Evaluation of 2 Trilostane Protocols for the Treatment of Canine Pituitary-Dependent Hyperadrenocorticism: Twice Daily versus Once Daily

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.

Serum Bile Acids Concentrations and Liver Enzyme Activities after Low-Dose Trilostane in Dogs with Hyperadrenocorticism

Hyperadrenocorticism (HAC) often leads to vacuolar hepatopathy. The impact of trilostane treatment on serum total bile acids (SBAs) concentrations in dogs with HAC remains unknown. This study investigated SBAs concentrations in healthy dogs and those with HAC following trilostane therapy. Ten healthy dogs and fifteen dogs with HAC were prospectively enrolled. A biochemistry profile and pre- and post-prandial SBAs concentrations were determined in each dog. Dogs with HAC were reassessed at 1 and 3 months after the initiation of trilostane treatment. Dogs with HAC had significantly higher serum ALT, ALP, and GGT activities, and cholesterol, triglyceride, and pre-prandial SBAs concentrations compared to healthy dogs. After 3 months of trilostane treatment, polyuria/polydipsia and polyphagia were completely resolved in 42.8% and 35.7%, respectively. Significant improvements in serum ALT and ALP activities and cholesterol concentrations were observed within 1-3 months of trilostane treatment. However, pre- and post-prandial SBAs concentrations did not significantly decrease. These findings suggest that treatment with low-dose trilostane for 3 months appears to reduce serum liver enzyme activities, but not SBAs concentrations. Further investigation is warranted to explore the effects of low-dose trilostane treatment on SBAs concentrations for a longer duration or after achieving appropriate post-ACTH cortisol levels.

Survival of dogs with pituitary-dependent hyperadrenocorticism treated twice daily with low doses of trilostane

BACKGROUND

Twice daily low trilostane doses have proven to be effective to manage canine Cushing's syndrome. However, survival and prognostic factors in dogs treated with this protocol have not been evaluated. The aim of the study was to evaluate survival and prognostic factors, including systolic blood pressure (SBP) at diagnosis, in dogs with pituitary-dependent hypercortisolism (PDH) treated with low trilostane doses.

METHODS

Medical records of 91 dogs newly diagnosed with PDH initially treated with 0.2-1.1 mg/kg of trilostane twice daily were retrospectively included. Survival times were calculated using the Kaplan-Meier estimator. Univariable and multivariable analysis were performed using the Cox proportional hazard regression analysis.

RESULTS

Overall, median survival was 998 days (range 26-1832 days, 95% confidence interval = 755-1241 days). In the multivariable analysis, age (hazard ratio [HR] = 1.337, p < 0.001), presence of calcinosis cutis (HR = 5.271, p < 0.001), body condition score (BCS) ≤3/9 (HR = 8.100, p < 0.001) and higher platelet count (HR = 1.002, p = 0.022) were negatively correlated with survival. SBP was not associated with survival.

CONCLUSIONS

Low-dose trilostane treatment twice daily provides slightly longer survival than previously reported for dogs with PDH treated once or twice daily at higher doses. Older age, presence of calcinosis cutis, low BCS and higher platelet count, but not systemic hypertension, are predictive of poorer prognosis in dogs with PDH.

Association between ACTH stimulation test results and clinical signs in dogs with hyperadrenocorticism treated with trilostane

Trilostane is the recommended medical treatment for dogs with hyperadrenocorticicm (HAC). The objective of this study was to investigate the association between ACTH stimulation test (ACTHST) results, and relevant clinical signs, in dogs treated with trilostane. A disease-specific questionnaire was developed, which included the owner's assessment of polydipsia, polyuria, polyphagia, panting, and satisfaction with the treatment, based on a 5-response category rating scale. Forty-nine dogs with HAC were prospectively enrolled. Dogs were grouped according to their recheck appointment (first recheck, 710 days after commencement of treatment or change of trilostane dose; second recheck, 4 weeks after the first recheck; third recheck, performed at 3-6 months intervals once the dog was well controlled). At the recheck appointment, the owner's questionnaire responses were recorded, and an ACTHST was performed, along with urine specific gravity measurement. Linear mixed effects models were used to assess differences among the three recheck time points and to test possible associations between ACTHST results and clinical signs. Significant differences between rechecks were present for stimulated cortisol (first to third recheck, P < 0.001; second to third recheck, P < 0.01), polydipsia (first to second recheck, P = 0.001), polyuria (first to second recheck, P < 0.001; first to third recheck, P = 0.001), and owner satisfaction (first to second recheck, P < 0.001; first to third recheck, P < 0.001). Backward stepwise variable elimination did not identify any significant associations between ACTHST results and clinical signs. Therefore, clinical signs of HAC were not predicted based on the ACTHST results.

