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

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.

Clinical and microbiological characterization of subclinical bacteriuria and sporadic bacterial cystitis in dogs with spontaneous hypercortisolism

Study's aims were to characterize subclinical bacteriuria (SB) and sporadic bacterial cystitis (SBC) in dogs with spontaneous hypercortisolism (HC). Prospective cross-sectional design divided patients as newly diagnosed (n = 27), poorly controlled (n  = 21), well controlled (n  = 34), and controls (n  = 19). Urine culture positive results were identified by MALDI-TOF and submitted to antibiogram. Escherichia coli was the most common microorganism (36%). The majority of positive cultures in HC were SB (12.2%). All 4.1% SBC cases were in well controlled HC cases. Bacteriuria correlated with low urine specific gravity and low lymphocyte count. HC degree of control correlated with leukocyturia. SB/SBC cases were treated based in antimicrobial susceptibility leading to microbiological cure in 75% of HC cases. Persistent infections occurred only in SB cases, all by E. coli which became more resistant. SB/SBC prevalence in canine HC is actually lower. Further evidence for current ISCAID guideline contraindication for SB treatment due to HC were provided.

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.

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.

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.

Update on the use of trilostane in dogs

Many articles published in the past few years have contributed to a better understanding of the use of trilostane in dogs. Trilostane is a competitive inhibitor of 3β-hydroxysteroid dehydrogenase, the enzyme essential for synthesis of cortisol and all other steroids. Trilostane is reported to be safe and effective in the treatment of pituitary-dependent hyperadrenocorticism (HAC), adrenal-dependent HAC, and alopecia X. While trilostane controls most of the clinical signs associated with HAC, abnormalities such as hypertension, hypercoagulability, and proteinuria may persist despite therapy. Because the duration of cortisol suppression after a dose of trilostane is often less than 12 hours, many dogs with HAC could benefit from low dose trilostane treatment every 12 hours. Many controversies regarding trilostane still exist. This review provides a comprehensive commentary on trilostane's indications, mode of action, dose, monitoring, efficacy, and adverse effects.

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.

Uso de baixa dose de ACTH sintético no teste de estimulação da função adrenal para o diagnóstico e controle do hiperadrenocorticismo canino: avaliação da eficácia diagnóstica

RESUMO: O teste de estimulação com ACTH é o teste de escolha para realizar o controle dos valores de cortisol endógeno em pacientes sob tratamento para o hiperadrenocorticismo canino, podendo ser utilizado também para diagnosticar a doença. Os protocolos atuais utilizam doses que variam entre 5ug/kg a 250ug/animal por administração intravenosa ou intramuscular. Não se constatam estudos com doses menores que as de 5ug/kg em pacientes portadores de hiperadrenocorticismo. No presente estudo, foi testada a dose de 1ug/kg/IV; comparada à dose consagrada de 5ug/kg/IV, em grupos de animais suspeitos de HAC (HAC Diag), animais portadores de HAC e em tratamento (HAC Control) e animais sadios (Sadios). Na dose de 1ug/kg/IV, os valores basais de cortisol dos Sadios foram iguais à média 2,40ug/dL(+/-1,57ug/dL), dos HAC control foi de média 1,53ug/dL(+/-0,93,ug/dL) e dos HAC diag foi média 3,37ug/dL(+/-1,57ug/dL). Os valores pós-ACTH na dose de 1ug/kg foram de média 11,43ug/dL(+/-2,46ug/dL) para animais sadios, 2,67ug/dL(+/-1,39ug/dL) para o grupo HAC Control e média 16,56ug/dL(+/-7,62ug/dL) para o grupo HAC Diag. Os valores basais de cortisol na dose de 5ug/kg foram 0,89ug/dL(+/-0,23ug/dL) para o grupo HAC Control; média 3,08ug/dL(+/-1,99 ug/dL) para o grupo HAC Diag. Os valores pós-ACTH na dose de 5ug/kg foram de média 3,71ug/dL(+/-1,57ug/dL), para o grupo HAC control e média 22,52ug/dL (+/-8,75ug/dL) para o grupo HAC diag. Analisando-se os resultados obtidos, constatou-se que as doses 1 e 5ug/kg de ACTH sintético não diferem entre si, promovendo o mesmo tipo de variação nos valores de cortisol (ANOVA; p=0,225). Também, que a dose de 1ug/kg de ACTH foi igualmente eficaz na elevação dos níveis de cortisol nos três grupo testados (Sadios, HAC Control e HAC Diag; ANOVA, p<0,05). E, pelo teste de Dunn observamos que o grupo HAC control apresenta Δ-cortisol (delta =diferença entre cortisol após estimulo e o cortisol basal) significativamente menor que o dos grupos diagnóstico (p<0,05) e animais sadios (p<0,05). Concluiu-se que a dose de 1ug/kg de ACTH sintético pode ser utilizada com eficácia para a realização do teste de estimulação com ACTH.

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.

Comparison of 2 Doses for ACTH Stimulation Testing in Dogs Suspected of or Treated for Hyperadrenocorticism

BACKGROUND

Lowering the cosyntropin dose needed for ACTH stimulation would make the test more economical.

OBJECTIVES

To compare the cortisol response to 1 and 5 μg/kg cosyntropin IV in dogs being screened for hyperadrenocorticism (HAC) and in dogs receiving trilostane or mitotane for pituitary-dependent HAC.

ANIMALS

Healthy dogs (n = 10); client-owned dogs suspected of having HAC (n = 39) or being treated for pituitary-dependent HAC with mitotane (n = 12) or trilostane (n = 15).

PROCEDURES

In this prospective study, healthy dogs had consecutive ACTH stimulation tests to ensure 2 tests could be performed in sequence. For the first test, cosyntropin (1 μg/kg IV) was administered; the second test was initiated 4 hours after the start of the first (5 μg/kg cosyntropin IV). Dogs suspected of having HAC or being treated with mitotane were tested as the healthy dogs. Dogs receiving trilostane treatment were tested on consecutive days at the same time post pill using the low dose on day 1.

RESULTS

In dogs being treated with mitotane or trilostane, the 2 doses were pharmacodynamically equivalent (90% confidence interval, 85.1-108.2%; P = 0.014). However, in dogs suspected of having HAC, the doses were not pharmacodynamically equivalent (90% confidence interval, 73.2-92.8%; P = 0.37); furthermore, in 23% of the dogs, clinical interpretation of test results was different between the doses.

CONCLUSIONS AND CLINICAL RELEVANCE

For dogs suspected of having HAC, 5 μg/kg cosyntropin IV is still recommended for ACTH stimulation testing. For dogs receiving mitotane or trilostane treatment, a dose of 1 μg/kg cosyntropin IV can be used.

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 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.