The only JAK inhibitor approved in the U.S. for the control of pruritus associated with allergic dermatitis in dogs six months of age and older

Merck Animal Health, known as MSD Animal Health outside of the United States and Canada, a division of Merck & Co., Inc., Rahway, N.J., USA (NYSE: MRK), announced today the U.S. Food and Drug Administration (FDA) approval of NUMELVI™ (atinvicitinib tablets) – the first and only second-generation Janus kinase (JAK) inhibitor indicated for the control of pruritus associated with allergic dermatitis in dogs six months of age and older. The product is expected to be available at veterinary clinics and hospitals nationwide in spring 2026.

“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 – from as young as six months 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, eliminating the need for a protective film coat or specialized packaging and providing the longest shelf life among JAK inhibitor tablets in veterinary medicine.”

Key Information:

• Why NUMELVI is needed: Skin conditions are common in dogs and can account for up to 20% of cases seen in general veterinary practice¹. As allergic dermatitis progresses, quality of life in dogs and the human-animal bond can be significantly impacted due to physical discomfort, emotional distress, and interruptions in sleep and routines due to itchiness and skin lesions².
• How NUMELVI works: NUMELVI is a once-daily, first-line treatment that leads to a significant reduction in itch from the first dose. It is at least 10 times more selective for JAK1 than for JAK2, JAK3 and TYK2 in in vitro assays³ and inhibits the effect of JAK1-dependent cytokines involved in itch and inflammation in allergic dermatitis including atopic dermatitis. High selectivity for JAK1 can minimize interference with the beneficial immune functions of the other JAKs⁴, resulting in a compelling safety profile with proven efficacy. Moreover, NUMELVI (atinvicitinib tablets) is the only JAK inhibitor approved for use in dogs as young as six months of age.

“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.”

For more information about the first and only second-generation JAK inhibitor for the treatment of allergic dermatitis in dogs from six months of age, visit numelvi.com.

References:

1. Hill PB, Lo A, Eden C.A.N., et al. Veterinary Record. 2006;158:533–539.
2. Noli C. Assessing quality of life for pets with dermatologic disease and their owners. Veterinary Clinics of North America: Small Animal Practice. 2019;49:83–93.
3. Merck Animal Health. Data on file. 2026
4. Bonelli M, Kerschbaumer A, et al. Selectivity, efficacy and safety of JAKinibs: new evidence for a still evolving story. Ann Rheum Dis. 2024;83(2):139–160. doi:10.1136/ard-2023-223850.

About Merck Animal Health

Merck Animal Health, a division of Merck & Co., Inc., Rahway, N.J., USA, is a global animal health business committed to The Science of Healthier Animals™. For more than 130 years, we have pioneered groundbreaking science. Today, we are driven by continuous innovation to develop breakthrough medicines, vaccines and technology. Rooted in direct experience on the farm and in the clinic, we work hand in hand with our customers every step of the way. Our singular focus is to empower those who care for animals, helping them manage their vital responsibility with confidence. Because when it comes to animal health, no one sees it like we do. For more information, visit www.merck-animal-health.com and connect with us on LinkedIn, Facebook, X (formerly Twitter) and Instagram.

Forward-Looking Statement of Merck & Co., Inc., Rahway, N.J., USA

This news release of Merck & Co., Inc., Rahway, N.J., USA (the “company”) includes “forward-looking statements” within the meaning of the safe harbor provisions of the U.S. Private Securities Litigation Reform Act of 1995. These statements are based upon the current beliefs and expectations of the company’s management and are subject to significant risks and uncertainties. There can be no guarantees with respect to pipeline candidates that the candidates will receive the necessary regulatory approvals or that they will prove to be commercially successful. If underlying assumptions prove inaccurate or risks or uncertainties materialize, actual results may differ materially from those set forth in the forward-looking statements.

Risks and uncertainties include but are not limited to, general industry conditions and competition; general economic factors, including interest rate and currency exchange rate fluctuations; the impact of pharmaceutical industry regulation and health care legislation in the United States and internationally; global trends toward health care cost containment; technological advances, new products and patents attained by competitors; challenges inherent in new product development, including obtaining regulatory approval; the company’s ability to accurately predict future market conditions; manufacturing difficulties or delays; financial instability of international economies and sovereign risk; dependence on the effectiveness of the company’s patents and other protections for innovative products; and the exposure to litigation, including patent litigation, and/or regulatory actions.

The company undertakes no obligation to publicly update any forward-looking statement, whether as a result of new information, future events or otherwise. Additional factors that could cause results to differ materially from those described in the forward-looking statements can be found in the company’s Annual Report on Form 10-K for the year ended December 31, 2024 and the company’s other filings with the Securities and Exchange Commission (SEC) available at the SEC’s Internet site (www.sec.gov).

FAQ:

• What is NUMELVI (atinvicitinib tablets)?
  • NUMELVI is a second-generation selective JAK1 inhibitor once daily tablet for dogs for control of pruritus associated with allergic dermatitis.
• Who can receive NUMELVI?
  • Dogs six months of age and older and that weigh at least 4.4 lb. (2 kg), as prescribed by a veterinarian.
• What should I do if my dog is itching incessantly?
  • Connect with your veterinarian as they can help diagnose what’s causing your dog to itch and discuss appropriate treatments. For dogs diagnosed with allergic dermatitis, NUMELVI is a treatment option you can discuss with your veterinarian.
• When should I see a vet about my dog’s itching?
  • Schedule a visit with your vet if your dog is experiencing increased itchiness. Your veterinarian will determine what’s causing your dog to itch and if NUMELVI is right for your dog’s treatment.
• How can I receive a prescription of NUMELVI for my dog?
  • If your dog is experiencing itchiness, speak to your veterinarian to find out if NUMELVI is the right treatment option for your dog.
• How does NUMELVI work?
  • NUMELVI is a once-daily, first-line treatment, and is the only second-generation Janus kinase (JAK) inhibitor indicated for the control of pruritus associated with allergic dermatitis in dogs.
• How is NUMELVI administered?
  • A tablet is taken once daily by mouth at or around meal time, as directed by a veterinarian.
• Can my dog take NUMELVI with other medications?
  • Tell your veterinarian about all medicines and supplements your dog takes before receiving a prescription.
• Can cats use NUMELVI (atinvicitinib tablets)?
  • No, NUMELVI is approved for dogs six months of age and older.

IMPORTANT SAFETY INFORMATION: NUMELVI (atinvicitinib tablets) is not for use in dogs less than 6 months of age or those with serious infections. NUMELVI may increase susceptibility to opportunistic infections, including demodicosis and interdigital furunculosis. Consider the risks and benefits of treatment prior to initiating NUMELVI in dogs with a history of recurrent demodicosis. NUMELVI is a JAK inhibitor. New neoplastic conditions (benign and malignant) have been reported in dogs treated with other JAK inhibitors. The effectiveness and safety of NUMELVI have not been evaluated in a field study beyond 28 days. The safe use of NUMELVI has not been evaluated in breeding, pregnant, or lactating dogs, nor in combination with glucocorticoids, cyclosporine, or other systemic immunosuppressive agents. For complete safety information, refer to the product label.

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