Pharmacokinetics, safety, and efficacy of combination treatment with methotrexate and leflunomide in patients with active rheumatoid arthritis

Objective. To examine the safety and pharmacokinetics of and clinical response to leflunomide, a de novo pyrimidine synthesis inhibitor, when administered to patients with active rheumatoid arthritis (RA) who have been receiving long-term methotrexate therapy. Methods. This was an open-label, 52-week study in which 30 patients with RA that remained active despite therapy with methotrexate at 17 +/- 4 mg/week (mean +/- SD) for greater than or equal to 6 months were given leflunomide, 10-20 mg/day, Patients were assessed for adverse effects, pharmacokinetic measurements of leflunomide and methotrexate, and clinical response by American College of Rheumatology (ACR) 20% response criteria. Results. Twenty-three patients completed 1 year of treatment. No significant pharmacokinetic interactions between leflunomide and methotrexate were noted. This combination therapy was generally well tolerated clinically, with the exception of elevations of liver enzyme levels. Seven patients withdrew from the treatment regimen: 2 withdrawals were voluntary, 3 were due to persistent elevation of plasma transaminase levels, and 2 were due to lack of efficacy. Of the patients, 16 (53%) met ACR 20% response criteria. Two met ACR criteria for remission after 1 year. Conclusion. The combination of methotrexate and leflunomide has therapeutic potential in RA.