USE OF URINE CORTISOL-CREATININE RATIO VERSUS ADRENOCORTICOTROPIC HORMONE STIMULATION TESTING FOR MONITORING MITOTANE TREATMENT OF PITUITARY-DEPENDENT HYPERADRENOCORTICISM IN DOGS

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 hyperad renocorticism. 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 mitota ne treatment. Urine was assayed for cortisol and creatinine concentrat ions, and UC:C was calculated. The UC:C was compared with post-ACTH pl asma cortisol concentration. Results-Post-ACTH plasma cortisol concent ration was used to categorize each dog's response to mitotane treatmen t. The UC:C did not correlate satisfactorily with results of ACTH stim ulation testing. Twenty-seven of 85 (32%) dogs would have been incorre ctly considered as having received appropriate doses using UC:C. In ad dition, 16 dogs that received overdoses could not be distinguished fro m 29 dogs that received appropriate doses Clinical Implications-UC:C d oes not provide a consistent, correct assessment of mitotane-induced a drenocortical destruction. The ACTH stimulation test, although more ti me-consuming and expensive, is recommended for monitoring response to mitotane treatment.