Zenrelia is a Janus Kinase (JAK) inhibitor approved for the treatment of pruritus associated with allergic dermatitis in dogs and for the treatment of the clinical manifestations of atopic dermatitis in dogs. It is an oral tablet, dosed once daily at 0.6-0.8 mg/kg.

Ilunocitinib is a JAK inhibitor that inhibits the function of a variety of pruritogenic and pro-inflammatory cytokines, as well as cytokines involved in allergy which are dependent on JAK enzyme activity.

Zenrelia is rapidly absorbed after oral administration and begins to work quickly, with visible improvements in itch after the first dose.^*

*Forster S, et al. Comparative efficacy and safety of ilunocitinib and oclacitinib for the control of pruritus and associated skin lesions in dogs with atopic dermatitis. Veterinary Dermatology. 2025;36:165-176 

The dose of Zenrelia has been optimised for once daily dosing (every 24 hours) from the start. It has a relatively short half-life within the bloodstream and does not accumulate in the body, meaning that if dosing is stopped the drug is cleared from the dog’s body within a few days. This facilitates starting and stopping treatment as needed to control allergic itch and inflammation or while performing a diagnostic food trial.

Yes. Food allergies fall under the umbrella of ‘allergic dermatitis’. Dogs with food allergies were included in the allergic dermatitis clinical field trial.* Dogs included in the clinical field trial could have one or more of these conditions.

*Forster, S, et al. (2025). Efficacy and Field Safety of Ilunocitinib for the Control of Allergic Dermatitis in Client-Owned Dogs: A Multicenter, Double-Masked, Randomised, Placebo-Controlled Clinical Trial. Veterinary Dermatology, 1-13.

Yes. Zenrelia can be used to control symptoms during a food trial and stopped toward the end of the food trial to see if symptoms return. Zenrelia is rapidly absorbed after administration, has a relatively short half-life in the blood, and does not accumulate; meaning it begins working quickly and is cleared from the dog’s body within about 24 hours after stopping treatment. This facilitates starting and stopping treatment as needed to control symptoms while doing a food trial or other diagnostic trial in dogs with allergies.

Zenrelia is supplied as a scored tablet in four different strengths, allowing for accurate dosing of dogs as small as 3kg. Zenrelia is available in boxes containing 30 tablets in blister packs.

No. Zenrelia tablets are unflavoured.

Zenrelia can be administered with or without food. It is recommended that an individual dog is dosed in a consistent manner i.e. regularly either with or without food.

There is no labelled limit to the duration of Zenrelia use. One indication for Zenrelia is atopic dermatitis which is a chronic condition.

There are no specific requirements on the Zenrelia label for bloodwork prior to starting treatment. Establishing a baseline prior to starting a dog on any long-term medication could be considered best practice and would be done at the discretion of the veterinarian.

Zenrelia is rapidly absorbed, with maximum blood concentration reached in 1-2 hours after administration, so if a dog vomits after that time it is likely unnecessary to give Zenrelia again until the next day. If a dog vomits within 20 minutes of receiving Zenrelia then consider redosing.

Zenrelia should be given once daily in accordance with the label dose. If a dog continues to itch after receiving Zenrelia it’s important to revisit the diagnostic workup and ensure other causes for itch have been ruled out, including bacterial and fungal skin infections, ectoparasites (fleas), food sensitivities, etc.

Use with caution in combination with glucocorticoids, cyclosporin, or other systemic immunosuppressive agents, as the use of Zenrelia in combination with these types of products has not been evaluated.

No drug interactions were observed in field studies where ilunocitinib was administered concomitantly with veterinary medicinal products such as endo- and ectoparasiticides, antimicrobials, vaccines and non-steroidal anti-inflammatories.

The safety of Zenrelia has not been investigated in dogs weighing less than 3 kg.

The safety of Zenrelia has not been investigated in dogs younger than 12 months of age.

Zenrelia is labelled for use in dogs only; use in other species would be considered off-label use.

The safe use of Zenrelia has not been evaluated in breeding, pregnant, or lactating dogs.

Although Zenrelia and Apoquel are the same class of drug (JAK inhibitors) with the same indications for treatment, they contain different active ingredients. Apoquel® contains oclacitinib and Zenrelia contains ilunocitinib. JAK inhibitors regulate the inflammatory response to allergens by binding to multiple Janus Kinase (JAK) enzymes and interfering with cell signalling.

The "generation" terminology for JAK inhibitors is based on the historical development of these drugs in human medicine. “First generation” and “Second generation” JAK inhibitors differ on how selective they are for target JAK enzymes in in vitro testing. Initially, it was hypothesised that a JAK inhibitor’s efficacy and safety could be predicted based on its selectivity profile, established using in vitro laboratory assays. However, experience in human medicine has demonstrated that these in vitro laboratory assays do not predict clinical efficacy and safety variations between JAK inhibitors, so head-to-head clinical trials remain the gold standard for comparison of safety and efficacy.*

*Bonelli M, Kerschbaumer A, Kastrati K, et al. Selectivity, efficacy and safety of JAKinibs: new evidence for a still evolving story. Annals of the Rheumatic Diseases. 2024 Feb 1;83(2):139-60.

Choy EH. Clinical significance of Janus Kinase inhibitor selectivity. Rheumatology. 2019 Jun 1;58(6):953-62.

Virtanen A, Palmroth M, Liukkonen S, et al. Differences in JAK Isoform Selectivity Among Different Types of JAK Inhibitors Evaluated for Rheumatic Diseases Through In Vitro Profiling. Arthritis &Rheumatology. 2023 Nov;75(11):2054-61