How to Adjust the Glucocorticoid Dose in Dogs Treated for Addison's Disease
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| Zoe, a female Rat Terrior with Addison's disease |
She is active and playful but is always famished. Her water intake has also increased on the medication, but she isn't showing any incontinence.
My major concern is that she has lost her hair on all four legs and belly, and now it is progressing up her shoulders, hind quarters, and to her head!
Her lab tests are within normal range according to her vet, who wants to take a wait and see approach. I thought she may be getting too much prednisone, but my vet is afraid to cut back for fear of her ”crashing” and developing an adrenal crisis.
Any thoughts on this? Zoe could sure use the help before all the other dogs start teasing her!
My Response:
Based on the clinical features of increased appetite, increased thirst, and hair loss, it is most likely that Zoe is being overdosed with the prednisone and has developed iatrogenic Cushing's syndrome (glucocorticoid excess).
In support of that, the daily maintenance dose of prednisone or prednisolone in dogs with Addison's disease is only 0.1-0.2 mg per kg per day. So at 8 kg (Zoe's body weight), that calculates out to 0.8 mg to 1.6 mg per day. This is only 15-30% of the dose that she is now receiving every day. When you think about that, it's no wonder that she is showing signs of glucocorticoid (prednisone) excess!
Remember that the adrenal glands in dogs with Addison's disease have failed so we must replace the missing hormones. These dogs will require lifelong replacement with both a mineralocorticoid (e.g., Percoten-V) and glucocorticoid (e.g., prednisone) hormone. Both the mineralocorticoids and glucocorticoid dosages must be individualized for that particular dog.
The dosage of the mineralocorticoids can best be determined by monitoring the serum electrolyte concentrations (sodium, chloride, and potassium); the dosage is increased to decreased, as needed to normalize the circulating electrolyte concentrations.
Prednisone (or prednisolone), a common glucocorticoid used to treat dogs with Addison's disease, is ideally started at physiological dosages (0.1-0.2 mg/kg/day). This dosage should be adjusted up or down as needed, as some dogs show exquisite sensitivity to the adverse prednisone’s effects. The amount of prednisone that enhances the dog’s well-being (normal activity level and appetite) but prevents side effects (increased thirst, panting, polyphagia, hair loss) may be very small.
If a dog's serum electrolytes are normal on Percorten replacement therapy, dogs with Addison's disease aren't going to develop serious adrenal crisis, even if the prednisone dosage is lowered too much for a day or two.
My Bottom Line:
Your dog is receiving too much glucocorticoid supplementation. With time, even a mild overdose will lead to signs of iatrogenic Cushing's syndrome, which may include hair loss, increased thirst and urination, and increased appetite. I'd taper the dose down to 1 mg per day over the next couple of weeks. The prednisone is available as a 1-mg tablet, which would make dosing much more convenient.
If the hair loss doesn't resolve after two to three months, I'd recommend that your veterinarian check a serum thyroid panel. Some dog's with Addison's disease will also develop concurrent hypothyroidism, which commonly leads to hair loss in dogs.
References:
- Church DB. Canine hypoadrenocorticism. In: Mooney CT, Peterson ME, eds. BSAVA Manual of Canine and Feline Endocrinology. 3rd ed. Quedgeley, Gloucester: British Small Animal Veterinary Association, 2004; 172-180.
- Kintzer PP, Peterson ME. Treatment and long-term follow-up of 205 dogs with hypoadrenocorticism. J Vet Intern Med 1997;11:43-49.
- Klein SC, Peterson ME. Canine hypoadrenocorticism: part I. Can Vet J 2010;51:63-69.
- Klein SC, Peterson ME. Canine hypoadrenocorticism: part II. Can Vet J 2010;51:179-184.
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