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

This study aimed to retrospectively describe the clinical progression following diagnosis of iatrogenic hypocortisolemia (iHC) in 48 dogs receiving trilostane for pituitary-dependent hyperadrenocorticism. Cortisol concentrations were ≥1.5 mg/dL within 6 mo following diagnosis of iHC in 76.3% of dogs (95% confidence interval [CI] 59.8-88.6%). At the time of study completion, 25% of dogs (95% CI 13.6-39.6%) were receiving either glucocorticoids or mineralocorticoids or both; 42% of dogs (95% CI 27.6-56.8%) were on no adrenal-related medications; and the remaining 33% of dogs (95% CI 20.4-48.4%) were receiving trilostane. No patient-, clinicopathologic-, or trilostane-associated factors were identified to influence adrenal recovery following diagnosis of iHC, and it remains difficult to predict the clinical progression in this population of dogs.

Treating canine Cushing's syndrome: Current options and future prospects

Naturally occurring hypercortisolism, also known as Cushing's syndrome, is a common endocrine disorder in dogs that can be caused by an adenocorticotrophic hormone (ACTH)-producing pituitary adenoma (pituitary-dependent hypercortisolism, PDH; 80-85% of cases), or by an adrenocortical tumor (ACT; 15-20% of cases). To determine the optimal treatment strategy, differentiating between these two main causes is essential. Good treatment options are surgical removal of the causal tumor, i.e. hypophysectomy for PDH and adrenalectomy for an ACT, or radiotherapy in cases with PDH. Because these options are not without risks, not widely available and not suitable for every patient, pharmacotherapy is often used. In cases with PDH, the steroidogenesis inhibitor trilostane is most often used. In cases with an ACT, either trilostane or the adrenocorticolytic drug mitotane can be used. Although mostly effective, both treatments have disadvantages. This review discusses the current treatment options for canine hypercortisolism, and considers their mechanism of action, efficacy, adverse effects, and effect on survival. In addition, developments in both adrenal-targeting and pituitary-targeting drugs that have the potential to become future treatment options are discussed, as a more selective and preferably also tumor-targeted approach could have many advantages for both PDH and ACTs.

From Oxiranes to Oligomers: Architectures of U.S. FDA Approved Pharmaceuticals Containing Oxygen Heterocycles

Oxygen heterocycles are the second most common type of heterocycles that appear as structural components of U.S. Food and Drug Administration (FDA) approved pharmaceuticals. Analysis of our database of drugs approved through 2017 reveals 311 distinct pharmaceuticals containing at least one oxygen heterocycle. Most prevalent among these are pyranoses, with furanoses, macrolactones, morpholines, and dioxolanes rounding off the top five. The main body of this Perspective is organized according to ring size, commencing with three- and four-membered rings and ending with macrocycles, polymers, and unusual oxygen-containing heterocycles. For each section, all oxygen heterocycle-containing drugs are presented along with a brief discussion about structural and drug application patterns.

Effect of Intravenous or Perivascular Injection of Synthetic Adrenocorticotropic Hormone on Stimulation Test Results in Dogs

Background

Standard protocols for adrenocorticotropic hormone (ACTH) stimulation testing (ACTHst) often involve intravenous (IV) injection of corticotropin. ACTH might be unintentionally injected into the perivascular (PV) space.

Objective

To compare stimulation test results after IV and PV injections of ACTH.

Animals

Twenty privately owned dogs were studied: 10 healthy and 10 with trilostane‐treated naturally occurring hyperadrenocorticism (HAC).

Methods

Prospective study. Each of 20 dogs underwent 2 ACTHst not <4 nor more than 14 days apart. Five healthy and 5 HAC dogs had an IV ACTHst first and PV second; 5 healthy and 5 HAC dogs had a PV ACTHst first and IV second. Blood samples for measurement of serum cortisol concentration were collected before and 1 hour after ACTH administration.

Results

No significant difference in results was demonstrated when comparing serum cortisol concentrations after IV and PV ACTH administration in all 20 dogs (median μg/dL; interval μg/dL: 8.2; 1.4–17.4 versus 7.8; 0.9–16.9; P = .23). No significant difference in results was demonstrated when comparing serum cortisol concentrations after IV and PV ACTH administration in the 10 healthy dogs (median μg/dL; interval μg/dL: 10.9; 7.3–17.4 versus 10.6; 7.1–16.9; P = .54) or in the 10 HAC dogs (median μg/dL; interval μg/dL: 6.3; 1.4–8.6 versus 5.2; 0.9–8.7; P = .061).

