Atopy in Cats
Dr. Mark Thompson
Two primary forms of treatment for atopy are available: drug treatment and immunotherapy. The ideal treatment for most moderately and severely affected animals is some combination of both types of treatment. Drug therapy relieves the symptoms of atopy but does nothing to treat the underlying allergy itself. Most cats with atopy are young and may require years of therapy. Treatments for atopy may include one or more of the following: Antihistamines are much less helpful in atopic cats than they are in humans. Antihistamines help only 25 to 30 percent of atopic cats, but often are tried first because they have fewer adverse effects than do the cortisone-like drugs (i.e., corticosteroids). Some animals respond better to one antihistamine than to others, and your veterinarian may try 2 or 3 different types of antihistamines before concluding that they are not helpful in a given cat.
Fatty acid supplements may relieve itchiness (i.e., pruritus) by modulating the immune response. Certain fatty acids such as eicosapentanoic acid (found in fish oil) help change the chemical composition of cell membranes and ultimately the types of chemical mediators (i.e., prostaglandins) produced during the allergic response, resulting in a milder response. Like antihistamines, these products are not helpful in all affected animals, but they are very safe. Some cats that do not respond well to antihistamines may respond to a combination of antihistamines and fatty acids.
Secondary bacterial infections are common in cats with allergic skin disease. Therefore, cats with atopy occasionally need antibiotics to treat complicating pyoderma. Yeast infections of the skin and ear also have to be treated occasionally.
Shampoo therapy may be very helpful in managing itchiness (i.e., pruritus) caused by atopy. Shampoos that contain colloidal oatmeal are soothing and moisturizing, and can be used frequently without drying the skin. Some oatmeal-based shampoos contain topical anesthetics or topical corticosteroids that are very safe and further help reduce itchiness (i.e., pruritus).
When the above treatments are no longer effective, corticosteroids such as prednisone may be used. This class of drugs is very effective in atopic animals. Unfortunately, however, these drugs have many potential adverse effects that restrict their long-term use. Cats can experience severe adverse effects if corticosteroids are not used carefully. Examples of the adverse effects of corticosteroids include increased water consumption (polydipsia) and urinations (polyuria), increased appetite and food intake (polyphagia) leading to obesity, suppression of the immune system leading potentially to secondary infections, irritation of the stomach, alterations in liver function tests, and suppression of normal adrenal gland activity.
Short-acting, orally-administered corticosteroids are safer than long-acting injectable corticosteroids because the former can be cleared rapidly from the animal's body in the event of adverse effects. Long-acting injectable corticosteroids should be reserved for use in cats that resist administration of oral medications.
Immunotherapy (hyposensitization, desensitization, allergy shots) theoretically is the ideal form of treatment for atopy, and is recommended for cats that cannot be managed safely and effectively with symptomatic therapy. The exact mechanism by which immunotherapy works is not well understood, but the goal is to induce tolerance by the immune system to allergens to which the animal is sensitive. This technique is effective in 60 to 80 percent of atopic cats.
An extract of the allergens selected by allergy testing is prepared. Initially, a small amount is injected frequently (every 1 to 2 days) and the dosage gradually increased. Due to the frequency of injections, your veterinarian usually will show you how to administer the injections at home. Once the cumulative dose reaches a certain level, the injection interval is slowly increased until injections are given every 2 to 3 weeks. The interval may then be maintained for a relatively long period of time. Improvement is gradual and your cat may not benefit markedly for the first 3 to 6 months of immunotherapy. Antihistamines, fatty acid supplements and soothing shampoos may be used while immunologic tolerance develops.