BackgroundIdiopathic chronic hepatitis (CH) in dogs is a prevalent hepatic disorder. The etiology is poorly understood; however, there is evidence to support an immune-mediated pathogenesis. No literature exists investigating the efficacy of cyclosporine (CsA) therapy for CH in dogs.ObjectivesTo retrospectively evaluate the efficacy and adverse side effects of CsA in the treatment of CH in dogs, and to identify factors that impact response to CsA therapy.Animals48 client-owned dogs diagnosed with CH treated with CsA for at least 2 weeks.MethodsRetrospective review of medical records between the years 2010-2017.ResultsTwenty-two breeds of dogs were included of which 54% were spayed females, 42% neutered males and 4% intact males. Median age was 8.5 years (range, 0.7-14 years). Complete remission (normalization of alanine aminotransferase [ALT]) in response to CsA was attained in 79% of dogs (38/48). Median dose of CsA at the time of remission was 7.9 mg/kg/day (range, 2.5-12.7mg/kg/day) and median time to remission was 2.5 months (range, 0.75-18 months). None of the factors evaluated including clinical score, presence of ascites, hypoalbuminemia, hyperbilirubinemia, prolonged coagulation times, dose, or duration of therapy influenced remission. Common side effects were gastrointestinal signs in 38% (18/48) and gingival hyperplasia in 25% (12/48) of dogs.Conclusion and Clinical ImportanceCsA proved to be a tolerated and effective medication in attaining remission in dogs with idiopathic CH based on normalization of serum ALT. None of the evaluated factors were shown to negatively impact response to CsA or remission of disease.