Association between post-ACTH cortisol and trilostane dosage in dogs with pituitary-dependent hypercortisolism

•Balancing the initial dosage of trilostane is crucial to avoid iatrogenic hypocortisolism without compromising disease control of canine pituitary-dependent hypercortisolism (PDH).•It was hypothesized that post-ACTH cortisol at the time of PDH diagnosis could serve as predictor for the requirement of additional doses of trilostane to manage the disease.•Post-ACTH cortisol ≥ 27 μg/dL at diagnosis are 96% more likely to require as increase in trilostane dosage to achieve satisfactory control of PDH. Trilostane is the current treatment of choice for managing pituitary-dependent hypercortisolism (PDH) in dogs. While prescribing higher initial doses may elevate the risk of iatrogenic hypocortisolism, opting for more conservative approach could result in delayed disease control, since most individuals end up requiring dosage increases. The adrenocorticotrophin stimulation test (ACTHst), a widely recognized hormonal test for assessing adrenal function, is an essential tool for monitoring the pharmacological treatment of canine hypercortisolism (CH) that can also be used for diagnostic purposes. The aim of this study was to investigate the relationship between post-ACTH cortisol (cpACTH) at PDH diagnosis and the required trilostane dose for sign control and endogenous cortisol regulation in dogs, considering a hypothesis that higher serum cpACTH concentration would necessitate a higher trilostane dosage for disease management. Data for 43 dogs with PDH had their diagnostic cpACTH recorded and correlated to the trilostane dosage necessary to control clinical signs and achieve satisfactory cortisol levels (ideally 2-7 μg/dL). The odds ratio (p=0.042) suggests that dogs with cpACTH ≥ 27 μg/dL at diagnosis are 96% more likely to need a higher trilostane dosage for achieving satisfactory control of PDH. Thus, cpACTH was found to be associated with the final trilostane dose for controlling PDH in dogs.