Trilostane treatment in dogs with pituitary‐dependent hyperadreno‐corticism

OBJECTIVE: To evaluate the efficacy of trilostane in treating dogs with pituitary‐dependent hyperadrenocorticism. DESIGN: Prospective clinical trial using client‐owned dogs with pituitary‐dependent hyperadrenocorticism treated at University Veterinary Centre, Sydney from September 1999 to July 2001. PROCEDURE: Thirty dogs with pituitary‐dependent hyperadrenocorticism treated with trilostane, a competitive inhibitor β‐HSD, were monitored at days 10, 30 and 90 then 3‐monthly by clinical examination, tetracosactrin stimulation testing, urinary corticoid:creatinine ratio measurement and by client questionnaire. RESULTS: Twenty‐nine of 30 dogs were successfully treated with trilostane (median dose 16.7 mg/kg; range 5.3 to 50 mg/kg, administered once daily); one responded favourably but died of unrelated disease before full control was achieved. CONCLUSION: Trilostane administration controlled pituitary‐dependent hyperadrenocorticism in these dogs. It was safe, effective and free of side‐effects at the doses used. Most dogs were initially quite sensitive to the drug for 10 to 30 days, then required higher doses until a prolonged phase of stable dose requirements occurred. Urinary corticoid:creatinine ratio was useful in assessing duration of drug effect. Some dogs treated for more than 2 years required reduction or temporary cessation of drug because of iatrogenic hypoadrenocorticism.