Evaluation of baseline cortisol, endogenous ACTH, and cortisol/ACTH ratio to monitor trilostane treatment in dogs with pituitary-dependent hypercortisolism

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.

Comparison of methods to monitor dogs with hypercortisolism treated with trilostane

Background

The use of adrenocorticotropic hormone stimulation test as method to monitor efficacy of trilostane treatment of hypercortisolism (HC) in dogs has been questioned.

Objectives

To evaluate and compare 12 methods with which to monitor efficacy of trilostane treatment in dogs with HC.

Animals

Forty‐five client‐owned dogs with HC treated with trilostane q12h.

Methods

Prospective cross‐sectional observational study. The dogs were categorized as well‐controlled, undercontrolled, and unwell through a clinical score obtained from an owner questionnaire. The ability to correctly identify trilostane‐treatment control of dogs with HC with the following variables was evaluated: before trilostane serum cortisol (prepill), before‐ACTH serum cortisol, post‐ACTH serum cortisol, plasma endogenous ACTH concentrations, prepill/eACTH ratio, serum haptoglobin (Hp) concentration, serum alanine aminotransferase (ALT), gamma‐glutamyl transferase (γGT) and alkaline phosphatase activity, urine specific gravity, and urinary cortisol : creatinine ratio.

Results

Ninety‐four re‐evaluations of 44 dogs were included; 5 re‐evaluations of 5 unwell dogs were excluded. Haptoglobin was significantly associated with the clinical score (P < .001) and in the receiver operating characteristic analysis, Hp cutoff of 151 mg/dL correctly identified 90.0% of well‐controlled dogs (specificity) and 65.6% of undercontrolled dogs (sensitivity). Alanine aminotransferase (P = .01) and γGT (P = .009) were significantly higher in undercontrolled dogs. Cutoff of ALT and γGT greater than or equal to 86 U/L and 5.8 U/L, respectively, were significantly associated with poor control of HC by trilostane.

Conclusions and Clinical Importance

Of all the 12 variables, Hp, and to a lesser degree ALT and γGT, could be considered additional tools to the clinical picture to identify well‐controlled and undercontrolled trilostane‐treated dogs.

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.

Laboratory assessment of trilostane treatment in dogs with pituitary-dependent hyperadrenocorticism

Background

Results of ACTH stimulation test (ACTHst), pre‐ and post‐trilostane serum cortisol concentrations (SCCs), urine concentration (urine‐specific gravity [USG]), and urine cortisol : creatinine ratios (UCCRs) are common variables used to monitor trilostane treatment of dogs with pituitary‐dependent hyperadrenocorticism (PDH). However, none has consistently discriminated dogs receiving an adequate dose (A) from those overdosed (O) or underdosed (U).

Objectives

To assess and compare recommended monitoring variables, including serial SCCs in a cohort of dogs with PDH treated with trilostane.

Animals

Privately owned dogs with PDH (n = 22) and 3 healthy dogs (controls).

Methods

Prospective, multicenter, 2‐day study. On day “a” (randomized): ACTHst was completed. Day “b” (>2 to <7 days later): SCCs were assessed −0.5 hours, immediately before, and 1, 2, 2.5, 3, 3.5, 4, 6, 8, and 12 hours after trilostane administration. On the first study day, urine collected at home was assessed for USG, UCCR and owner opinions regarding PDH were categorized as: A (clinical signs resolved), U (remains symptomatic), or ill (possible O).

Results

At 27 pairs of evaluations, 7 dogs were categorized as A, 19 U, and 1 possible O (excluded from the study). There was overlap in SCC results from the A and U dogs at every time point. Results of USG, UCCR, and ACTHst did not discriminate A from U dogs. Trilostane suppresses SCC within 1 hour of administration and its duration of action in most PDH dogs is <8 hours.

Conclusions and Clinical Importance

No single variable or group of variables reliably discriminated A dogs from U dogs during trilostane treatment for PDH.

