine immediate release in CYP2D6 extensive metabolizers, resulting in a 4.8-fold increase in tolterodine AUC. There was a 52% decrease in C max and a 20% decrease in AUC of 5-hydroxymethyl tolterodine (5-HMT), the pharmacologically active metabolite of tolterodine. The sums of unbound serum concentrations of tolterodine and 5-HMT are only 25% higher during the interaction. No dose adjustment is required when tolterodine and fluoxetine are co-administered.

7.2 Potent CYP3A4

Inhibitors Ketoconazole (200 mg daily), a potent CYP3A4 inhibitor, increased the mean C max and AUC of tolterodine by 2- and 2.5-fold, respectively in CYP2D6 poor metabolizers. For patients receiving ketoconazole or other potent CYP3A4 inhibitors such as itraconazole, clarithromycin or ritonavir, the recommended dose of tolterodine tartrate extended release capsules is 2 mg once daily.

7.3 Other interactions

No clinically relevant interactions have been observed when tolterodine was co-administered with warfarin, with a combined oral contraceptive drug containing ethinyl estradiol and levonorgestrel, or with diuretics.

7.4 Other drugs metabolized by

Cytochrome P450 Isoenzymes In vivo drug-interaction data show that tolterodine immediate release does not result in clinically relevant inhibition of CYP1A2, 2D6, 2C9, 2C19, or 3A4 as evidenced by lack of influence on the marker drugs caffeine, debrisoquine, S-warfarin, and omeprazole.

7.5 Drug-Laboratory-Test

Interactions Interactions between tolterodine and laboratory tests have not been studied.

7.6 Other Anticholinergics

The concomitant use of tolterodine tartrate extended-release capsules with other anticholinergic (antimuscarinic) agents may increase the frequency and/or severity of dry mouth, constipation, blurred vision, somnolence and other anticholienrgic pharmacological effects.