FDA approval puts Numelvi into the canine itch market

Merck Animal Health’s atinvicitinib tablets, marketed as NUMELVI, have now entered the canine itch market after FDA approval on February 25, 2026, for control of pruritus associated with allergic dermatitis in dogs 6 months of age and older. The approval gives veterinarians a new oral Janus kinase, or JAK, inhibitor option in a category that has drawn close attention since Elanco’s Zenrelia reached the U.S. market in September 2024 with label language tied to vaccine-response concerns. Merck is positioning NUMELVI as the first veterinary “second-generation” JAK inhibitor, with spring 2026 U.S. availability expected for clinics and hospitals. Company and trade coverage have also emphasized practical positioning points, including once-daily dosing, use in dogs starting at 4.4 pounds, and the claim that most patients will need only one tablet or half a tablet. (merck.com)

Why it matters: For veterinary professionals, this is less about one more dermatology SKU and more about a potentially meaningful shift in how allergic itch is managed in younger dogs and in patients whose vaccine timing complicates treatment planning. FDA materials for NUMELVI indicate dogs treated at three times the maximum labeled dose for 84 days still mounted protective vaccine responses in the company’s study, a point Merck has emphasized in contrast to the earlier Zenrelia label history. In practice, that could matter for case selection, workflow, and conversations with pet parents weighing Apoquel, Cytopoint, Zenrelia, or now NUMELVI for chronic allergic disease. It also lands in a broader practice environment where teams are already thinking hard about affordability and adherence, including how clients pay for long-term care and whether insurance or financing reduces treatment friction. (animaldrugsatfda.fda.gov)

What to watch: Watch for the full U.S. launch this spring, early clinician uptake, and whether dermatologists and general practitioners see NUMELVI’s age range, tablet sizing, and vaccine-positioning as enough to change first-line prescribing. Also worth watching is whether Merck’s convenience messaging translates into smoother acceptance in real-world chronic dermatology cases, where cost discussions, repeat visits, and client follow-through often shape outcomes as much as the drug choice itself. (merck.com)