Diagnosis and treatment of atopy in cats - DVM
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Diagnosis and treatment of atopy in cats
Start with a good history


Testing and treatments

So you suspect you may have an atopic cat and you have treated empirically for ectoparasites, done your four-to-six-week hypoallergenic diet trial and historically the cat has been responsive to steroids. One other positive feature is that the cat is a male, neutered orange tabby with alopecic hocks.

The next step is treatment, which can involve steroids (if used short-term), antihistamines, immunotherapy or cyclosporine. Certainly if immunotherapy is elected, allergy testing via skin or serum is performed to identify which antigens need to be placed in the immunotherapy solution.

In my experience cats do very well on immunotherapy, and many times it's easier to administer a subcutaneous injection than it is to "pill" a cat.

The main drawback is response to therapy time, because immunotherapy can take many months to become effective. Antihistamines, steroids or cyclo-sporine can be used until the desired effect of immunotherapy kicks in.

If you're performing serum testing on cats using Heska's serum test, be sure the positive results correspond with the time of the year the cat is symptomatic. Also steroids and antihistamines can interfere with serum testing, so avoid those for as long as possible before testing. There is no specific down time for steroids because each individual differs with its steroid sensitivity. Some can be tested a month after discontinuation of steroids while others require several months off steroids to get an accurate test.

Cats administered megestrol acetate seem to take longer to be off this medication before positive testing occurs. Our Midwest office deals with specific pollen seasons. Fall is our best season for testing because the animal has just been exposed to spring, summer and fall pollens and year-round house dust mites. The latter can flare when the furnace is turned on and the days grow shorter (dust mites prefer darkness).

Once immunotherapy is started, be sure to tell the owner that if the cat ever seems more pruritic after an injection, they should stop injections and call you. That usually means the dose was too high, and you have caused the cat to become itchy. Some cats are pruritic after the first dose and require a further reduction in dilution right from the start.

If antihistamines, steroids or cyclo-sporine are chosen as the method of treatment, it isn't essential to know what exactly the allergens are that the cat is allergic to. Sometimes we will start with chlorpheniramine 4mg, -l tablet bid or clemastine l.34mg, tablet s-bid.

A small percentage of cats will respond to antihistamines only, which is great since you're avoiding steroids. The main drawback with antihistamines is their bitter flavor; excessive salivation may occur, which frightens some owners. Antihistamine tolerance can occur over time. A way to avoid it is to administer the antihistamine daily for three weeks to a month, off one week, then resume. Antihistamines should be used with caution in KCS, pregnant animals, glaucoma, heart disease, megacolon and seizure disorders.

Steroid alternatives

Most owners are referred to a veterinary dermatologist when steroids are no longer effective or underlying disease precludes their use (e.g., diabetes, heart disease).

Because house dust-mite allergy appears to be a common allergen in cats that exists year round, steroids are not an option.

In cases of seasonally affected cats, occasional steroid injections or oral prednisolone may be helpful but long-term use, as always, should be avoided, especially since there are other options.

Although not FDA-approved for use in cats, cyclosporine has become a nice alternative for steroids in treating atopic cats. The drug has been used since the 1970s for feline renal transplants at even higher doses than what is used in dogs (7.5-10mg/kg/day).

For atopic cats, we use 5mg/kg/day in cats or lower to start. I start at a low dose to avoid gastrointestinal side effects of vomiting or diarrhea. We use either the cyclosporine capsules or cyclo-sporine modified oral liquid 100mg/ml, and start at 0.1 mls or bid.

The drawback to the oral liquid is that the 50-ml bottle needs to be used within 60 days. The advantage to the liquid, in my opinion, is less gastrointestinal upset. Be sure to check toxoplasmosis status before starting the liquid because cyclosporine use can cause recrudescence of the disease.

It might be wise to avoid cyclosporine for outdoor cats, considering their potential of eating raw meat. I have seen some develop a mild neutropenia, so it is important to check complete blood counts and serum profiles before and routinely during use.

Once doing well on daily cyclosporine, it is possible to go to alternate-day dosing and even less than that. The advantage of cyclosporine is that it's not a steroid, can be administered orally and doesn't take several months to become effective as is the case with immunotherapy.

Atopy in cats is a reality and can be difficult to treat, let alone diagnose.

Thankfully, there are more options than just steroid injections, which fomerly were considered safe in cats.

Now we know that diabetes, demo-dicosis and heart disease can be associated with steroid use in the cat. Because atopy is for the life of the cat, steroid alternatives, which are much safer, are preferable and available.

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.


Source: DVM360 MAGAZINE,
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