Efficacy of leflunomide for treatment of immune-mediated polyarthritis in dogs: 14 cases (2006-2008). Department of Surgical Sciences, School of Veterinary Medicine, University of Wisconsin, Madison, WI 53706, USA. colopys@svm.vetmed.wisc.edu JAVMA 2010 Feb 1 236 3 312-8 OBJECTIVE: To evaluate efficacy and adverse effects of leflunomide for the treatment of naturally occurring immune-mediated polyarthritis (IMPA) in dogs. DESIGN: Retrospective case series. ANIMALS: 14 dogs with cytologically confirmed IMPA. PROCEDURES: Medical records were used to identify dogs with a diagnosis of IMPA that were treated with leflunomide. Signalment, radiographic findings, laboratory data, dosage of leflunomide, treatment duration, treatment response, and occurrence of adverse effects were determined from medical records. RESULTS: Mean +/- SD initial dosage of leflunomide was 3.0 +/- 0.5 mg/kg (1.4 +/- 0.2 mg/lb) PO once daily. Treatment duration for the initial starting dosage ranged from 1 to 6 weeks. Of the 14 dogs treated with leflunomide, 8 had complete resolution of clinical signs of IMPA initially, 5 had partial response to treatment, and 1 had minimal response to treatment. Adverse effects from treatment with leflunomide were not observed during the treatment period. CONCLUSIONS AND CLINICAL RELEVANCE: Oral administration of leflunomide was a safe and effective alternative to oral administration of corticosteroids for treatment of IMPA in dogs. On the basis of findings in this study, a starting dosage for leflunomide of 3 to 4 mg/kg (1.4 to 1.8 mg/lb) PO once daily for at least 6 weeks before making dose adjustments is recommended. Dose adjustments should be based on cytologic evaluation of synovial fluid and clinical signs of IMPA. Hematologic variables, serum biochemical analysis results, and clinical signs of IMPA should be monitored for evidence of adverse effects to treatment with leflunomide.