Evaluation of pituitary-dependent hyperadrenocorticism response to mitotane treatment in dogs. Length of initial phase of treatment in relation to initial value of urine cortisol/creatinine ratio

Abstract

The aim of this work was to evaluate the response of dogs with pituitary-dependent hyperadrenocorticism to treatment with mitotane. The relationship between duration of initial phase of therapy and the initial value of urine cortisol/creatinine ratio (UCCR) was studied. All 14 dogs with pituitary-dependent hyperadrenocorticism were treated. Therapeutic protocol of selective adrenocorticolysis was used. The induction dose of mitotane was 25 mg/kg daily. The length of initial phase of therapy was determined individually on the basis of cortisol production changes, which were monitored by immunoreactive cortisol in urine (UCCR) every 2-5 days during the initial phase of treatment. High-dose dexamethasone suppression test was used to differentiate between the pituitary-dependent and adrenal-dependent form of the disease, and the UCCR was measured after dexamethasone suppression. The value of the initial UCCR fluctuated between 58-586 × 10-6, the median of UCCR was 138 × 10-6. Initial phase of therapy lasted 10-64 days. Mean length of initial therapy was 17 days with a median of 14.5 day. The cumulative induction dose of mitotane ranged from 250 to 1600 mg/kg b.w. No linear dependence between the length of initial phase of therapy and the pre-treatment values of UCCR was found by regression and correlation analysis.