Conclusions and Clinical Importance

Perivascular administration of ACTH does not significantly alter stimulation test results in healthy dogs or in dogs with HAC undergoing therapy with trilostane.

Clinical Relationship between Cholestatic Disease and Pituitary-Dependent Hyperadrenocorticism in Dogs: A Retrospective Case Series

Background

A high prevalence of cholestatic disease, including gallbladder mucocele (GBM), has been reported in dogs with naturally occurring pituitary‐dependent hyperadrenocorticism (PDH).

Hypothesis/Objectives

Differences exist in the clinical features of dogs with PDH and concurrent cholestatic disease, and also is the management of these dogs with trilostane.

Animals

Sixty‐five client‐owned dogs with naturally occurring PDH.

Methods

This was a retrospective, observational case series. Each dog was treated with trilostane for at least 3 months before the study, and had a good clinical response, as determined by owners. Statistical comparisons of clinical signs, results of routine blood tests, basal and post‐ACTH cortisol concentration, and optimal trilostane dosage were made after dogs were separated into the following 3 groups by ultrasonographic imaging: normal on ultrasound (NOU) group, cholestasis group, and GBM group.

Results

The GBM group had more severe clinical signs and significantly different total serum cholesterol concentration and post‐ACTH stimulation cortisol concentration at the time of diagnosis. Dogs that weighed <6 kg had a significantly higher prevalence of cholestatic disease than did the other dogs (P = .003). The optimal trilostane dosages for the GBM and cholestasis groups were 2.5 and 1.5 times the dosage of the NOU group, respectively (P < .001).

Conclusions and Clinical Importance

Gallbladder disease associated with cholestatic disease is correlated with PDH in dogs, in both its clinical features and drug management. These findings may be associated with hypercholesterolemia, unidentified genetic factors, and the hydrophobic nature of trilostane.

Comparison of Survival Times for Dogs with Pituitary-Dependent Hyperadrenocorticism in a Primary-Care Hospital: Treated with Trilostane versus Untreated

Background

Although pituitary‐dependent hyperadrenocorticism (PDH) is one of the most common endocrinopathies in dogs, the effects of withholding treatment on survival time in dogs with PDH remain unclear.

Hypothesis/Objectives

The purpose of this study was to clarify the effects of treatment in dogs with PDH by comparing survival times between dogs treated with trilostane and untreated dogs.

Animals

Forty‐three dogs diagnosed with PDH at a primary‐care hospital in Japan between June 2009 and January 2014.

Methods

Retrospective cohort study. The medical records of dogs with PDH treated with trilostane (n = 17) or left untreated (n = 26) were reviewed retrospectively. Survival analysis at 2 years after diagnosis of PDH was performed.

Results

Median survival time for the trilostane group was not reached (95% confidence interval [CI], 443 days–not applicable) and was significantly longer than the 506 days (95% CI, 292–564 days; P = .016) for the untreated group. Multivariate Cox proportional hazards analysis (including age at diagnosis, basal cortisol concentration at diagnosis, and treatment group) only identified assignment to the untreated group (hazard ratio, 5.01; 95% CI, 1.63–15.44) as associated with increased mortality.

Conclusions and Clinical Importance

The results of this retrospective cohort study suggest that withholding treatment for dogs with PDH might be associated with a higher risk of death. This represents the largest study to date to report survival times of untreated dogs with PDH.

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.

Prognostic factors for survival in dogs with pituitary-dependent hypercortisolism treated with trilostane

Pituitary-dependent hypercortisolism (PDH) is one of the most frequent endocrinopathies in dogs, but prognostic factors are largely unknown. The aim of this retrospective case series study was to determine the prognostic value of different clinical and clinicopathological variables evaluated in dogs newly diagnosed with PDH that were subsequently treated with trilostane. Medical records from one referral centre were evaluated. Eighty-five dogs with PDH were included. The median survival time was 852 days (range 2-3210 days); 60/85 (70 per cent) and 25/85 (29 per cent) dogs survived more than one and three years, respectively. In multivariable model analysis the length of survival of older dogs (HR 1.24, 95% CI 1.09 to 1.40) and dogs with higher serum phosphate concentrations (HR 1.35, 95% CI 1.01 to 1.81) was shorter. Serum phosphate concentrations were above the reference range in 37/85 (44 per cent) of animals. Clinical signs, liver enzymes, serum cortisol concentrations of the endocrine tests, proteinuria, systolic hypertension, the presence of concomitant disorders, and the frequency of trilostane administration were not associated with survival time. Hyperphosphataemia is a common finding in dogs with newly diagnosed PDH and represents a negative prognostic factor.