Cushing's syndrome-an epidemiological study based on a canine population of 21,281 dogs

The epidemiological characteristics of spontaneous hypercortisolism (HC) were derived from 21,281 client-owned dogs selected from four private veterinary clinics and one university reference center for endocrinology. The odds ratio (OR) method was employed to investigate the risk of developing HC related to breed, gender, and sexual status. The estimated prevalence of HC in the four private clinics was 0.20% [95% confidence interval (CI), 0.13–0.27] and was significantly different compared to the university reference center (1.46%; 95% CI, 1.12–1.80). Sex, breed, and age resulted in risk factors for HC. Mean (± SD) age for dogs with HC was 9.8 (± 2.5) yr. Females had higher risk for HC compared to males (OR 1.85; 95% CI, 1.24–2.75); all neutered dogs (both males and females) had higher risk than intact dogs (OR 2.54; 95% CI, 1.72–3.73); and neutered females had higher risk compared to intact females (OR 2.61; 95% CI, 1.54–4.42). Using the mixed breed dogs as a control population (OR = 1), the risk of developing HC was significantly higher in the Standard Schnauzer (OR 58.1; p < 0.0001) and Fox Terrier (OR 20.33; p < 0.0001).

With regard to HC, this study identified an overall prevalence of 0.20%. The data support the existence of sex predisposition, with the highest risk for neutered females.

Comparison of two prepill cortisol concentrations in dogs with hypercortisolism treated with trilostane

Background

The ideal method for monitoring trilostane therapy in dogs with hypercortisolism is still open to debate. Recently, determination of the pre-trilostane (prepill) cortisol concentration has been proposed to be more repeatable than either post-trilostane or post-ACTH cortisol. The aim of this study was to compare two prepill cortisol concentrations in dogs with hypercortisolism during trilostane therapy. Sixteen client-owned dogs with naturally occurring hypercortisolism were prospectively included and cortisol concentrations were measured twice, 1 h apart, before the morning trilostane dose (prepill 1 and 2 cortisol).

Results

A total of 47 prepill cortisol measurement pairs were included. Compared to prepill 1, prepill 2 cortisol was higher in 15, equal in 8 and lower in 24 pairs. Group agreement between prepill 1 and 2 cortisol was 70% (moderate agreement - weighted kappa 0.55). In 30% of the pairs, group assignment was discrepant, implying a different therapeutic decision. In some dogs certain circumstances (e.g. excessive barking, difficulties during blood collection, excitement at arrival) were identified as potential factors explaining the discrepancy between prepill 1 and 2 cortisol measurements.

Conclusions

In a substantial number of dogs treated with trilostane, the two prepill cortisol concentrations differed. Part of this difference might be ascribable to stressful events during test performance. When using prepill cortisol measurements to monitor trilostane therapy, recording of any incident during handling that might affect cortisol release might be helpful to make a reliable decision about a trilostane dose adaptation.

ATR-101, a selective ACAT1 inhibitor, decreases ACTH-stimulated cortisol concentrations in dogs with naturally occurring Cushing's syndrome

BACKGROUND

Cushing's syndrome in humans shares many similarities with its counterpart in dogs in terms of etiology (pituitary versus adrenal causes), clinical signs, and pathophysiologic sequelae. In both species, treatment of pituitary- and adrenal-dependent disease is met with limitations. ATR-101, a selective inhibitor of ACAT1 (acyl coenzyme A:cholesterol acyltransferase 1), is a novel small molecule therapeutic currently in clinical development for the treatment of adrenocortical carcinoma, congenital adrenal hyperplasia, and Cushing's syndrome in humans. Previous studies in healthy dogs have shown that ATR-101 treatment led to rapid, dose-dependent decreases in adrenocorticotropic hormone (ACTH) stimulated cortisol levels. The purpose of this clinical study was to investigate the effects of ATR-101 in dogs with Cushing's syndrome.

METHODS

ATR-101 pharmacokinetics and activity were assessed in 10 dogs with naturally-occurring Cushing's syndrome, including 7 dogs with pituitary-dependent disease and 3 dogs with adrenal-dependent disease. ATR-101 was administered at 3 mg/kg PO once daily for one week, followed by 30 mg/kg PO once daily for one (n = 4) or three (n = 6) weeks. Clinical, biochemical, adrenal hormonal, and pharmacokinetic data were obtained weekly for study duration.

RESULTS

ATR-101 exposure increased with increasing dose. ACTH-stimulated cortisol concentrations, the primary endpoint for the study, were significantly decreased with responders (9 of 10 dogs) experiencing a mean ± standard deviation reduction in cortisol levels of 50 ± 17% at study completion. Decreases in pre-ACTH-stimulated cortisol concentrations were observed in some dogs although overall changes in pre-ACTH cortisol concentrations were not significant. The compound was well-tolerated and no serious drug-related adverse effects were reported.

