Drug Interaction Report

CONTRAINDICATED: Coadministration with febuxostat may significantly increase the plasma concentrations of xanthine oxidase substrates such as azathioprine, mercaptopurine, and theophylline. Toxicity may result. The proposed mechanism is inhibition of xanthine oxidase by febuxostat. Although drug interaction studies have not been conducted with febuxostat and xanthine oxidase substrates, the interaction has been reported with allopurinol, another xanthine oxidase inhibitor. Severe bone marrow suppression and other toxicities have been associated with concomitant use of allopurinol and mercaptopurine (6-MP) or azathioprine. Increased theophylline concentrations have also been reported during coadministration with allopurinol at dosages of 600 mg/day or greater.

MANAGEMENT: The use of febuxostat in patients treated with azathioprine, mercaptopurine, or theophylline is considered contraindicated.