Mitotane (o, DDD) resistance in a dog with pituitary-dependent hyperadrenocorticism and phaeochromocytoma

A dog was presented with a 2 year history of polyuria and polydipsia due to pituitary-dependent hyperadrenocorticism. A low-dose dexamethasone suppression test and measurement of plasma ACTH concentration confirmed the diagnosis. Treatment was instituted with mitotane at 44 mg/kg/day and then 88 mg/kg/d without complete resolution of signs. The dog collapsed with signs consistent with liver disease and was euthanased. Necropsy revealed a phaeochromocytoma of the left adrenal medulla with extensive metastases to the liver. A chromophobe adenoma of the pars intermedia of the pituitary was found.     

Medical management of pituitary-dependent hyperadrenocorticism: mitotane versus trilostane

Pituitary-dependent hyperadrenocorticism is a common endocrine disorder in dogs in the United States. Once a diagnosis is established, a decision must be made whether or not to pursue treatment, and if so, which medication to use. Historically, mitotane (Lysodren, o,p'-DDD, Bristol-Myers Squibb, New York) has been the most commonly used treatment for medical management. Its use is complicated and comes with many potential side effects, making many practitioners wary of its use. Recently, trilostane has been proven to be an effective treatment of pituitary-dependent hyperadrenocorticism and is approved for use in other countries. Treatment with trilostane is somewhat simpler and the incidence of side effects seems to be less when compared with mitotane therapy. Either treatment can be a safe and effective method of treatment for pituitary-dependent hyperadrenocorticism when the practitioner and client are well educated regarding their use and an appropriate monitoring protocol is used.