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Abstract

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).

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, 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 ≥ 28 nmol/L but ≤ 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 × 10−6 were always classified as having excess cortisol secretion.

Conclusion and Clinical Relevance

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 × 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 ≤ 79 × 10−6 would be inconclusive. (Am J Vet Res 1998;59:258–261)

Free access
in American Journal of Veterinary Research