Q. Please review preferred treatment for pituitary-dependent hyperadrenocorticism in dogs.

A. Dr. Edward C. Feldman at the 2005 American College of Veterinary Internal Medical Forum in Baltimore gave a lecture on treatment of hyperadrenocorticism in dogs. Some relevant points in this lecture are provided below.

The preferred medical therapy for pituitary-dependent hyperadrenocorticism in dogs is either lysodren or trilostane therapy.

Lysodren (o,p'-DDD) therapy is initiated at home with the owner administering 25 mg/kg, given twice daily. Glucocorticoids are not routinely administered and are not routinely dispensed. Rather, the owner should receive thorough instructions on the actions of o,p'-DDD. Then, the owner is instructed to begin reducing their dog's food allotment by one-third beginning the day before o,p'-DDD is begun. Therapy is often started on Sundays. In other words, owners give their dog one-third of its normal food allotment each morning and again each afternoon, beginning on a Saturday. This should make the typical polyphagic dog ravenous. No dog with a poor appetite should ever receive this drug! Lysodren administration should be stopped when

1) The polydipsic dog's daily water consumption approaches 60 ml/kg.
2) The dog simply takes longer to consume a meal and certainly if it develops partial or complete inappetence.
3) vomiting,
4) diarrhea,
5) unusual listlessness.

Any of these signs is an indication for the owner to stop daily o,p'-DDD therapy and have the dog examined by the veterinarian. The single most reliable and consistent indicator for stopping the induction phase of therapy is appetite. Any reduction in appetite indicates that the induction phase of therapy has been completed. The water intake in polydipsic dogs may decrease in as few as two days or in as long as 35 days (average is five to 14 days).

Lysodren is quite successful in eliminating signs of hyperadrenocorticism. This should be coupled with close communication between owner and veterinarian. Either the veterinarian or a technician should call the owner every day beginning with the second day of therapy. The owner should be impressed with the veterinarian's concern and will observe the animal closely. The owners are instructed to feed their dogs two small meals each day. The dog's appetite should be observed prior to each o,p'-DDD administration. If food is rapidly consumed, medication can be given. If food is consumed slowly, incompletely or not at all, the medication should not be given until the veterinarian is notified and an ACTH-response test is performed. In addition to making daily phone calls, the veterinarian should see the dog eight to nine days after beginning therapy. At this time, a thorough history, physical examination and an ACTH-response test should be performed. Dogs that have responded clinically to the medication (or if the owner is not certain about response) should have further therapy withheld until results of the ACTH-response test can be evaluated.

The goals of therapy with o,p'-DDD are to achieve resolution of the clinical signs and an ACTH-response test that is suggestive of relative hypoadrenocorticism. Successful response to o,p'-DDD is indicated by pre- and post-ACTH plasma cortisol concentrations greater than 1.5 micrograms per dl and less than 5 micrograms per dl.

Maintenance therapy for lysodren

The maintenance phase of therapy with o,p'-DDD may be initiated once a hypoadrenal response to ACTH is obtained. If the dog with hyperadrenocorticism has a normal or exaggerated response to ACTH following the initial eight to nine days of o,p'-DDD therapy, daily medication should be continued. While quite unusual, it is continued for three to seven additional days. ACTH response tests should be repeated every seven to 10 days until a low post-ACTH plasma cortisol concentration is achieved. It is important to emphasize that each dog should be treated as an individual. There appears to be no reliable method of predicting the length of time required for a response or the amount of o,p'-DDD therapy except to state that most dogs respond in five to nine days. It is unusual for a dog to require more than nine consecutive days of o,p'-DDD. Approximately 20 percent of dogs with hyperadrenocorticism are not polydipsic. They, too, can and should be treated by their owners at home.