Objective: To evaluate effectiveness and incidence of adverse reactions to twice-daily lower-dose oral administration of trilostane in the treatment of dogs with naturally occurring hyperadrenocorticism (NOH).
Design: Clinical trial.
Animals: 47 dogs with NOH.
Procedures: 47 dogs were treated orally with trilostane (0.21 to 1.1 mg/kg [0.1 to 0.5 mg/lb], q 12 h). All dogs were reevaluated at 2 weeks and 2 months, 38 dogs at 6 months, and 28 dogs at 1 year of treatment.
Results: 9 of 47 dogs had an adrenocortical tumor causing NOH, and all had good responses after 2 months (mean trilostane dosage, 0.89 mg/kg [0.40 mg/lb], q 12 h). All successfully underwent surgical adrenal tumor extirpation. Thirty-eight dogs had pituitary-dependent hyperadrenocorticism (PDH); 15 dogs did not require a dose increase during the study, and at each of 4 reevaluations, 10 of 15, 13 of 15, 14 of 15, and 11 of 11 had a good response. Twenty-three dogs with PDH had their dose or frequency of trilostane administration increased during the study. Mean trilostane dosage at 1-year reevaluation in dogs with a good response was 1.7 mg/kg (0.8 mg/lb), twice daily, or 1.1 mg/kg, 3 times daily. At each of 4 reevaluations, 17 of 23, 14 of 23, 17 of 23, and 13 of 17 dogs with PDH had a good response. Five dogs became ill because of trilostane-induced adverse effects, but only 1 required hospitalization.
Conclusions and clinical relevance: Administration of initial lower doses of trilostane to dogs with NOH is effective.