Leflunomide-induced pneumonitis in a patient with rheumatoid arthritis

Intern Med. 2006;45(10):689-91. doi: 10.2169/internalmedicine.45.1455. Epub 2006 Jun 15.


Leflunomide is a disease-modifying antirheumatic drug (DMARD) that has been available in Japan since August 2003. Leflunomide-induced interstitial pneumonitis has not been reported as an adverse effect in other countries. We report a suspected case of leflunomide-induced interstitial pneumonitis. A 77-year-old woman with rheumatoid arthritis and a history of methotrexate-induced pneumonitis developed sudden-onset dyspnea on exertion about 2 months after the administration of leflunomide. She maintained a high concentration of an active metabolite of leflunomide for more than 3 weeks after withdrawal of the drug. She did not respond to treatment and died. Leflunomide must be administered with caution to patients with a history of interstitial pneumonitis or drug-induced pneumonitis. If leflunomide-induced pneumonitis is suspected, the plasma concentration must be immediately checked, along with elimination and withdrawal of the medication.

Publication types

  • Case Reports

MeSH terms

  • Adjuvants, Immunologic / adverse effects*
  • Aged
  • Arthritis, Rheumatoid / drug therapy*
  • Female
  • Humans
  • Isoxazoles / adverse effects*
  • Isoxazoles / therapeutic use
  • Leflunomide
  • Lung / diagnostic imaging
  • Lung / pathology
  • Pneumonia / chemically induced*
  • Pneumonia / diagnostic imaging
  • Pneumonia / pathology
  • Radiography
  • Radionuclide Imaging


  • Adjuvants, Immunologic
  • Isoxazoles
  • Leflunomide