Numelvi, the New Once-Daily Itch Pill for Dogs: What the Trial Showed

On February 25, 2026, the FDA approved Numelvi (atinvicitinib), a once-daily prescription tablet that controls itching from allergic dermatitis in dogs 6 months and older. It belongs to the same drug family as the familiar itch pill oclacitinib (Apoquel), but targets one immune signal more selectively. Its main trial showed a real, modest benefit, and its long-term safety record is still short. Here’s what that means if your vet brings it up.

What “second-generation JAK inhibitor” means

JAK inhibitors block enzymes called Janus kinases, which carry itch and inflammation signals inside cells. There are four: JAK1, JAK2, JAK3 and TYK2. Numelvi is designed to hit JAK1 much more than the others; Merck, its maker, says it’s “at least 10 times more selective for JAK1 than for JAK2, JAK3 and TYK2” in lab tests, and calls it the first “second-generation” JAK inhibitor for this use.

Two things to keep in mind. “Second-generation” is the company’s description, and the 10-times figure comes from test-tube assays, not dogs. And no study has compared Numelvi with Apoquel head to head, so there’s no evidence yet that one controls itch better or is safer than the other. What the FDA’s own summary does say: it isn’t a steroid or an antihistamine, and the FDA classifies it as an immunosuppressant.

What the trial showed

The pivotal study was masked, randomized and placebo-controlled, at 26 U.S. clinics between 2022 and 2024. Of 289 dogs enrolled, 250 were analyzed, aged from about 8 months to 15 years. Owners scored their dog’s itch on a 0-to-10 scale every day.

• The strict test: success meant itch cut at least in half on at least 5 of the first 7 days. 23% of Numelvi dogs met it, against 7% on placebo.
• The average picture: itch scores fell from 7.4 to 3.3 by day 7 on Numelvi, and from 7.6 to 5.4 on placebo. The Numelvi group was lower at every time point after the start (day 0).

In other words, the treated group became clearly less itchy on average, but only about one dog in four met the demanding definition of success within the first week.

Safety

In the 28-day field trial, compared with placebo:

	Numelvi	Placebo
Vomiting or nausea	6.9%	4.2%
Ear infection (otitis)	6.3%	5.6%
Diarrhea	4.2%	10.4%

Bloodwork changes linked to the drug included lower white blood cell counts, higher liver and kidney values and higher cholesterol, which is why your vet will want to check blood on long-term use.

In a six-month laboratory study at one, three and five times the maximum dose, one dog at five times the dose developed widespread mange (demodicosis), which the FDA attributed to the drug suppressing its immune system; that dog was euthanized. Infections of the skin between the toes (interdigital furunculosis) were seen at the higher doses. The good news from the same work: puppies given three times the maximum dose for 84 days still mounted adequate immune responses to distemper, adenovirus, parvovirus and rabies vaccines.

From the label, as Merck summarizes it: not for dogs under 6 months or with serious infections; it may make infections, including mange, more likely; other JAK inhibitors have been linked to new tumors; and it hasn’t been tested in breeding, pregnant or nursing dogs, or together with steroids or cyclosporine. The FDA’s summary is blunt about the main gap: “Current field safety data is limited to 28 days,” while allergic dogs often need treatment for years.

Why the age matters

One practical difference is age. Numelvi is labeled from 6 months; the UK label for Apoquel says not to use it in dogs under 12 months. If you have an itchy young dog between those ages, that’s a question worth asking your vet.

How it’s given

Once a day, with food. It matters: the peak blood level was 280% higher when the tablet was given with a meal than on an empty stomach. Wash your hands after handling the tablets.

The bigger picture

An itch pill controls the itch; it doesn’t tell you what your dog is allergic to. If you’re still sorting out whether it’s food or the environment, my guide to food versus environmental allergies explains how vets tell them apart, the free allergy and food diary gives you the record your vet will ask for, and a medication log helps if your dog ends up on a daily pill. Numelvi was also approved in the European Union in July 2025.