Evaluation of Iatrogenic Hypocortisolemia Following Trilostane Therapy in 48 Dogs with Pituitary-Dependent Hyperadrenocorticism

Trilostane: Beyond Cushing's Syndrome

Trilostane is a drug able to block the synthesis of progesterone from pregnenolone, dependent on the enzyme 3β-hydroxysteroid dehydrogenase/Δ5-4 isomerase. As a consequence of this effect, it is used to treat endocrinological diseases such as Cushing's syndrome, especially in dogs. Because of the modulatory effects of trilostane on the hypothalamic-pituitary-adrenal axis, trilostane administration causes an increase in brain levels of neurosteroids with anticonvulsant properties, as in the case of allopregnanolone. Allopregnanolone is also of interest in curing depression, suggesting that trilostane might represent a tool to address neurological and psychiatric disorders. In this review, we investigated the historical development of this drug and its current use, mechanisms, and possible developments. By searching the literature from 1978 to 2025, we identified 101 papers describing studies with trilostane. Precisely, 55 were about dogs and trilostane, 3 were on cats, and 23 were with other animals. Some studies (15) were also designed with human patients. The main disease treatment with trilostane was hyperadrenocorticism. However, we also found two preclinical papers on trilostane's potential use in psychiatric diseases and three on trilostane's potential use in neurological disorders. Moreover, few clinical and preclinical studies suggested the involvement of neurosteroids modulated by trilostane in different neurological disorders, thus opening a possible new perspective for the use of this drug.

Iatrogenic symptomatic hypoadrenocorticism after treatment with trilostane for hyperadrenocorticism in dogs: eight cases (2008-2019)

OBJECTIVES

Trilostane is the medical treatment of choice for hyperadrenocorticism. Iatrogenic hypoadrenocorticism is thought to be rare, with most cases being transient and only a few cases of permanent hypoadrenocorticism have been reported. This study reports findings from eight cases of iatrogenic hypoadrenocorticism and examines the presence of concurrent diseases at the time of diagnosis.

MATERIALS AND METHODS

Medical records of dogs treated for hyperadrenocorticism with trilostane since 2008 were reviewed, and cases of clinical iatrogenic hypoadrenocorticism were extracted. Cases were considered permanent if long-term replacement therapy was required.

RESULTS

Eight dogs met the inclusion criteria. The time between the beginning of trilostane treatment and the diagnosis of hypoadrenocorticism ranged from 4 days to 13 months, and the dosage of trilostane ranged between 1 and 8 mg/kg/day. Six dogs had a suspicion of concurrent disease at the time of hypoadrenocorticism diagnosis. The trilostane dose was decreased in two dogs; trilostane was withdrawn in one case without further relapse of hyperadrenocorticism; and glucocorticoids with or without mineralocorticoid supplementation were prescribed in five dogs. Two of these five dogs were lost to follow-up, and the other three had a diagnosis of permanent hypoadrenocorticism. Adrenal gland ultrasonography in these three dogs showed a progressive reduction in gland sizes with heterogeneous echogenicity.

CLINICAL SIGNIFICANCE

Iatrogenic hypoadrenocorticism is a rare but potentially life-threatening complication of trilostane treatment in dogs with hyperadrenocorticism. The occurrence of a concurrent disease might trigger the development of clinical signs of hypoadrenocorticism in previously subclinical dogs.