Treatment with Leflunomide in Conjunction with Glucocorticoids for Dogs with Immune-Mediated Polyarthritis Is Not Associated with Improved Outcomes: A Retrospective Cohort Study of 93 Dogs from Australia (2017-2024).

Immune-mediated polyarthritis (IMPA) has a relatively high relapse rate compared to other immune-mediated diseases. Leflunomide is frequently used to treat dogs with IMPA in conjunction with prednisolone. This retrospective cohort study aimed to evaluate the therapeutic efficacy of leflunomide as an adjunctive therapy to prednisolone in reducing relapse and mortality rates in dogs diagnosed with IMPA in Australia. The medical records of client-owned dogs diagnosed with IMPA at a specialist referral hospital in Southeast Queensland from 2017 to 2024 were reviewed. A total of 93 dogs were included in this study, divided into two groups based on the treatment received: Group PRED, consisting of 53 dogs treated with prednisolone as the sole immunosuppressive agent, and Group L+PRED, consisting of 40 dogs that received leflunomide as adjunctive therapy alongside prednisolone. Data collected included breed, age, weight, sex, serum C-reactive protein concentration, results of synovial fluid analysis and microbial culture, treatment protocol, relapse rates and time to relapse, and mortality rates. There was no difference in relapse or mortality rates, time to relapse, nor time to discontinue prednisolone between the PRED and L+PRED groups. The L+PRED group had higher body weights and lower prednisolone dose rate at discharge compared to those in the PRED group. This study demonstrated that the use of leflunomide as an adjunctive therapy to prednisolone for the treatment of dogs with IMPA had no improved outcomes, reduced relapse rates, or shortening in the duration of prednisolone therapy when compared to dogs receiving prednisolone monotherapy.