New canine itch medication: Interpreting label claims and warnings

In mid-September, Elanco Animal Health announced their new animal drug Zenrelia (ilunocitinib tablets) were approved by the FDA for the treatment of allergic and atopic dermatitis in dogs. The drug, an oral JAK inhibitor in the same family as Apoquel (oclatinib tablet, zoetis), is labeled to be given once daily to dogs over twelve months of age when prescribed by a veterinarian.

In their announcement, Elanco made several comparisons between their drug and market rival Apoquel. Zenrelia was shown in studies to be “at least as effective” as Apoquel according to Elanco, and to result in “clinical remission of itch” in 77% of dogs, compared to 53% with Apoquel. The manufacturer also claims Zenrelia causes less rebound itching when transitioning from twice-daily to once-daily dosing after 14 days. They also highlight its once-daily dosing as a cost-saving benefit for pet owners.

A dermatologist’s perspective

Andrew Simpson, DVM, MS, DACVD, a veterinary dermatologist at VCA Aurora Animal hospital, sees a need for additional treatment options for dogs with allergic dermatitis.  He pointed to the “major innovations” in the treatment of canine allergic dermatitis with the availability of drugs like Apoquel and Cytopoint that avoid steroid side effects help many dogs experience significant itch relief. “Nevertheless, as with any clinical disease,” he said, “there is not a one-size-fits-all or a panacea for allergic dermatitis.”

Simpson still reports seeing a small number of dogs who don’t respond well to the currently available therapies, which is where a new drug may be helpful. “The clinical pictures or phenotype of an allergic disease may look quite different between patients,” he said. Even when the signs are the same, however, not every dog will respond to the same treatment approach, he explained. “You may see five to six dogs with the same exact clinical presentation of allergic dermatitis in one day, but each case may require a different approach to managing their disease.”

Understanding “clinical remission”

Although he has not had an opportunity to treat patients with Zenrelia yet, Simpson offered some insight into the claim of clinical remission made by the manufacturer that may help other veterinary professionals make their own decisions about adding this new drug to their arsenal.

The term remission may cause confusion, as in other diseases it is often associated with an absence of signs of disease resembling a cure. Simpson notes that the term “clinical remission” has not typically been used in veterinary medicine with reference to allergic dermatitis or itch, although it has been in human medicine for similar conditions.

While the definition of clinical remission in conditions such as autoimmune diseases or neoplasia may suggest an absence of evidence of disease, Simpson recommends a different definition for allergic dermatitis.  “The definition of clinical remission of itch is defined as a pruritus visual analogue score (a research-based scoring tool evaluated by the pet owner) of less than 2, which is equivalent to that of a normal dog without allergies,” he explained.

It is important to note that even though the patient’s itch level may be indistinguishable from that of a non-allergic dog, that does not equate to a cure.  Simpson states that atopic dogs “are not ever cured of their disease but rather managed.” He recommends the phrase “control of disease” as opposed to clinical remission to describe the potential effects JAK inhibitors such as Zenrelia.

Important safety precautions

The Zenrelia label and prescribing information include a black box warning regarding the use of the drug in conjunction with vaccines in dogs. A vaccine response study noted immunosuppression, inadequate immune response to vaccines, and risk of fatal vaccine-induced disease in some of the puppies taking Zenrelia at the time of vaccination. As a result, the manufacturer recommends discontinuing Zenrelia “for at least 28 days to 3 months prior to vaccination” and withholding Zenrelia “for at least 28 days after vaccination.” This is in addition to only administering the drug to dogs aged 12 months and older.

As with other JAK inhibitors, the use of Zenrelia can also increase the risk of opportunistic infections and neoplasia. Infections such as demodicosis, interdigital furunculosis, coccidiosis, and pneumonia were identified by the manufacturer as safety risks for patients taking this drug. Patients who have a preexisting infection are also at risk for exacerbation of the infection with the use of Zenrelia. Careful case selection and close monitoring are very important for all patients when this medication is prescribed.

Further reading

2023 AAHA Management of Allergic Skin Disease in Dogs and Cats Guidelines and Toolkit

Zenrelia prescribing instructions

Zenrelia for vets website

Dear Veterinarian Letter from the FDA on the use of Zenrelia

Pruritus Visual Analog Scale (Canine)

 

Photo credit: MaRussya/iStock via Getty Images

Disclaimer: The views expressed, and topics discussed, in any NEWStat column or article are intended to inform, educate, or entertain, and do not represent an official position by the American Animal Hospital Association (AAHA) or its Board of Directors.