Comparison of Factors that Influence Survival in Dogs with Adrenal-Dependent Hyperadrenocorticism Treated with Mitotane or Trilostane

Background: Trilostane is a recognized treatment for canine pituitary-dependent hyperadrenocorticism (PDH); however, its efficacy in dogs with adrenal-dependent hyperadrenocorticism (ADH) is unknown. Objectives: To examine factors that might influence survival in the medical management of ADH, with particular emphasis on treatment selection. Animals: Thirty-seven animals referred to 4 centers over a period of 12 years that had been diagnosed with ADH and treated with either trilostane (22/37), mitotane (13/37), or both (2/37). Methods: Retrospective analysis of clinical records. Results: There was no statistically significant difference between the survival times of 13 dogs treated only with mitotane when compared with 22 dogs treated only with trilostane. The median survival time for animals treated with trilostane was 353 days (95% confidence interval [CI] 95–528 days), whereas it was 102 days (95% CI 43–277 days) for mitotane. Metastatic disease was detected in 8 of 37 dogs. There was a significantly lower probability of survival for dogs with metastatic disease when compared with those without metastatic disease (P < .001). Conclusions and Clinical Importance: The choice of medical treatment for ADH may not have a major effect on survival times. However, the presence of metastatic disease considerably decreases survival time regardless of the choice of medical treatment.