Capstar for Screwworm in Dogs: FDA's New EUA Explained

You're packing the trunk for an autumn drive through South Texas or perhaps the rescue pup that rode from Mexico has joined your family. Then your title catches you: a parasite that feeds on living tissue with its maggots is in the news again and your flea pill in your cabinet has a new job! You will find out in the coming few minutes exactly what the FDA authorized, who the people who should care are and what you should do next.

Quick answer: FDA granted the Capstar/EUA on September 3, 2026. They are the first federally permitted options to prevent the New World screwworm fly infestation rather than just to treat it once it has occurred. The tablets are available for over-the-counter sale for pets 4 weeks or older that weigh 2 pounds or more. But, for most pets in the U.S., the risk is still low and it is important to remember if your dog lives in, travels to, or has come from an affected area. (Source: FDA)

Nitenpyram for Dogs: What the FDA Authorization Actually Covers

Capstar is a well-known brand in the pet shops. A lot of families already have one of these boxes of over-the-counter pills readily available for fleas.

That tablet got its new assignment on September 3, 2026, from the FDA. It issued an Emergency Use Authorization (EUA) for Capstar, and an amendment of that EUA for the generic version. Both are now approved for prevention and treatment of infestations from the larvae of New World screwworms (Source: FDA). In June 2026, the generic tablets had been approved for only treatment (Source: FDA).

That's important for the following reason. Until now, all approved or approved with conditions alternatives have only addressed an existing infestation in dogs and cats. The move was a response to a "previously unmet need," FDA veterinary chief Timothy Schell said. (Source: FDA)

Why an Emergency Use Authorization Isn't Full Approval

An EUA is a quicker and short-term path. The FDA concluded it is reasonable to believe these tablets may be effective for this use, and that the known benefits outweigh the known risks (Source: FDA). That is an evidence bar lower than typical drug approval.

The authorization stays in effect until it is revoked or until the HHS Secretary ends the emergency declaration behind it (Source: FDA). This plainly is a hopeful instrument, not a guarantee. It also isn't a substitute for your veterinarian's judgment.

Does My Dog Need Screwworm Medication? Who's Actually at Risk

The truth for most American dogs is no – not at this time. According to the FDA, most dogs and cats in the U.S. are at low risk because the number of cases is small and only limited to a small geographic region (Source: FDA). The parasite was eradicated in the U.S. decades ago with the help of a sterile-fly program, (Source: USDA APHIS).

According to the FDA, these pets are pets that should be watched more closely:

• Dogs residing in areas where the state or federal officials have determined infestations exist
• Dogs going to and from these areas
• Pets from the following countries south of the U.S. border or pets that reside in such countries

Consider it a continuum. If a dog never leaves the Chicago apartment building, this news is background. But a rescue dog from an impacted area, or a hunting dog returning from such an area, is another matter.

Numbers change rapidly and should not be taken as definitive, even if stated in an article such as this. USDA maintains a public dashboard of detections made in the U.S. (Source: USDA APHIS). When taking pets on the road this fall, take a check before you leave and a check on your return.

Looking for an adoption from an impacted area? For new pet owners, make sure to schedule a veterinarian appointment to your first week's to-do list. Your vet will be familiar with the local circumstances and able to advise you as to whether a preventative tablet is worthwhile.

New World Screwworm Symptoms in Dogs: What to Watch For

The best way to detect problems is to be familiar with the parasite's operations. A female fly deposits eggs in the open wounds or close to the body openings. The maggots (larvae) then enter into healthy flesh rather than feeding only on dead flesh (Source: USDA APHIS). Infestations, if left untreated, can lead to serious damage and even death (USDA APHIS).

The FDA lists these warning signs for owners:

• Maggots seen in a wound or opening of the body
• A bad smell from a wound or body opening
• Trouble spots near the eyes, ears, nose and mouth

Veterinarians also identify when a wound is not healing, as well as signs of pain or agitation and loss of appetite (Source: veterinary guidance). None of these symptoms is conclusive of the presence of the parasite, but all of these symptoms warrant a call to your veterinarian.

Where the Fly Gets In

The parasite requires a wound in the skin. Some common entry points that a dog can use are:

• Scrapes and scratches from brush, fences or rough play
• Bite wounds from fighting:
• Spots where a tick was removed
• Fresh surgical incisions

When to Skip the Tablet and Call the Vet

Tablet is a prevention device. If a dog is actively infested, it's a veterinary emergency and as per the FDA's guidance, you should seek veterinary advice for infested pets quickly (Source: FDA). Cleaning wounds and examining the tissues is not a task for a kitchen counter.

