FDA Approves Merck Animal Health’s NUMELVI For Canine Allergic Dermatitis, Atinvicitinib Becomes First Second-Gen JAK Inhibitor For Itch In Dogs

Merck Animal Health, known as MSD Animal Health outside the U.S. and Canada and a division of Merck & Co., Inc., announced that the U.S. Food and Drug Administration has approved NUMELVI™ (atinvicitinib tablets). The product is the first and only second-generation Janus kinase (JAK) inhibitor indicated for the control of pruritus associated with allergic dermatitis in dogs aged six months and older. NUMELVI is expected to be available in veterinary clinics and hospitals across the United States in spring 2026.

“Merck Animal Health is continuously working to expand its portfolio to include innovative veterinary medicinal products that meet the needs of dogs and their owners,” said Tim Kowalski Distinguished Scientist, Discovery Research, Merck Animal Health. “NUMELVI, a second-generation JAK inhibitor, is the first of its kind to enter the market in veterinary medicine, giving it a unique profile compared with other JAK inhibitors. Second-generation JAK inhibitors are already considered the standard of care in human health, and NUMELVI brings that same advanced approach to veterinary medicine.”

Allergic skin conditions are among the most common issues in canine veterinary practice, accounting for up to 20% of general consultations. As allergic dermatitis progresses, it can significantly affect a dog’s quality of life, causing persistent itching, discomfort, and skin lesions, while also impacting the human-animal bond through disrupted sleep and daily routines.

“Merck Animal Health is proud to introduce NUMELVI, our latest advancement geared at rapidly controlling pruritus associated with allergic dermatitis, a common condition that causes distress for so many pets and pet owners,” said Christine McKinney, DVM, DACVD and Senior Professional Services Veterinarian, Merck Animal Health.

“With more than 70 years of innovation and commitment to animal health, we are confident that NUMELVI will offer veterinary professionals a groundbreaking, first-of-its-kind solution aimed at improving the health and well-being of dogs as young as six months of age to mature dogs – and ultimately providing peace of mind for the people who care for them,” added McKinney. “NUMELVI also offers added convenience for veterinary clinics; most dogs, starting at weights as low as 4.4 pounds, require only one or half of a tablet, and there is no need to adjust vaccination schedules. Plus, NUMELVI comes in easy to dispense bottles and can be stored under standard conditions. Its active ingredient is intrinsically stable providing the longest shelf life among JAK inhibitor tablets in veterinary medicine.”

NUMELVI is designed as a once-daily, first-line oral therapy that provides a significant reduction in itch from the first dose. The treatment demonstrates high selectivity for JAK1, at least 10 times more selective for JAK1 compared to JAK2, JAK3, and TYK2 in in vitro assays, targeting cytokines involved in itch and inflammation associated with allergic and atopic dermatitis. This selectivity may help preserve beneficial immune functions mediated by other JAK pathways, supporting a favourable safety profile.

Importantly, NUMELVI is the only JAK inhibitor approved for use in dogs as young as six months old. The approval reinforces Merck Animal Health’s long-standing focus on advancing veterinary medicine through innovation in therapeutics, vaccines, and animal health technologies.