Trilostane Monitoring: Pre-Dose Cortisol vs ACTH Stimulation Test in Dogs

TL;DR

Pre-trilostane and three-hour post-trilostane cortisol concentrations may discriminate excellent from suboptimal clinical control better than the post-ACTH stimulation test in dogs treated with trilostane for hyperadrenocorticism, supporting pre-dose cortisol as a practical first-line monitoring tool.

What just dropped

• A cohort study in 110 trilostane-treated dogs found that pre-trilostane cortisol and three-hour post-trilostane cortisol both correlated significantly with owner-assessed clinical control scores, and both outperformed post-ACTH stimulation cortisol at discriminating excellent from suboptimal control. A pre-trilostane cortisol cut-off of 138 nmol/L showed 86.5% specificity for excellent control in this cohort. (https://pmc.ncbi.nlm.nih.gov/articles/PMC5256409/)

Context

Trilostane (Vetoryl) is authorised for treatment of pituitary-dependent and adrenal-dependent hyperadrenocorticism in dogs. The pivotal early clinical data showed complete resolution of polyuria and polydipsia in 70% of treated dogs and skin changes in 62%, with post-ACTH cortisol falling below 250 nmol/L in 81% within the first month of treatment. Median survival time in the original cohort was 549 days, with only two of 78 dogs developing clinical hypoadrenocorticism. (https://pubmed.ncbi.nlm.nih.gov/12120922/)

Conventional monitoring relies on post-ACTH stimulation cortisol, but there has been long-standing lack of consensus on target concentrations, with published target values ranging from 15 to 250 nmol/L across different studies. A pre-stimulation or trough cortisol has been evaluated as a simpler alternative.

In the 110-dog cohort study, the pre-trilostane cortisol (collected at least 12 hours after the last dose) was slightly superior to the three-hour post-trilostane cortisol and had the added advantage of being more useful for signalling potential oversuppression. Dogs with pre-trilostane cortisol below 40 nmol/L were flagged as potentially at risk of iatrogenic hypocortisolism. The authors proposed a potential target range for pre-trilostane cortisol of greater than 40 and less than 138 nmol/L, while acknowledging that further studies are needed to refine these cut-offs and that results may not be directly extrapolable across different cortisol assay platforms.

What this changes in Trilostane for Canine Hyperadrenocorticism (https://www.thevoyage.ai/forvets/knowledge/trilostane-canine-hyperadrenocorticism)

The emerging data on pre-trilostane cortisol offers a logistically simpler monitoring option for practices managing large HAC caseloads. A single trough cortisol sample, collected at the appropriate interval after the last dose, avoids the time and cost of ACTH stimulation testing in dogs that are clinically well and have stable owner assessment scores. For dogs where the pre-trilostane cortisol falls outside the candidate range or where clinical signs are ambiguous, an ACTH stimulation test remains appropriate. These monitoring choices should always be made in conjunction with clinical assessment, the product datasheet, and individual patient history, per current best practice.

Voyage Clinical Desk: https://www.thevoyage.ai/forvets/ask?context=trilostane-canine-hyperadrenocorticism

References

1. Norman EJ et al. 2017. Pre-trilostane and three-hour post-trilostane cortisol to monitor trilostane therapy in dogs. Vet Rec 180(7). https://pmc.ncbi.nlm.nih.gov/articles/PMC5256409/
2. Neiger R et al. 2002. Trilostane therapy for treatment of pituitary-dependent hyperadrenocorticism in 78 dogs. J Vet Intern Med 16(3):291-301. https://pubmed.ncbi.nlm.nih.gov/12120922/

---

Related reads

• Trilostane (Vetoryl) for Canine Hyperadrenocorticism: Evidence and Monitoring