How do I monitor a dog on trilostane for hyperadrenocorticism and what are the dose adjustment criteria?

Question

Accepted Answer

Trilostane monitoring combines consistent ACTH stimulation test (ACTH-st) timing with clinical sign assessment, and dose adjustment decisions should weight both equally. No single laboratory variable reliably discriminates well-controlled from under-controlled dogs, making owner-reported clinical signs the primary indicator of control.71011 The ACTH-st should be performed 3–5 hours after trilostane administration according to the 2023 AAHA guidelines, or 4–6 hours after administration per the Vetoryl package insert. The critical constraint is consistency: because post-ACTH cortisol concentrations differ significantly depending on when the test is started — with values at 2 hours post-administration being measurably lower than at 4 hours — the same post-administration interval must be used at every recheck.125 For dogs on twice-daily dosing, the ACTH-st should always follow the higher of the two doses.5 The monitoring schedule is: recheck with ACTH-st and serum biochemistry (electrolytes, renal and hepatic function) at 10–14 days after initiation, then at 30 days, then at 90 days, then every 3 months thereafter. An additional ACTH-st and biochemistry panel is required 10–14 days after every dose adjustment.25 Good control is defined by the Vetoryl label as a post-ACTH cortisol of 1.45–9.1 μg/dL (40–250 nmol/L), in conjunction with favorable clinical signs.2 The 2023 AAHA guidelines frame the primary purpose of the 2-week recheck as ruling out excessive suppression rather than confirming adequate control, and dose increases are not typically made at that first visit.5 Dose adjustment criteria are as follows. If post-ACTH cortisol is below 1.45 μg/dL (< 40 nmol/L), with or without electrolyte abnormalities (hyperkalemia, hyponatremia), trilostane should be temporarily discontinued until clinical signs of hyperadrenocorticism recur and post-ACTH cortisol returns to 1.45–9.1 μg/dL (40–250 nmol/L), at which point trilostane may be reintroduced at a lower dose.2 The Merck