What Does a Screwworm Wound Look Like? A Visual Checklist

Imagine a wound that doesn't seem like it should look. Not shrinking, it's expanding — and growing more radical, more militant, more aggressive — by the day. Here are some fast guidelines to go over:

1. Is it healing? Healthy wounds heal, shrink and dry up. If the wound is getting larger, or if the wound is weeping or appears to be deeper every day, it's a red flag.
2. Is there movement or larvae observed? Pay close attention to the wound and wound area for little, pale, worm-like maggots.
3. Does it smell? One of the FDA named warning signs is a strong, foul smell emanating from a wound or body opening (Source: FDA).
4. Is your dog reacting? Signs of pain include licking, whining, hiding, flinching, or not eating.
5. Have you checked the openings? Check eyes, ears, nose, and mouth, NOT just the legs and belly.

Here is a crucial warning; a number of types of fly larvae may attack wounds and only a vet can diagnose the type of problem. Take a good picture of anything that matches this checklist. Do not allow the dog to lick or scratch the area and contact your veterinarian or emergency facility immediately.

Looking for more of a daily routine that you can follow? Check out our wound-check guide for a head to tail check that can be completed in less than five minutes. It's a natural thing to do during bath time so incorporate it into your grooming routine.

How to Prevent Screwworm in Dogs: A Practical Plan

Tablet is one level of security. The following is how to lay the layers.

Step 1: Size up your Real Risk

Ask three questions. Is my dog in an affected area? Do we have a journey to one? Was my dog just from one? If the answer to all three is no, there is low risk, which is the FDA's own take for the majority of U.S. pets (Source: FDA).

Step 2: Talk to your Vet before you give a Tablet

There's a lot that can be covered in a quick call. Inquire about your dog's weight, any medical issues, and other medication or flea products that are used. According to FDA, the dose depends on your pet's weight, so be sure to have your veterinarian verify the appropriate size.

Step 3: Ignore the fact that they have been told in the flea box, and take instruction from the Fact Sheet

This is an error to avoid. It's easy to dose Capstar by heart since it's a familiar name. However, emergency use comes with its own fact sheet and instructions and the FDA advises owners to read the fact sheet before using (Source: FDA). The agency also recommends that these tablets should not be given to pets less than 2 lbs or younger than 4 weeks old (Source: FDA).

Step 4: Wound Checks – Make it a habit!

So, everyday wound care is your first line of defense against the parasite, since it enters through broken skin. After outdoor play and every day while traveling check your dog. Wounds are to be kept clean, small wounds to be treated quickly, and do not think that a tablet will take the place of this.

Last Step: Review the Rules every few weeks

EUAs are subject to revisions. The generic version's authorization was updated just months after its first one (Source: FDA). Make it a habit to bookmark FDA's official fact sheet page and check it before travelling anywhere.

Capstar vs. Other Authorized Options: Prevention vs. Treatment

Capstar is not the only product to have an emergency authorization. So far, it is the only one to include prevention. These are the FDA approved choices compared:

The FDA's first-ever EUAs for an animal drug were for Credelio (Source: FDA). More products may be available, consult your veterinarian about which is right for your pet.

The Bottom Line:

Not only is it a treatment, but FDA's September 3 authorization offers pet owners in the United States a new option: prevention. Most dogs are not at high risk, this is really for pets in affected areas. Keep a sense of calm, discuss with your vet and follow official fact sheet, and check wounds every day. Looking to brush up on that last one? Take a look at our wound-check guide, next, to see what to look for.

This article is educational and isn't a substitute for veterinary advice. Please read our disclaimer.

References:

• U.S. Food and Drug Administration, "FDA Issues Emergency Use Authorization for Drugs to Prevent and Treat New World Screwworm in Dogs and Cats," Sept. 3, 2026.
• U.S. Food and Drug Administration, Letter of Authorization to Sergeant's Pet Care Products LLC (Capstar EUA), Sept. 3, 2026.
• U.S. Food and Drug Administration, "FDA Issues Emergency Use Authorization for New World Screwworm Drug for Dogs" (Credelio).
• U.S. Food and Drug Administration, CVM Update: "FDA Issues Emergency Use Authorizations for Drugs to Treat New World Screwworm in Dogs and Cats" (NexGard, NexGard COMBO).
• USDA APHIS, "Confirmed Detections of New World Screwworm" dashboard.
• USDA APHIS, screwworm program information page.
• Medical Daily, "Pet Owners Can Now Prevent Screwworm Infestations in Dogs and Cats Under a New Federal Authorization," Sept. 4, 2026 (secondary reporting on wound entry points and warning signs).