Results of non-selective adrenocorticolysis by o,p '-DDD in 129 dogs with pituitary-dependent hyperadrenocorticism

One hundred and twenty-nine dogs with pituitary-dependent hyperadrenocortic ism were treated according to a protocol aimed at the complete destruction of the adrenal cortices by the administration of o,p'-DDD (mitotane) at a d aily dose of 50 to 75 mg/kg bodyweight for 25 days. On the third day, gluco corticoid and mineralocorticoid supplementation was begun for the induced a drenocortical insufficiency. The first followup examination after completio n of the 25-day course and the subsequent twice-yearly follow-up examinatio ns included physical examination and measurements of plasma concentrations of sodium and potassium to optimise substitution therapy. In 19 dogs the fu ll course of 25 days treatment could not be completed. Of the 110 dogs whic h received the full course of treatment, the administration had to be stopp ed temporarily in 32 because of side-effects, such as anorexia and vomiting . The actual dose of o,p'-non administered was not significantly different in the dogs with and without these side-effects. Clinical remission occurre d in 111 dogs (86 per cent), of which 43 (39 per cent) had a relapse. The e stimated one-year disease-free fraction was 77 per cent (95 per cent confid ence interval [CI]: 67 to 85 per cent). The estimated one-year survival fra ction was 80 per cent (95 per cent CI: 71 to 87 per cent), the two-year sur vival was 69 per cent (95 per cent a: 59 to 78 per cent), and the three-yea r survival was 61 per cent (95 per cent a: 49 to 71 per cent). The bodyweig ht and age of the dog, and vomiting occurring during the period of treatmen t, were positively correlated with the length of the disease-free period, w hereas weakness during the treatment and resistance to dexamethasone suppre ssion of the urinary corticoid/creatinine ratios at the start of the treatm ent were associated with a relatively short survival time.