400 DISEASES/DISORDERS
THERAPEUTICS
Surgical Considerations
Hypophysectomy: described, but generally not recommended for treatment of PDH
because of the difficulty of the procedure and the need for intensive monitoring and
life-long hormonal supplementation.Adrenalectomy is a demanding procedure not generally used for the treatment of PDH
in dogs.
Surgery is probably the treatment of choice for adrenocortical adenomas and small
carcinomas unless the patient is a poor surgical risk.
Radiation Therapy for Pituitary Tumors
Radiation therapy successful for pituitary tumors; availability limited.
Drugs of Choice
Mitotane (o, p’-DDD):
Cytotoxic drug causing progressive necrosis of the zona fasciculata and zona
reticularis of the adrenal gland
Medical management of both PDH and ADH in dogs
Mitotane destroys adrenocortical cells
Adverse effects are common and include lethargy, weakness, vomiting, diarrhea,ataxia, head pressing, blindness, and iatrogenic hypoadrenocorticism
Incidence rate of side effects may be as high as 25–30%
Give with food to increase absorption
Monitor ACTH stimulation test cortisol levels every 1–6 months as a mainte-nance protocol
Mitotane does not suppress estradiol
Phenobarbital enhances the metabolism of mitotane, making it less effective
PDH:
Initial loading dose of 25–50 mg/kg PO divided and administered BID for
approximately 3–8 days
Observe for subtle changes in appetite or thirst
Repeat ACTH stimulation test until both basal and post-ACTH cortisol lev-
els are in the normal resting range (2–6μg/dL)
Maintenance dosage: 50 mg/kg per week divided and administered twice
weekly; dosage requirements may vary; dosage adjustments are based on
ACTH stimulation test results
If relapse occurs, as indicated by cortisol levels outside the normal rest-
ing range, reload for 5–7 days and increase weekly maintenance dose by
approximately 50%
Prednisone (0.2 mg/kg PO q24h) may be given during initial and subse-
quent loading periods