Controlling Polyuria in Addison's Dogs Treated with Prednisone

I have a 3-year old, F/S Chihuahua, who was recently diagnosed with Addison's disease. She is doing great on injections of desoxycorticosterone pivalate (DOCP; Percoten V) and oral prednisone. She weighs 14 pounds (6.4 kg) so I'm administering 0.5 ml (12.5 mg) of Percoten V each month and 2.5 mg of prednisone every other day.

Recently, the owner noticed that on the days that she was giving the prednisone, the dog was leaking urine while asleep.We decreased dose of predisone to 1.25 mg twice weekly, but still leaking urine on the days given prednisone.

The dog may need a workup for urinary incontinence, but assuming that all checks out okay, she might be sensitive to the oral glucocorticoid. Any thoughts on a different steroid in place of the prednisone? Would dexamethasone work better?

My Response:

In dogs with hypoadrenocorticism (Addison's disease), the daily maintenance dose for prednisone (or prednisolone) to replace the missing glucocorticoids is approximately 0.1-0.2 mg/kg/day (1-4). Many dogs are very sensitive to the effects of chronic glucocorticoid replacement, and polyuria and polydipsia are common complaints (4).

In these dogs that show side effects related to prednisone replacement therapy, we start by lowering the daily maintenance dose down to the lower end of the recommended range (i.e., closer to 0.1 mg/kg/day). So this calculates out to be only 0.6 mg per day for your patient — about half the dose of what you are giving.

In small dogs like this, there is no way to use the standard 5-mg tablets of prednisone or prednisolone to administer the low dose needed. I'd either switch to a liquid prednisolone formulation (e.g., PediaPred) or get 1-mg prednisone tablets and then try 0.5-0.6 mg per day. Your other option would be to use cortisone acetate, but that drug is best given twice daily for replacement therapy (0.5 mg/kg, BID or around 2.5 mg BID in this dog).

For replacement therapy, we want to give a short-acting glucocorticoid (prednisone, prednisolone, or cortisone).  Because dexamethasone is a very potent long-acting steroid, use of this preparation isn't appropriate for long-term use in dogs with Addison's disease.

References:

1. Kintzer PP, Peterson ME. Primary and secondary canine hypoadrenocorticism. Veterinary Clinics of North America Small Animal Practice 1997;27:349-57. 
2. Kintzer PP, Peterson ME. Treatment and long-term follow-up of 205 dogs with hypoadrenocorticism. Journal of Veterinary Internal Medicine 1997;11:43-49. 
3. Klein SC, Peterson ME. Canine hypoadrenocorticism: part II. Canadian Veterinary Journal 2010;51:179-184.
4. Peterson ME: Treatment of hypoadrenocorticism: Treatment pitfalls and issues. Proceedings of the ACVIM Regional Education Course on Endocrinology. 2010