FDA clears NUMELVI for allergic itch control in dogs: full analysis

The FDA has approved NUMELVI (atinvicitinib tablets), a new once-daily oral therapy from Merck Animal Health for the control of pruritus associated with allergic dermatitis in dogs 6 months of age and older. Approved on February 25, 2026, the product is being positioned as the first and only second-generation JAK inhibitor cleared in the U.S. veterinary market for this use, giving clinicians a new entrant in one of companion animal medicine’s busiest therapeutic categories. (animaldrugsatfda.fda.gov)

The approval lands in a dermatology market where demand for fast, practical itch control remains high. Allergic dermatitis and atopic dermatitis are among the most common reasons dogs present in general practice, and manufacturers have increasingly framed itch control not just as a medical issue, but as a quality-of-life issue for both the patient and the pet parent. Merck had already been building toward broader commercialization: NUMELVI received a positive opinion from the European Medicines Agency’s Committee for Veterinary Medicinal Products in June 2025, followed by European Commission approval in July 2025. (merck-animal-health.com)

The FDA’s Freedom of Information summary adds useful detail beyond the initial announcement. The drug is approved at 0.8 to 1.2 mg/kg orally once daily with food. In the pivotal field study, conducted from February 2022 to July 2024, 289 client-owned dogs with allergic dermatitis were enrolled across multiple U.S. sites. FDA reviewers said the study demonstrated effectiveness for controlling pruritus for up to 28 days. The same summary notes that the selected once-daily regimen produced better control of pruritus and skin lesions than a lower twice-daily regimen evaluated earlier in development. (animaldrugsatfda.fda.gov)

Merck has also pointed to additional clinical data presented at the 2025 European Veterinary Dermatology Congress. In that company-reported presentation, 87.5% of dogs receiving the recommended once-daily dose achieved at least a 50% reduction in itching or skin lesion severity index, compared with 23.1% in the placebo group. Because those data come from a company news release rather than a peer-reviewed publication, they’re best viewed as supportive context rather than the final word, but they help explain Merck’s messaging around rapid and clinically meaningful itch relief. (merck-animal-health.com)

Industry reaction has focused on differentiation within the JAK class. Merck and trade coverage have stressed that atinvicitinib is more selective for JAK1 than for JAK2, JAK3, and TYK2, and have framed that selectivity as potentially reducing interference with other immune pathways. That said, the practical takeaway for clinicians will still come down to labeled use, real-world tolerability, cost, and how the product performs in comparison with established options already embedded in hospital protocols. dvm360 also highlighted a clinic-operations angle, noting Merck’s claim that many dogs will need only one or half a tablet and that the product can be stored under standard conditions. (merck-animal-health-usa.com)

Why it matters: For veterinary teams, NUMELVI expands the menu of oral antipruritic choices at a time when dermatology caseloads remain consistently high in general practice. The label matters here: this approval is for control of pruritus associated with allergic dermatitis, not a blanket claim across every allergic skin presentation. Safety language also deserves close reading. The product label says NUMELVI should not be used in dogs under 6 months of age or in dogs with serious infections, and the most commonly reported adverse reactions through day 28 included vomiting or nausea, otitis externa, hematuria, anorexia, bacterial skin infection, diarrhea, crystalluria, lethargy, and urinary tract infection. For practices, that means case selection, recheck planning, and pet parent counseling will remain central, especially when dogs have concurrent disease or a history of recurrent infection. (merck-animal-health-usa.com)

The approval may also have competitive implications. Merck is explicitly marketing NUMELVI as a first-line option and as a next-generation JAK product, borrowing language that has already been used in human medicine. Whether that translates into meaningful market share will depend on pricing, availability, formulary decisions, and whether dermatologists and general practitioners see clear advantages in day-to-day use. The company has said the product is expected to become available in U.S. veterinary clinics in spring 2026, so uptake data may emerge quickly once distribution begins. (merck.com)

What to watch: Near term, watch for clinic launch timing this spring, any peer-reviewed publication of the pivotal or congress-presented data, and early feedback from dermatologists and general practitioners on where NUMELVI fits relative to existing itch-control standards. (merck.com)