Use of urine cortisol:creatinine ratio versus adrenocorticotropic hormone stimulation testing for monitoring mitotane treatment of pituitary-dependent hyperadrenocorticism in dogs

Abstract

Objective To evaluate use of urine cortisol-to-creatinine ratio (UC:C) as a means of monitoring response to long-term mitotane treatment in dogs with pituitary-dependent hyperadrenocorticism. Design Prospective uncontrolled study. Animals 101 dogs with pituitary-dependent hyperadrenocorticism. Procedure Urine samples were obtained from dogs on the morning an ACTH stimulation test was performed, and owners were asked their opinion on the health of their dog to monitor response to mitotane treatment. Urine was assayed for cortisol and creatinine concentrations, and UC:C was calculated. The UC:C was compared with post-ACTH plasma cortisol concentration. Results Post-ACTH plasma cortisol concentration was used to categorize each dog's response to mitotane treatment. The UC:C did not correlate satisfactorily with results of ACTH stimulation testing. Twenty-seven of 85 (32%) dogs would have been incorrectly considered as having received appropriate doses using UC:C. In addition, 16 dogs that received overdoses could not be distinguished from 29 dogs that received appropriate doses. Clinical Implications UC:C does not provide a consistent, correct assessment of mitotane-induced adrenocortical destruction. The ACTH stimulation test, although more time-consuming and expensive, is recommended for monitoring response to mitotane treatment. (J Am Vet Med Assoc 1997;211:1002–1004)