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Amid a myriad of products to control fleas and ticks in pets comes one promising 12-month protection with a single injection. First approved in Australia in 2023, the drug received approval in the United States last month.

The launch in the United States of the first long-acting treatment to prevent fleas and ticks in dogs is stirring a mix of excitement and caution among veterinarians, as they weigh the benefit of uninterrupted 12-month coverage with concerns about neurological side effects that can be caused by the product's active ingredient.

The product's cost compared with shorter-acting treatments also has veterinarians wondering if some pet owners will be uncomfortable paying more up front for extended coverage, particularly for larger dogs that require a greater, and therefore more expensive, dose.

Bravecto Quantum, an injectable product manufactured by pharmaceutical company Merck, is designed to protect dogs from fleas (Ctenocephalides felis) for 12 months from a single dose. It also promises 12-month protection against three types of ticks: the black-legged tick (Ixodes scapularis), the American dog tick (Dermacentor variabilis) and the brown dog tick (Rhipicephalus sanguineus). Protection against a fourth type of tick, the lone star tick (Amblyomma americanum), is said to last eight months.

The product's active ingredient is fluralaner, an insecticide from the isoxazoline class of drugs, which has been found to cause neurological side effects such as seizures in a small proportion of dogs and cats. Fluralaner is the active ingredient in shorter-acting Bravecto products that have been on the market for years, including orally administered chews that last up to three months and a topical (spot-on) treatment that lasts up to six months. Isoxazoline-class drugs are present in other brands of shorter-acting treatments, such as Credelio, NexGard and Simparica.

Bravecto Quantum first debuted in Australia, having received approval from that country's veterinary drugs regulator in 2023. It has since been released in dozens of other countries, including throughout the European Union, where it was approved in 2024.

In the U.S., Bravecto Quantum was approved by the Food and Drug Administration on July 10. "Distribution has begun and will continue to roll out throughout August," Dr. Christine Royal, vice president of Merck Animal Health's companion animal and equine business unit, told the VIN News Service.

According to Royal, the company spent 10 years developing Bravecto Quantum, which releases slowly in the patient's body at a low-dose rate. The recommended dose equates to 15 milligrams of fluralaner per kilogram of body weight, which is substantially lower than Bravecto chews, for instance, which provide a minimum dose of 25 mg/kg.

A key attraction of Bravecto Quantum, she maintains, is that it eliminates the risk of compliance failures by pet owners who forget or choose not to use shorter-acting products regularly.

Veterinarians watchful for side effects

Talk among veterinarians about Bravecto Quantum has been picking up in recent months on message boards of the Veterinary Information Network, an online community for the profession and parent of VIN News. Some practitioners welcome the product's launch enthusiastically, positing that it will fill compliance gaps. Others are hesitant to use it immediately due to concerns about side effects — especially, some say, because the product remains in a patient's body for a year.

In 2018, drugs in the isoxazoline class prompted an alert from the FDA after being associated with neurological problems, including muscle tremors, ataxia (loss of body control) and seizures.

Merck conducted a number of studies to determine the efficacy and safety of Bravecto Quantum that involved hundreds of dogs combined, according to the FDA's Freedom of Information report about the product. A total of four dogs experienced seizures during two of the studies, one of which died.

In a 15-month field trial to assess the product's efficacy and safety for controlling fleas, 225 dogs received Bravecto Quantum once every 12 months, and 114 dogs received it once every six months.  The most commonly reported side effects included lethargy, decreased appetite, vomiting and diarrhea. Three dogs had seizures (two in the once-every-12-months group and one in the once-every-six-months group). Two of the dogs' seizures were managed with anticonvulsant medication, with one of dogs removed from the trial after 84 days. The third dog stopped having seizures without the aid of medication.

In a separate study that solely tested safety and involved 36 beagles, one dog given three times the recommended dose experienced seizures on day 475 and had to be euthanized. The cause of death was determined as polyarteritis, a condition that involves inflammation of the arteries. The death was "possibly drug-related," the study concluded.

"Based on the data submitted by the sponsor for the approval of Bravecto Quantum, FDA determined that the drug is safe and effective when used according to the labeling," the regulatory report concludes.

Bravecto Quantum

VIN News Service photo

A single 20-mL package of Bravecto Quantum comes with two vials: one containing the active ingredient fluralaner and one containing a drug-carrying solution.

Merck's Royal told VIN News that reported adverse events during the company's trials were generally mild and self-limiting. "With that said, veterinarians should carefully consider the timing and likelihood that any observed signs are actually related to the treatment," she said. "Our data — along with over a decade of experience with the 12-week Bravecto chews — show that these signs, when they do occur, are typically short-lived and don't last throughout the entire treatment period."

She added that a dog that has responded well to shorter-acting products won't necessarily have the same experience with Bravecto Quantum. "If a dog has tolerated Bravecto chews well, that's a positive indicator, though not a guarantee of an identical response," Royal said.

