By Carlo Vitale, DVM, DACVD
Corticosteroids are among the most used and misused medications in veterinary medicine. They exert a powerful, reliable, and rapid effect, and there is no viable, more effective therapeutic alternative in animals with certain skin conditions. Topical and oral corticosteroid therapies are considered the first choice for treatment of acute and chronic inflammatory skin diseases, particularly allergic dermatitis. In addition, they aid in the inflammation associated with some types of infections, primarily Malassezia dermatitis and otitis.
Using oral corticosteroids
As a review, the oral corticosteroids available for dogs are listed in Table 1 along with their relative potencies, half-life, and relative mineralocorticoid effects. As you can see from the table, these drugs’ half-life becomes much longer as the potency increases. This is important from a clinical standpoint because many patients which are treated for more than two to three weeks with oral corticosteroids experience side effects.1 To minimise these effects, clinicians should use an alternate-day protocol when administering oral corticosteroids longer than two weeks.
The incidence of side effects—either annoying or more serious—increases as the potency of the corticosteroid increases. Some controversy surrounds the use of oral triamcinolone in regard to its potency and half-life. To be conservative, it is best to assume that oral triamcinolone has a greater potency than prednisone or prednisolone and has a longer biologic half-life—closer to 36 hours. Therefore, practitioners should reserve the use of oral triamcinolone in dogs for treatment of serious refractory skin diseases. Oral dexamethasone should be used in canine cases only if no other treatment has been successful and the owners have been warned about the potential serious side effects, or the owners are debating the pet’s quality of life (i.e., they are considering euthanasia).
The mineralocorticoid effects of corticosteroids are responsible for increased water consumption, subsequent increased urine output, and potential urinary incontinence. Prednisone and prednisolone exert a slightly stronger mineralocorticoid effect than methylprednisolone. Therefore, methylprednisolone may be used instead of prednisone or prednisolone in cases of undesirable increases in water consumption and urine output.