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

Abstract

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.

Keywords: Hyperadrenocorticism; Trilostane.

Figure 1

Individual postadrenocorticotropic hormone stimulation serum cortisol concentrations from 15 dogs with naturally occurring hyperadrenocorticism whose results on tests started 2 hours after the administration of trilostane were lower than on tests begun 4 hours after. The 3 data sets with symbols are the results from 3 dogs with adrenocortical tumor‐associated hyperadrenocorticism, all other data sets are from dogs with pituitary‐dependent hyperadrenocorticism.

Figure 2

Individual postadrenocorticotropic hormone stimulation serum cortisol concentrations from 5 dogs with naturally occurring hyperadrenocorticism whose results on tests started 4 hours after the administration of trilostane were lower than results on tests begun 2 hours after. The data set with symbols is the results from the dog with adrenocortical tumor‐associated hyperadrenocorticism, all other data sets are from dogs with pituitary‐dependent hyperadrenocorticism.