Long‐Term Survival of Dogs with Adrenal‐Dependent Hyperadrenocorticism: A Comparison between Mitotane and Twice Daily Trilostane Treatment

BACKGROUND: Treatment of adrenal‐dependent hyperadrenocorticism (ADH) involves either surgical resection of the adrenal tumor or medical therapy. For many years, mitotane has been considered the medical treatment of choice for dogs with ADH. OBJECTIVES: The aim of this study was to determine survival and prognostic factors for dogs with ADH treated with mitotane and trilostane. ANIMALS: Twenty‐six dogs with ADH were included in the study. METHODS: Fourteen dogs were treated with mitotane and 12 dogs were treated with trilostane. Medical records were reviewed. Epidemiologic factors, signalment, clinicopathologic abnormalities, endocrine test results, and treatment protocols were evaluated to identify potential predictive factors of overall survival time. RESULTS: Survival times of dogs treated with mitotane (median, 15.6 months) or trilostane (median, 14.0 months) were not significantly different. Using univariate analysis, age and postadrenocorticotropic hormone cortisol concentrations were inversely correlated with survival time. The multivariate model also identified weakness at presentation as a negative prognostic indicator. CONCLUSION AND CLINICAL IMPORTANCE: The type of medical treatment (mitotane versus trilostane) does not influence survival time in dogs with ADH; therefore, trilostane, a drug with less frequent and milder adverse effects, might be used as the primary medical treatment when adrenalectomy cannot be performed.