Drug Interactions between atrasentan and dexamethasone / moxifloxacin

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.

GENERALLY AVOID: Coadministration with potent or moderate inducers of CYP450 3A4 may significantly decrease the plasma concentrations of atrasentan, which is primarily metabolized by the isoenzyme. In drug interaction studies, coadministration with the potent CYP450 3A4 inducer rifampin reduced atrasentan (single dose, 10 mg) trough plasma concentration (Ctrough) by 90%. Rifampin is also an inhibitor of the hepatic influx transporters organic anion transporting polypeptides (OATP) 1B1 and 1B3, of which atrasentan is a substrate. No data are available about potent or moderate CYP450 3A4 inducers that do not inhibit OATP1B1 and/or 1B3, but greater decreases in atrasentan exposure may occur.

MANAGEMENT: Concomitant use of atrasentan with potent or moderate CYP450 3A4 inducers should generally be avoided.