USE OF THE URINE CORTISOL-TO-CREATININE RATIO FOR MONITORING DOGS WITH PITUITARY-DEPENDENT HYPERADRENOCORTICISM DURING INDUCTION TREATMENT WITH MITOTANE (O,P'-DDD)

Objective-To determine whether the urine cortisol-to-creatinine ratio (UCCR) could replace the ACTH stimulation test in monitoring effective ness of mitotane induction treatment in dogs with pituitary-dependent hyperadrenocorticism (PDH). Animals-15 dogs with PDH. Procedure-All 15 dogs were given an induction dose of mitotane (o,p'-DDD: 35 to 50 mg/ kg of body weight/d) for 3 to 14 days. During the induction period, fr ee-catch morning urine samples were collected for determination of UCC R, followed by ACTH stimulation testing, every other day. Treatment re sponse was divided into 3 categories: weil-controlled PDH (post-ACTH s erum cortisol concentration greater than or equal to 28 nmol/L but les s than or equal to 138 nmol\L), deficient cortisol secretion (post-ACT H serum cortisol concentration < 28 nmol/L), and excess cortisol secre tion (post-ACTH serum cortisol concentration > 138 nmol/L). Results-Th e linear relation between UCCR and post-ACTH serum cortisol concentrat ion was significant (P < 0.001); however, the prediction intervals sur rounding the line were too broad to be clinically useful. The UCCR ove rlapped among the 3 categories of treatment response. Nevertheless, do gs with PDH receiving mitotane induction treatment and with UCCR > 79 x 10(-6) were always classified as having excess cortisol secretion. C onclusion and Clinical Relevance-The UCCR failed to predict post-ACTH cortisol concentration during mitotane induction treatment sufficientl y close to be a clinically reliable indicator of treatment control. Se emingly, however, UCCR > 79 x 10(-6) obtained from a dog with PDH duri ng mitotane induction would indicate inadequate adrenal cortex destruc tion and the need for continued mitotane induction; UCCR less than or equal to 79 x 10(-6) would be inconclusive.