Objective—To determine the efficacy of trilostane, a
3β-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 ≥ 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
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. (Am J Vet Res 2002;63:506–512).