A Case of Interstitial Pneumonitis Caused by Leflunomide

Abstract

Leflunomide is a new disease modifying anti rheumatic drug (DMARD) for the treatment of active rheumatoid arthritis. Its mechanism of action differs from other DMARDs in that it inhibits the de novo pyrimidine synthesis by inhibiting dihydroorotate dehydrogenase and therefore prevents the proliferation of activated lymphocytes. As it has been prescribed worldwide, there is a great deal of much concerns regarding its potential adverse effects. Because leflunomide has an active metabolite with a long elimination half-life of approximately 2 weeks, serious adverse reactions may occur even after the leflunomide treatment has been stopped. The profile of serious reactions includes liver dysfunction, hematological disorders, severe skin reactions and respiratory dysfunction. Respiratory dysfunctions with leflunomide therapy are very rare and its incidence is lower than that of methotrexate therapy. However, there are reports in Japan showing that 5 patients died of interstitial pneumonitis and another 11 patients developed serious lung complications associated with leflunomide. This suggests the possibility of fatal respiratory toxicity of leflunomide. There are no reports of interstitial pneumonitis associated with leflunomide in Korea. We report a case of a 62-year old woman who developed interstitial pneumonitis, which might have been induced by leflunomide during the treatment of rheumatoid arthritis.