Getting to the source of the itch

By Matthew Kearns, DVM

My last column introduced the seasonal allergies that our pets can suffer from, also known as atopic dermatitis. This second part of the two-part article focuses more on the treatment of atopic dermatitis. The treatments we will discuss only focus on systemic medications. It does not include supplements, topical creams/powders/sprays, medicated shampoos/conditioners, etc. I’ll make sure to cover that in the future. 

Now, if we remember from the first part of the article, atopy is defined as, “a genetic predisposition to develop a sensitivity to allergens (proteins in the environment).” The body develops antibodies against these allergens (primarily IgE) and, once a threshold is reached, the IgE antibodies trigger signals to certain white blood cells called basophils and mast cells to release inflammatory chemicals into the system (primarily histamine). This release of histamine triggers all the itch and secondary skin and ear infections that frustrate both pet owners and veterinarians. What is out there to help with the problem?

Antihistamines

Antihistamines block the histamine receptors on nerves, vessels, muscle cells and the lining of stomach and small intestine. They are readily available without a prescription and safe so they can be an excellent first choice. Unfortunately, antihistamines do not block the release of histamine from basophils and mast cells but rather block the receptors on the cells of the organs they affect.  

Now, you can’t block every receptor with medication so it very much depends how severely the individual pet responds to an atopic, or allergic, reaction. Pets with mild allergies will do well with antihistamines. However, pets with more severe forms of allergies either do not respond well or respond temporarily to antihistamines and eventually need a stronger medication.

 Corticosteroids 

Corticosteroids, glucocorticoids, or “steroids,” as they are sometimes referred to, are all cortisone derivatives. Systemic cortisone medications are prescription only. However, corticosteroids are inexpensive and very effective at treating atopic diseases. They block the production of all cytokines (mediators of inflammation) and, if it wasn’t for the side effects, would be a magic bullet. Short-term use is relatively safe and very beneficial. Side effects include drinking/urinating more, eating more and panting. 

However, long-term side effects include gastrointestinal upset/possible ulcers, a suppressed immune system, diabetes mellitus, liver damage, pancreatitis, thromboemboli (blood clots), increased risk of urinary and other types of infections, lethargy and, sometimes, aggression. 

We, as veterinarians, try to transition patients with chronic, recurrent skin and ear problems to other, safer long-term medications.

Immunomodulators 

These prescription medications are more effective than antihistamines and safer to use long term than corticosteroids. Medications like Atopica (cyclosporine) and Apoquel (oclacitinib) block a specific receptor and prevent specific cytokines associated with the allergic itch. These are newer medications with minimal side effects and safe to use long term but are more expensive than antihistamines or corticosteroids.

Biologic therapy 

This is the newest kid on the block. Biologic therapy uses the body’s immune system to target cytokines, or chemicals that induce inflammation. Cytopoint (lokivetmab) is a once monthly injection that induces your dog’s immune system to produce antibodies against a specific class of cytokines called interleukins. Interleukins have been linked to the itch in allergic or atopic dermatitis.

Multiple factors play into what medication we choose: severity, age of pet, pre-existing disease and cost of medication. I hope pet owners will start the discussion with their own vet as to which medication is best for their pet.  

Dr. Kearns practices veterinary medicine from his Port Jefferson office and is pictured with his son Matthew and his dog Jasmine.