FDA approves updated US label for Zenrelia

Photo: Reddogs/Adobe Stock

The FDA has approved an updated US label for ilunocitinib tablets (Zenrelia; Elanco), removing language about the risk of fatal vaccine-induced disease associated with the medication from modified live virus vaccines. The revision to the label comes after the federal agency reviewed additionally submitted data, according to an announcement by Elanco.¹

The immunosuppressant, first approved in September 2024, is a non-selective Janus kinase (JAK) inhibitor administered once a day for the control of pruritus associated with allergic dermatitis and the control of atopic dermatitis in dogs of at least 12 months of age.²

When the medication was first launched, the US label contained language based on lab study results in unvaccinated dogs given 3 times the approved dose of Zenrelia. According to Elanco, an outbreak of concurrent diseases occurred during the study, “complicating interpretation of the results.”¹

In the study, some treated dogs developed “fatal vaccine-induced adenoviral hepatitis (liver inflammation) and pancreatitis (inflammation of the pancreas) in one dog; and infectious enteritis (inflammation of the intestines) in one dog,” the FDA wrote in its initial 2024 approval summary.² Other dogs failed to mount an adequate response to rabies and distemper vaccines, as Zenrelia works partially by suppressing the immune system.²

Still, in its initial approval last year, the FDA noted that “Zenrelia is safe and effective when used according to the label."²

Having evaluated additionally submitted data, the FDA now states that “the totality of evidence supports removal of the risk of fatal vaccine-induced disease from modified live virus vaccines from the labeling.”

However, a Boxed Warning on the label advising “discontinuation of Zenrelia for at least 28 days to 3 months prior to vaccination and withholding Zenrelia for at least 28 days after vaccination due to the risk of inadequate immune response to vaccines” still remains.¹

“When initiating treatment with Zenrelia, refer to label directions. Zenrelia should only be used in dogs that are up to date on vaccinations, at least 12 months old and free from serious infection,” noted Elanco.¹

Dogs on Zenrelia should also be monitored for infections, as the medication increases the chances of developing an infection. During clinical studies, researchers observed benign and malignant neoplastic conditions in dogs. Common adverse effects associated with the medication are vomiting, diarrhea, and tiredness.

The medication has not been tested in breeding, pregnant, or lactating dogs or alongside other immunosuppressive therapies such as glucocorticoids or cyclosporine.

"We appreciate the FDA's commitment to reviewing the latest submitted scientific data to ensure that the label is reflective of the totality of evidence," Ellen DeBrabander, PhD, executive vice president of research & development at Elanco, said in Elanco’s announcement.¹

In addition to the US, the drug has also become available in the European Union, Great Britain, Brazil, Canada, and Japan. According to Elanco, more than half a million dogs globally have been treated with Zenrelia.

References

1. Elanco announces FDA approves improved Zenrelia™ (ilunocitinib tablets) label, removing vaccine-induced disease language. News release. Elanco. September 23, 2025. Accessed September 23, 2025. https://www.prnewswire.com/news-releases/elanco-announces-fda-approves-improved-zenrelia-ilunocitinib-tablets-label-removing-vaccine-induced-disease-language-302564189.html
2. FDA approves new treatment for allergic skin conditions in dogs. News release. U.S. Food and Drug Administration. September 19, 2024. Accessed September 23, 2025. https://www.fda.gov/animal-veterinary/cvm-updates/fda-approves-new-treatment-allergic-skin-conditions-dogs