Results of clinical examinations, laboratory tests, and ultrasonography in dogs with pituitary-dependent hyperadrenocorticism treated with trilostane.

Objective: To determine the efficacy of trilostane, a 3beta-hydroxysteroid dehydrogenase inhibitor, in dogs with pituitary-dependent hyperadrenocorticism (PDH).
Animals: 11 dogs with PDH.
Procedure: The initial dose of trilostane was 30 mg, PO, q 24 h for dogs that weighed < 5 kg and 60 mg, PO, q 24 h for dogs that weighed > or = 5 kg. A CBC count, serum biochemical analyses, urinalysis, ACTH stimulation test, and ultrasonographic evaluation of the adrenal glands were performed in each dog 1, 3 to 4, 6 to 7, 12 to 16, and 24 to 28 weeks after initiation of treatment.
Results: All dogs responded well to treatment. All had reductions in polyuria-polydipsia and panting and an increase in activity. Polyphagia decreased in 9 of 10 dogs, and 9 of 11 dogs had improvement of coat quality and skin condition. Concentration of cortisol after ACTH stimulation significantly decreased by 1 week after initiation of treatment. After treatment for 6 months, clinical signs resolved in 9 dogs. In the other 2 dogs, marked clinical improvement was reported for 1 dog, and moderate improvement was reported in the other dog. Ultrasonographically, there was a considerable change in the parenchyma and an increase in size of the adrenal glands. Adverse effects consisted of 1 dog with transient lethargy and 1 dog with anorexia.
Conclusions and Clinical Relevance: Trilostane is an efficacious and safe medication for treatment of dogs with PDH. Additional studies in a larger group of dogs and characterization of progressive changes in adrenal glands are needed.