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.The Veterinary…+2

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.Journal of Vete…+2 For dogs on twice-daily dosing, the ACTH-st should always follow the higher of the two doses.AAHA Clinical G…

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.FDA DailyMed An…+1

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.FDA DailyMed An… 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.AAHA Clinical G…

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.FDA DailyMed An… The Merck Veterinary Manual specifies that a post-ACTH cortisol below 20 nmol/L warrants stopping trilostane for 48–72 hours and repeating the ACTH-st before reintroduction.MSD Vet Manuals If post-ACTH cortisol exceeds 200 nmol/L, the dose should be increased.MSD Vet Manuals After the first month of treatment, dose increases are typically 25–50% based on available capsule sizes.AAHA Clinical G…

Once-daily dosing is the starting point, but twice-daily dosing is appropriate when clinical signs are not controlled for the full day. To convert, divide the total daily dose into two portions given 12 hours apart — portions need not be equal, with the larger dose given in the morning. For example, a dog on 90 mg/day would receive 60 mg in the morning and 30 mg in the evening.FDA DailyMed An… Most authors currently recommend an initial dose of approximately 1 mg/kg PO q12h for twice-daily protocols, with final doses often plateauing at 0.5–2.0 mg/kg.Journal of Vete…

Baseline (pre-pill) cortisol and 3-hour post-trilostane cortisol show better correlation with owner-assessed clinical control than post-ACTH cortisol, and pre-trilostane cortisol has been advocated as a reliable supplementary monitoring variable.Veterinary Reco…+1 However, a pre-pill cortisol above 3.2 μg/dL predicts that post-ACTH cortisol will be ≥ 2.0 μg/dL with 100% certainty, but does not exclude inadequate adrenocortical reserve — 14 of 64 tests with pre-pill cortisol above 3.2 μg/dL still had post-ACTH cortisol ≤ 3.2 μg/dL, indicating that baseline cortisol alone is insufficient as the sole monitoring tool.Journal of the…

Serum haptoglobin is the strongest objective laboratory predictor of clinical control among 12 variables evaluated. A haptoglobin cutoff of 151 mg/dL correctly identified 90.0% of well-controlled dogs (specificity) and 65.6% of under-controlled dogs (sensitivity). Alanine aminotransferase (ALT) ≥ 86 U/L and gamma-glutamyl transferase (γGT) ≥ 5.8 U/L are also significantly associated with poor trilostane control.Journal of Vete…

Iatrogenic hypoadrenocorticism is a rare but life-threatening complication. It can develop as early as 4 days after starting trilostane and has been reported at doses ranging from 1 to 8 mg/kg/day. Concurrent illness appears to precipitate clinical signs in previously subclinical dogs, and permanent adrenal insufficiency requiring lifelong replacement therapy is possible.Journal of Smal…

Would you like guidance on managing a dog that develops clinical signs of hypoadrenocorticism while on trilostane?