Cortisol Concentrations in Well-Regulated Dogs with Hyperadrenocorticism Treated with Trilostane.

BACKGROUND: There are no clear treatment guidelines for dogs with clinically well-regulated hyperadrenocorticism in which serum cortisol concentrations before and after an ACTH stimulation test performed 3-6 hours after trilostane administration are < 2.0 µg/dL. OBJECTIVE: To determine if serum cortisol concentrations measured before (Pre1) and after (Post1) ACTH stimulation at 3-6 hours after trilostane administration are significantly lower than cortisol concentrations measured before (Pre2) and after (Post2) ACTH stimulation 9-12 hours after trilostane administration, in a specific population of dogs with clinically well-regulated hyperadrenocorticism and Pre1 and Post1 <2 µg/dL. ANIMALS: Thirteen client-owned dogs with clinically well-regulated hyperadrenocorticism and Pre1 and Post1 serum cortisol concentrations <2.0 µg/dL 3-6 hours after trilostane administration. METHODS: Prospective study. Dogs had a second ACTH stimulation test performed 9-12 hours after trilostane administration, on the same day of the first ACTH stimulation test. Cortisol concentrations before and after ACTH stimulation were compared using a paired t-test. RESULTS: Cortisol concentrations before (1.4 ± 0.3 µg/dL) and after the first stimulation (1.5 ± 0.3 µg/dL, mean ± SD) were significantly lower than cortisol concentration before the second stimulation (3.3 ± 1.6 µg/dL, P = .0012 each). Cortisol concentration before the first stimulation was also significantly lower than cortisol concentration after the second stimulation (5.3 ± 2.4 µg/dL, P = .0001). CONCLUSIONS AND CLINICAL IMPORTANCE: In dogs with clinically well-regulated, trilostane-treated, hyperadrenocorticism, and cortisol concentrations <2 µg/dL before and after the first stimulation, a second ACTH stimulation test performed 9-12 hours after treatment can result in higher cortisol concentrations that could support continued trilostane treatment.