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 effectiveness of mitotane induction treatment in dogs with pituitary-dependent hyperadrenocorticism (PDH).


METHODS
15 dogs with PDH.


METHODS
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, free-catch morning urine samples were collected for determination of UCCR, followed by ACTH stimulation testing, every other day. Treatment response was divided into 3 categories: well-controlled PDH (post-ACTH serum cortisol concentration > or = 28 nmol/L but < or = 138 nmol/L), deficient cortisol secretion (post-ACTH serum cortisol concentration < 28 nmol/L), and excess cortisol secretion (post-ACTH serum cortisol concentration > 138 nmol/L).


RESULTS
The linear relation between UCCR and post-ACTH serum cortisol concentration was significant (P < 0.001); however, the prediction intervals surrounding the line were too broad to be clinically useful. The UCCR overlapped among the 3 categories of treatment response. Nevertheless, dogs with PDH receiving mitotane induction treatment and with UCCR > 79 x 10(-6) were always classified as having excess cortisol secretion.


CONCLUSIONS
The UCCR failed to predict post-ACTH cortisol concentration during mitotane induction treatment sufficiently close to be a clinically reliable indicator of treatment control. Seemingly, however, UCCR > 79 x 10(-6) obtained from a dog with PDH during mitotane induction would indicate inadequate adrenal cortex destruction and the need for continued mitotane induction; UCCR < or = 79 x 10(-6) would be inconclusive.
Randolph
J F
JF
Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA.
Toomey
J
J
Center
S A
SA
Scarlett
J M
JM
Reimers
T
T
Graham
P
P
Nachreiner
R F
RF
D000308:Adrenocortical Hyperfunction / Q000188:drug therapy / Q000209:etiology / Q000652:urine / Q000662:veterinary*; D000324:Adrenocorticotropic Hormone; D000818:Animals; D018931:Antineoplastic Agents, Hormonal / Q000627:therapeutic use*; D015415:Biomarkers / Q000097:blood / Q000652:urine; D003404:Creatinine / Q000652:urine*; D004283:Dog Diseases; D004285:Dogs; D016903:Drug Monitoring / Q000379:methods / Q000662:veterinary; D005260:Female; D006854:Hydrocortisone / Q000097:blood / Q000652:urine*; D008297:Male; D008939:Mitotane / Q000627:therapeutic use*; D010900:Pituitary Diseases / Q000188:drug therapy / Q000652:urine / Q000662:veterinary*; D010912:Pituitary-Adrenal Function Tests / Q000662:veterinary; D013997:Time Factors
D018931:Antineoplastic Agents, Hormonal; D015415:Biomarkers; D008939:Mitotane; D000324:Adrenocorticotropic Hormone; D003404:Creatinine; D006854:Hydrocortisone