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

The aim of this work was to evaluate the response of dogs with pituitary-de pendent hyperadrenocorticism to treatment with mitotane. The relationship b etween duration of initial phase of therapy and the initial value of urine cortisol/creatinine ratio (UCCR) was studied. All 14 dogs with pituitary-de pendent hyperadrenocorticism were treated. Therapeutic protocol of selectiv e adrenocorticolysis was used. The induction dose of mitotane was 25 mg/kg daily. The length of initial phase of therapy was determined individually a n the basis of cortisol production changes, which were monitored by immunor eactive cortisol in urine (UCCR) every 2-5 days during the initial phase of treatment. High-dose dexamethasone suppression test was used to differenti ate between the pituitary-dependent and adrenal-dependent form of the disea se, and the UCCR was measured after dexamethasone suppression. The value of the initial UCCR fluctuated between 58-586 x 10(-6), the median of UCCR wa s 138 x 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 induc tion dose Of mitotane ran-ed from 250 to 1600 mg/kg b.w. No linear dependen ce between the length of initial phase of therapy and the pre-treatment val ues of UCCR was found by regression an correlation analysis.