Although the effects of trilostane are well known, no studies have examined these effects over 24 hours after its administration. This study measured hormone and serum electrolyte concentrations in 9 dogs with pituitary-dependent hyperadrenocorticism (PDH) treated with trilostane.
Thirty days after therapy initiation, samples were taken from central venous catheters at -30, 0 (baseline), 15, 30, 60, and 90 minutes, and 2, 3, 4, 6, 8, 12, 16, 20, and 24 hours after trilostane administration. Mean trilostane dose was 4.2 ± 0.55 mg/kg q24h. There were significant changes in all parameters except sodium and ionized calcium, although the increase in aldosterone and surprising decrease in potassium concentrations were not clinically relevant. Renin activity increased at 6–20 hours and may be responsible for the increase in aldosterone. Cortisol was decreased significantly from 2–4 hours after trilostane administration. Thus, ACTH stimulation testing for therapeutic monitoring should potentially be carried out in this timeframe rather than the traditional 4–6 hour recommendation.
Endogenous ACTH increased significantly after 3 hours, decreasing to baseline after 12 hours; however, there was marked individual variation in ACTH with only minimal changes over 24 hours in some dogs. The use of endogenous ACTH measurement for evaluation of therapeutic success of trilostane is questionable.