CONCLUSIONS

This study highlights the potential utility of naturally occurring canine Cushing's syndrome as a model for human disease and provides proof of concept for ATR-101 as a novel agent for the treatment of endocrine disorders like Cushing's syndrome in humans.

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.

Pre-trilostane and three-hour post-trilostane cortisol to monitor trilostane therapy in dogs

It is recommended that trilostane therapy of canine hyperadrenocorticism is monitored using an ACTH stimulation test, however this has never been validated. Three cortisol concentrations (pre-trilostane, 3-hour posttrilostane and 1-hour post-ACTH stimulation) were compared to a clinical score obtained from an owner questionnaire. There were 110 sets of 3 cortisol measurements and questionnaires obtained from 67 trilostane treated dogs. Questionnaire results were used to classify each dog as well or unwell. Well dogs were then categorised as having excellent, moderate or poor hyperadrenocorticism control, using thresholds produced by 14 independent veterinarians. Correlation co-efficients were used to compare the three cortisol concentrations to the owner score and the Kruskal Wallis and Mann-Whitney U tests were used to compare the three cortisol concentrations between categories of control. Cortisol cut-off values between significantly different categories were determined using ROC curves. Pre-trilostane and 3-hour post-trilostane cortisol were better correlated to the owner score and had cut-offs to differentiate between categories of control that had superior sensitivity and specificity results, than the post-ACTH cortisol. Iatrogenic hypoadrenocorticism was not detected in any unwell dog. This study shows that the pre-trilostane and 3-hour post-trilostane cortisol are potentially better monitoring methods than the ACTH stimulation test.

Evaluation of baseline cortisol concentration to monitor efficacy of twice-daily administration of trilostane to dogs with pituitary-dependent hyperadrenocorticism: 22 cases (2008-2012)

OBJECTIVE

To evaluate use of cortisol concentration prior to ACTH stimulation (baseline) to monitor efficacy of twice-daily administration of trilostane to dogs with pituitary-dependent hyperadrenocorticism (PDH).

DESIGN

Retrospective case series.

ANIMALS

22 dogs with PDH.

PROCEDURES

The database of a veterinary hospital was searched to identify dogs with PDH that were treated with the FDA-approved veterinary formulation of trilostane twice daily between January 1, 2008, and December 31, 2012. For each dog, signalment and details regarding each hospital visit including comorbidities, electrolyte concentrations, and clinical signs were extracted from the record. For each ACTH stimulation test performed, the respective correlations between baseline cortisol concentration and the cortisol concentration after ACTH stimulation (ACTH-stimulated cortisol concentration) and resultant decision regarding trilostane dose adjustment were determined. Excessive suppression of cortisol production was defined as an ACTH-stimulated cortisol concentration < 2.0 μg/dL. The ability of various baseline cortisol concentrations to predict whether a dog had excessive suppression of cortisol production was determined.

RESULTS

109 ACTH stimulation tests were performed for the 22 dogs. A baseline cortisol concentration > 3.2 μg/dL predicted that ACTH-stimulated cortisol concentration would be ≥ 2.0 μg/dL with 100% certainty; however, 14 of 64 tests with a baseline cortisol concentration > 3.2 μg/dL had an ACTH-stimulated cortisol concentration ≤ 3.2 μg/dL, which was suggestive of inadequate adrenocortical cortisol reserves.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that baseline cortisol concentration should not be used as the sole monitoring tool for management of dogs with PDH treated with trilostane twice daily.

Cortisol Response in Healthy and Diseased Dogs after Stimulation with a Depot Formulation of Synthetic ACTH

Background

The ACTH stimulation test is used to evaluate the adrenocortical reserve. Recently, the availability of the synthetic ACTH formulation was limited, causing major problems in clinical practice.

Objectives

The objective of this study was to evaluate poststimulation peak cortisol concentrations and the duration of the stimulatory effect of a depot ACTH preparation in dogs.

Animals

Twenty‐two healthy dogs, 10 dogs with suspected hypoadrenocorticism (HA) and 15 dogs with suspected hyperadrenocorticism (HC).

