GLUCOCORTICOID EFFECTS ON FELINE PATIENTS
In general, cats tolerate glucocorticoids well, and adverse effects seem to occur less frequently in cats than in other species.
Clinical signs of adverse effects
In one study, daily immunosuppressive doses of either prednisolone or dexamethasone for two months caused no clinical signs
of adverse effects with the exception of possible mild polyuria and polydipsia (PU/PD) in 13 of 14 treated cats.15 One cat in the study developed anorexia, pruritus, icterus, and medial curling of the pinna, some of which were suspected
to be caused by the glucocorticoid. A separate study in four cats treated with methylprednisolone acetate at 5 mg/kg given
subcutaneously once a week for a month also failed to detect any adverse clinical effects.11 In contrast, most dogs receiving even short courses of glucocorticoids quickly develop PU/PD, polyphagia, and panting, with
additional adverse effects common during treatment for longer periods.9 Both of these studies support the clinical experience that suggests glucocorticoid-induced adverse effects are less common
in cats, although marked and unique problems still may occur.
Effects on the complete blood count
One important method by which glucocorticoids produce their beneficial effects is through inhibiting immune cell recruitment
to inflammation sites. Neutrophils are prevented from attaching to blood vessels and entering tissues, while lymphocytes are
redistributed to other compartments such as the bone marrow or lymph nodes. These changes can be reflected in the complete
blood count (CBC) and often are termed the stress leukogram or leukemoid response. In most species, a stress leukogram involves mature neutrophilia, lymphopenia, and eosinopenia. Lymphopenia and eosinopenia
are seen in about 80% of dogs with hyperadrenocorticism, with 20% to 25% having increases in the total white blood cell count.16 In response to glucocorticoid administration, monocytes are increased in dogs but decreased in people.17
In the few studies that examined the typical stress leukogram in cats, the response seems more variable. Cats with naturally
occurring hyperadrenocorticism displayed neutrophilia only 53% of the time, while lymphopenia and eosinopenia are seen 56%
and 58% of the time, respectively.18 In two separate studies in which cats were treated with prednisone at 2 mg/kg once a day for two weeks, no effect was seen
on the number of white blood cells; however, the low bioavailability of prednisone may have affected these results.19,20 In contrast, after three doses of dexamethasone at about 0.4 mg/kg once a day, cats did develop a significant increase in
leukocytes.21 Another study showed that after two months of daily immunosuppressive doses of either prednisolone or dexamethasone, cats
developed significant increases in white blood cells, neutrophils, and monocytes, although overt instances of leukocytosis,
neutrophilia, or monocytosis were rare.15 Significant decreases in lymphocytes and eosinophils also were seen in this study, and lymphopenia was the most common CBC
abnormality, present in 57% of the cats.15
Effects on the serum chemistry profile
Several studies reveal the effects of glucocorticoids on the feline serum chemistry profile.11,15,22 Increases in albumin concentrations were documented in all of these studies. In one study, hyperalbuminemia was the most
common glucocorticoid-induced biochemistry abnormality. Increases in total protein concentrations, but not globulin concentrations,
were present concurrently.15 It has been suggested that glucocorticoids may directly affect albumin synthesis in cats, as has been documented in other
species.15,23 Increased total calcium concentrations also were shown, although this could have been related to the increased albumin concentrations
to which circulating calcium is bound.
Increases in serum glucose concentrations were also common abnormalities,15 with up to 75% of cats demonstrating hyperglycemia after as little as a single 5-mg/kg subcutaneous injection of methylprednisolone
acetate.11 Concurrent increases in serum fructosamine concentrations in one study of 14 cats support the theory that true hyperglycemia,
rather than transient stress-induced hyperglycemia, commonly may occur in glucocorticoid-treated cats.15
Increased alkaline phosphatase (ALP) and alanine transaminase (ALT) activities, which commonly are seen with glucocorticoid
use in dogs, are seen inconsistently in cats. One study did show mild increases in the activities of these enzymes.22 Other studies found no change in the overall mean activity of either ALP or ALT secondary to glucocorticoid use, although
there was wide interindividual variation, with some cats showing marked increases of one or both of these enzymes.11,15
Other abnormalities found repeatedly in these studies on the effects of glucocorticoids on the feline chemistry profile included
increases in cholesterol concentration and amylase activity, along with decreases in phosphorus, chloride, and creatinine
concentrations.11,15,22
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