If a patient's history supports a diagnosis of atopy and the above-noted differential diagnoses have been ruled out, skin
or serum testing is in order, particularly if the cat requires more than a minimum of corticosteroids annually. What constitutes
a minimum of corticosteroids is a relative question. I prefer not to administer more than three methylprednisolone injections
annually—and even less than that if there's any evidence of heart disease. Prolonged use of corticosteroids in cats may lead
to diabetes or heart disease, and now that immunotherapy and cyclosporine are excellent alternatives to corticosteroids, hopefully
those two diseases can be further prevented.
Become familiar with the laboratory you're using for the serum test, as each laboratory may have idiosyncrasies upon repeated
use (e.g., false positive results to molds). Most important, the serum test results should coincide with the time of year
the cat is affected. If the cat's signs are nonseasonal, the animal lives where there are set seasons, and the serum test
result is negative to house dust mites, then rethink the diagnosis. The serum or skin test results must match the time of
year the cat is affected. Otherwise, you won't be successful with immunotherapy.
Note, there's no definitive time that a patient should be off corticosteroids before testing. The timing depends on how long
the cat has been receiving a corticosteroid, how sensitive the cat is to the corticosteroid and the corticosteroid's duration
of activity. If the animal can go as long as possible off the corticosteroid before testing, you'll probably be OK.
Interpreting the serum test results can be challenging because not all cats register at the number the laboratory technician
may think is the cutoff point. In some patients, if a cat registers some response to all of a particular class of pollen (e.g.,
all grasses), the results may be significant.
As noted, effective treatment can include immunotherapy or administration of cyclosporine or a combination of these.
Immunotherapy usually takes six to 12 months. Instruct the owner that if the cat is pruritic after an injection, the client
needs to consult with you. We have seen cases in which cats were pruritic after the first injection and subsequently worse
on each injection thereafter, yet a veterinarian told the clients to continue administration.
If a cat is pruritic after the first injection, it's possible the beginning vial is too strong and needs to be diluted. After
an injection, you want to see the pruritus subsiding a bit and possibly increasing as the time approaches for the next injection.
If the cat was pruritic after the injection but the pruritus subsided as the week went on, this signals the dose was too high.
Sometimes during the patient's affected season, the dose should be reduced, particularly if what's in the injection is currently
Cyclosporine, which is now FDA-approved for cats (Atopica—Novartis), is a good alternative to corticosteroids for atopic cats.
Dosing can range from 2.5 to 7.5 mg/kg daily. The oral liquid can be given with or without food. Drug metabolism occurs in
the liver and intestines, with excretion in the feces and a small amount of an inactive metabolite in the urine. The drug
reaches steady state after one week.
Adverse effects include vomiting, regurgitation, weight loss, diarrhea, anorexia, lethargy and hypersalivation. In our practice
we perform a complete blood count, serum chemistry profile, urinalysis, FIV and FeLV tests and toxoplasmosis IgM and IgG before
starting the drug. Recrudescence of toxoplasmosis is possible in cats with cyclosporine levels > l,000 ng/ml, so it's a good
idea not to use cyclosporine in outdoor cats or cats ingesting raw meat. We start most of our patients at 2.5 mg/kg daily,
as we find many can be maintained on a daily dose of less than 5 to 7.5 mg/kg.
Once a cat has improved, we try to switch administration to every other day, and even less frequently later on in therapy.
Blood work should be performed yearly, as should a physical examination that includes checking that cat's body weight and
assessing for gingival hyperplasia, which appears to be more common in dogs receiving cyclosporine. The drug is useful in
diabetic cats that have become atopic, but blood glucose monitoring still should be performed.
With atopy in cats appearing to be more prevalent, it's helpful to know there are safe alternatives to the former use of long-acting
corticosteroids. Cats are not immune to the effects of corticosteroids as formerly thought, and educated pet owners may want
to seek alternatives to these drugs.
Dr. Jeromin is a pharmacist and veterinary dermatologist in private practice in Cleveland, Ohio. She is a 1989 graduate
of The Ohio State University College of Veterinary Medicine and an adjunct professor at Case Western Reserve University's
College of Medicine in Cleveland.