To evaluate the efficacy of trilostane in treating dogs with pituitary-dependent hyperadrenocorticism.


Prospective clinical trial using client-owned dogs with pituitary-dependent hyperadrenocorticism treated at University Veterinary Centre, Sydney from September 1999 to July 2001.


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.


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.


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.