Methods

Prospective study. An ACTH stimulation test using a synthetic depot tetracosactide, administered intramuscularly (5 μg/kg or at least 0.1 mL) was performed. Blood samples for determination of cortisol were taken immediately before and 1, 2, 3, 4, 6, and 24 hours after stimulation.

Results

Peak cortisol concentrations were reached after 2–4 hours in all dogs. Cortisol concentrations 1 hour after stimulation were >9 μg/dL in all healthy dogs and >5 μg/dL in all dogs in which HA was excluded. None of the dogs with HA showed a cortisol‐increase above the detection‐limit of the assay. After 6 hours, cortisol concentrations had decreased in the healthy and HC group and were back to baseline after 24 hours.

Conclusions and Clinical Importance

The depot formulation can be used in place of the short‐acting ACTH to evaluate the adrenocortical reserve. Blood for peak cortisol concentrations should be drawn 3 hours after stimulation in cases in which HC is suspected; in HA‐suspected cases, blood sampling can take place after 1 hour. As the stimulatory effect is gone after 24 hours, interference with other hormonal tests is unlikely after that time.

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.

Urinary corticoid concentrations measured by 5 different immunoassays and gas chromatography-mass spectrometry in healthy dogs and dogs with hypercortisolism at home and in the hospital

Background

Determination of the urinary corticoid‐to‐creatinine ratio (UCCR) is an important screening test in the diagnosis of hypercortisolism (HC). However, urinary cortisol metabolites interfere with cortisol measurement in immunoassays, leading to decreased specificity. Gas chromatography‐mass spectrometry (GC‐MS) is considered the gold standard for steroid hormone analysis, because it provides a high level of selectivity and accuracy.

Objectives

To prospectively compare the UCCR of healthy dogs and dogs with HC determined by 5 different immunoassays and by GC‐MS and to evaluate the influence of veterinary care on UCCR.

Animals

Twenty healthy dogs; 18 dogs with HC.

Methods

Urine was collected in the hospital and again after 6 days at home. Three chemiluminescence immunoassays (Access 2, Beckmann; Immulite 2000, DPC Siemens, with and without trichloromethane extraction) and 2 RIAs (Utrecht in house; Access Beckmann) were used. GC‐MS analyses were performed with Agilent 6890N/5973N. Urinary corticoid concentrations were related to urinary creatinine concentrations.

Results

Immunoassay results were significantly higher compared to GC‐MS results. Evaluation of bias plots and clinical assessment made on the basis of the assay results of each dog indicated substantial disagreement among the assays. Sensitivity varied from 37.5 to 75% and with selected assays was lower in samples from day 6 compared to day 0. GC‐MS was not superior to the immunoassays in discriminating healthy from HC dogs.

Conclusions and Clinical Importance

Considerable variation must be anticipated comparing different urinary cortisol assays. Establishing an assay‐ and laboratory‐specific reference range is critical when using UCCR.

Comparison of adrenocorticotropic hormone stimulation test results started 2 versus 4 hours after trilostane administration in dogs with naturally occurring hyperadrenocorticism

Background

Trilostane medical treatment of naturally occurring hyperadrenocorticism (NOH) in dogs is common, as is use of the adrenocorticotropic hormone (ACTH) stimulation test (ACTHst) in monitoring response to treatment. There is uncertainty regarding when the ACTHst should be started relative to time of trilostane administration.

Objective

To compare ACTHst results in dogs being treated for NOH with trilostane when the test is begun 2 versus 4 hours after trilostane administration.

Animals

Twenty‐one privately owned dogs with NOH, each treated with trilostane for at least 30 days.

Methods

Each dog had 2 ACTHst completed, 1 started 2 hours and the other 4 hours after trilostane administration. The second test was started no sooner than 46 hours and no later than 74 hours after the first.

Results

For all 21 dogs, the mean post‐ACTH serum cortisol concentration from tests started 2 hours after trilostane administration (5.4 ± 3.7 μg/dL) was significantly lower (P = .03) as compared with results from the tests started 4 hours after administration (6.5 ± 4.5 μg/dL).

Conclusions

Results of ACTHst started at different times yield significantly different results. Dogs with NOH, treated with trilostane, and monitored with ACTHst results should have all of their subsequent ACTHst tests begun at or about the same time after trilostane administration.