The manufacturers say that the concurrent use of
leflunomide and
azathioprine has not yet been studied but it would be expected to increase the risk of serious adverse reactions (haematological
toxicity or hepatotoxicity).
Azathioprine is rapidly and extensively metabolised to mercaptopurine. Mercaptopurine is therefore expected to interact similarly.
The manufacturers advise avoiding concurrent use. As the active
metabolite of
leflunomide has a long
half-life of 1 to 4 weeks, a washout with colestyramine or activated charcoal should be given if patients are to be switched to other DMARDs.