Leflunomide is best classified as which type of DMARD?

• A. Conventional synthetic DMARD (csDMARD)
• B. Biologic DMARD (bDMARD)
• C. Targeted synthetic DMARD (tsDMARD)
• D. Antimicrobial agent

Answer: (A)

Leflunomide is best classified as a conventional synthetic DMARD because it is a non-biologic, small-molecule drug used to modify disease activity in rheumatoid arthritis by inhibiting dihydroorotate dehydrogenase and blocking pyrimidine synthesis, which reduces lymphocyte proliferation. This places it in the conventional synthetic DMARD group, alongside drugs like methotrexate, sulfasalazine, and hydroxychloroquine. It is not a biologic DMARD, which are large protein therapies such as monoclonal antibodies or receptor fusion proteins, nor a targeted synthetic DMARD, which includes small-molecule agents like JAK inhibitors that specifically block intracellular signaling pathways.