In the European Union, adverse reactions to drugs must be recorded on the region's EudraVigilance database, which is accessible to the public. Adverse events data specifically for Bravecto Quantum can't be distinguished on the database, though, because they are combined for all Bravecto products, with the exception of Bravecto Plus, which is categorized separately because it contains moxidectin that protects against heartworms, roundworms and hookworms.

Moreover, directly comparing adverse event reporting rates for Bravecto Quantum versus Bravecto and Bravecto Plus is difficult at this stage, Royal said, because "reporting practices and requirements vary across the globe."

Dr. Tina Wismer, senior director of toxicology for the ASPCA Animal Poison Control Center in the U.S., noted that another product that lasts 12 months, the heartworm drug ProHeart 12, doesn't appear to have caused more adverse events than its shorter-lasting iterations — at least not judging from reports to the center. ProHeart 12 was approved by the FDA in 2019.

Typically, Wismer said, the risk of side effects shouldn't increase due to the delivery method.

Veterinarians from Australia, New Zealand share experiences

In Australia, Bravecto Quantum is proving popular at Dr. Jill King's practice in Pittwater, an affluent suburb on Sydney's northern beaches, where paralysis ticks (Ixodes holocyclus) are prevalent. (Paralysis ticks are covered by the Australian version of the product.)

"If you're not covered for your parasite control in the springtime especially, your dog can easily get tick paralysis and die," King said, adding that many pet owners forget to re-administer shorter-acting products.

"What we found with the one-month and three-month treatments is that owners would arrive, the animal's got signs of tick paralysis, you ask them about what's been given, and they start saying, 'Oh, I'll ring my wife.' Everybody passes the buck on whether the animal's actually covered," she said. "So Quantum is just a game-changer for us. We can say, 'Ah, this dog had Quantum at this time, so it's unlikely to have a paralysis tick.' "

Still, the product's cost could act as a barrier for some pet owners, King said, particularly those with larger dogs. Some practices may employ a flat or relatively flat pricing strategy where the same or similar amount is charged regardless of a dog's size — the smaller dogs essentially subsidizing the larger dogs, King said. Her practice, however, charges based on weight.

For a 5-kg (11-lb) dog, for example, she charges A$143 (US$93) for Bravecto Quantum, which includes an injection fee. For a 35-kg (77-lb) dog, her price is A$519 (US$339).

Merck's Royal said the company has suggested retail prices to veterinarians that reflect "a lower cost compared to 12 months of many other flea and tick products on the market." The company, she added, is offering a reimbursement program to veterinarians for larger-sized dogs.

Dr. Jessica Kenworthy, a veterinarian in the southern outskirts of Melbourne, Australia, also is seeing robust demand for Bravecto Quantum, notwithstanding a few clients put off by its price.

"There have been a couple of occasions where there's been a bit of pushback, especially once you start getting into dogs that are 30-kg-plus," she said, "because I think the price might be around $400 (US$261) at that point."

Assessing a client's lifestyle could help veterinarians determine if Bravecto Quantum is right for them, she added. "If they have a really busy schedule, they're not going to be on top of remembering to give that shorter-lasting protection, we will be 'OK, this definitely is a good option for you guys,' " she said. "Obviously, it depends on risks as well — if they're in a tick risk area or if they do a lot of travel."

The cost of not covering an animal consistently could be considerably higher than paying for Bravecto Quantum, according to King, who notes that treating tick paralysis costs around A$1,500 (US$978).

Practices aren't equally keen on the product. For example, a veterinarian in Otago, New Zealand, posted recently to a VIN message board: "Our clinic opted to not stock it as each of us vets decided we wouldn't use it in our own dogs."

The veterinarian said her own dog had seizures with the Bravecto spot-on product. That made her nervous about Bravecto Quantum, since it stays in a patient's body longer.

The veterinarian, who asked not to be named for personal privacy reasons, added, "We did think there may be a good market for it in working dogs, where remembering to apply a product to multiple dogs may be difficult."

For her part, King in Australia wonders if the slow-release nature of Bravecto Quantum could actually make it safer than shorter-acting treatments because they aren't getting a big hit of the drug all at once.

Recently, King said, she was concerned about a dog that had seizures after consuming Bravecto chews. The dog had suffered seizures before, so it was unclear if the chews were responsible. King decided to give the dog lower-dosed chews made for puppies. "And then we bravely gave her a Bravecto Quantum injection without any trouble at all."

King said she hasn't seen any notable adverse reactions to Bravecto Quantum to date, apart from a dog that experienced swelling at the injection site.

Kenworthy, too, said her patients have tolerated Bravecto Quantum well. "We did about 52 injections in the fist six month of this year, so about nine a month," she said. "So far, we haven't had any reported neurological side effects, we haven't had any reported injection reactions or any reported hypersensitivity reactions like anaphylaxis."