Drug Interactions between dexamethasone / moxifloxacin and fesoterodine

MONITOR CLOSELY: Concomitant administration of corticosteroids may potentiate the risk of tendinitis and tendon rupture associated with fluoroquinolone treatment. The mechanism is unknown. Tendinitis and tendon rupture have most frequently involved the Achilles tendon, although cases involving the rotator cuff (the shoulder), the hand, the biceps, and the thumb have also been reported. Some have required surgical repair or resulted in prolonged disability. Tendon rupture can occur during or up to several months after completion of fluoroquinolone therapy.

MANAGEMENT: Caution is recommended if fluoroquinolones are prescribed in combination with corticosteroids, particularly in patients with other concomitant risk factors (e.g., age over 60 years; recipient of kidney, heart, and/or lung transplant). Patients should be advised to stop taking the fluoroquinolone, avoid exercise and use of the affected area, and promptly contact their physician if they experience pain, swelling, or inflammation of a tendon. In general, fluoroquinolones should only be used to treat conditions that are proven or strongly suspected to be caused by bacteria and only if the benefits outweigh the risks.

MONITOR: Coadministration with inducers of CYP450 3A4 may decrease the plasma concentrations of fesoterodine's active metabolite, 5-hydroxymethyl tolterodine, which is partially metabolized by the isoenzyme. Following induction of CYP450 3A4 with rifampin 600 mg once a day, 5-hydroxymethyl tolterodine peak plasma concentration (Cmax) and systemic exposure (AUC) decreased by approximately 70% and 75%, respectively, after oral administration of fesoterodine 8 mg. The effects of less potent CYP450 3A4 inducers were not examined.

MANAGEMENT: Caution is advised when fesoterodine is used with CYP450 3A4 inducers. The possibility of diminished therapeutic effects should be considered.