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Are Bravecto or Nexgard Safe to Use on Your Dog?

These flea and tick preventives are chewable alternatives to spot-on treatments. But are they safe? Here’s why we’re concerned about them.

Are Bravecto or Nexgard safe?
Nexgard and Bravecto are chewable flea and tick preventives for dogs. Photo: PixelwunderByRebecca

Your head could spin when trying to buy a flea and tick product these days.

It seems like there are a ton of new products out there, but that’s actually not true. The only truly new class of flea and tick preps on the market in the past few years are the isoxazolines.

To put this into brand-name English, we’re talking Nexgard (afoxolaner) and Bravecto (fluralaner), the 2 most commonly prescribed chewable tablets for flea and tick prevention. Simparica (sarolaner) hit the market in March 2016. Another one is Credelio.

What to Know About the “Laners”

  • There are possible neurologic reactions related to these drugs. More on this later.
  • They are highly effective.
  • They are chewable.
  • They are expensive.
  • They are available by prescription only.
  • They last for 3 months (Bravecto) or 1 month (Nexgard).

Until these isoxazolines were discovered, the most effective products in common use were spot-on treatments, like Frontline and Advantix.

But what are the differences? And are these new medications, Bravecto or Nexgard, safe? Let’s get into it.

These flea and tick preventives aren’t exactly new. Photo: akpool1021

Are Bravecto or Nexgard Safe?

Bravecto came onto the market in 2014.

Once a new kind of flea/tick or heartworm medication is developed, every veterinary pharmaceutical company tries to get on board as soon as they can and get their own product out on the market to make as much of a financial killing as possible before their patent runs out.

That’s why products like Advantage used to be by prescription only. Now you can find it anywhere.

Here’s what seems relevant right now:

  • The U.S. Food and Drug Administration (FDA) posted a new warning on Sept. 20, 2018, about possible neurologic reactions related to these drugs. The potential reactions include muscle tremors, ataxia (lack of balance) and seizures: “Be aware of the potential for neurologic adverse events in dogs and cats when treated with drugs that are in the isoxazoline class,” the warning stated in part.
  • More reactions have been reported: “The FDA is working with manufacturers of isoxazaline products to include new label information to highlight neurologic events because these events were seen consistently across the isoxazoline class of products.”

These products work by inhibiting the nervous system of insects. They are not supposed to affect the nervous system of mammals.

Although any drug or anti-parasitic medication can cause side effects, animal poison control, independent science journals and studies had previously found no evidence that these isoxazolines carried serious adverse side effects.

The most common side effects reported have been vomiting, lethargy and diarrhea.

Why the FDA’s Warning Is Relevant

  • The FDA does not issue many warnings on veterinary drugs. Any warning means that veterinarians should reconsider the safety of the drug, and prescribing that drug should carry more thinking and discussion with clients.
  • These products still need a prescription from a vet. The onus is on us vets to make sure we have a long-enough discussion with you, the pet lover, about your animal’s medical history and conditions to decide if these products are safe and appropriate to use.
  • These products should not be prescribed to any animal with any neurologic condition.
  • If your pet has ever had a seizure or a neurologic event, you should not use these drugs.
  • If you use any of these products and your pet has any reaction, don’t use them again.

Bravecto or Nexgard Drug Reactions Are Underreported

Some people freak at even a tiny muscle twinge or vomit after they give their pet a drug, but many folks take a drug reaction in stride and don’t call their vet or the drug manufacturer. The reaction goes unreported.

There are many more reactions to these drugs than the FDA knows about.

The number reported, however, was still enough for the agency to issue this additional warning.

Case #1

An anesthesiologist was talking about using Nexgard.

She said, “Oh, it works great, but my dog had a little seizure after I gave it.”

Now, because she’s a human anesthesiologist, the “little seizure” didn’t freak her out. To a pet lover without a medical background and experience observing seizures, however, this episode could have been highly disturbing.

Though this was not good for the dog, this fairly major reaction went unreported.

Case #2

Nexgard was on the market for about a year. It seemed effective and safe. There weren’t a lot of reports about adverse reactions.

My 13-year-old Cocker Spaniel — with a mild epileptic seizure disorder for his entire life (puppy mill rescue) — hated topical stuff put on him. I used Nexgard without any problem.

Heeding these warnings now, however, I would never have given him Nexgard. He was lucky that I, his loving human and veterinarian, did not make his seizure disorder worse by giving him this drug.

If you notice any reaction in your pet after giving them these medications, tell your vet right away. Photo: ivaylost

Vigilance Is Key

Every individual must ultimately be the judge of whether or not they want to use any product that is highly effective against fleas and ticks on their dog, or run the risk of having their dog get flea-infested or be struck with a tick-borne disease.

Although fleas are an incredible pain in the neck, ticks are more ominous in that they can cause diseases such as Lyme or anaplasmosis.

I stayed away from recommending Bravecto, Nexgard, Credelio or Simparica when they first hit the market. Frontline and Advantix were tried-and-true alternatives, so I prescribed those instead.

These newer medications are considered safe and very effective for the general pet population.

But in the future, before I prescribe them, we’ll have an in-depth discussion about the pet’s health status, any neurologic episodes or conditions that might have gone undocumented, and a careful discussion about the pros and cons of these products.

Be forewarned, though — in a few years, if these drugs are sold over the counter, you won’t have the benefit of talking to anyone but a pet store or Target employee.

Most people don’t like the idea of a topical chemical preventive on their pet. Photo: petraboekhoff


Independent studies conclude that Bravecto, Nexgard, Credelio and Simparica are highly effective in killing fleas and ticks. One drawback, though, is that these oral meds do not repel flea and ticks like some of the spot-ons do.

There may be a slight chance of a tick biting and spreading a disease to your pet before the tick dies.

There are anecdotal reports and many reports from my clients that some resistance is developing to the spot-ons. Since Bravecto and Nexgard are a new class of drugs, there seems to be no or very little resistance.


The new meds cost a few more dollars a month, on average.

The sticker shock with Bravecto is the whopping cost of a single pill, which is around $50 each. That pill covers you for 3 months, however.

The company encourages a “pay as you go” policy, where it will remind and bill you for 1 pill quarterly, splitting up the cost of 4 pills over a year.

Switching From Advantix to Bravecto or Nexgard

Most of my clients switch to an oral med because they don’t like the idea of a chemical sitting on top of their dog’s skin.

Some dogs hate the sensation of the topical and, rarely, the medication causes skin eruptions.

But most people don’t want the spot-on chemical rubbing off on themselves, their children, other pets or their home surfaces. They feel giving the dog a pill means less human and environmental exposure.

Watch this review of other vet-recommended flea and tick preventives:

YouTube player

Bravecto or Nexgard: By Prescription Only

These drugs will be available only by prescription for several years.

You can buy them from your vet or from an internet pharmacy. If you don’t have any relationship with a vet, it could be difficult to get a scrip.

To sum things up, the majority of veterinarians prescribing these products are reporting their clients are happy. People love not putting a substance directly on their dog.

Few of my patients have vomited on the medication, but one dog was sick for several days. More clients had complaints about the spot-ons causing some discomfort and agitation upon application.

Have a careful discussion with your vet about the pros and cons of these products.

vet-cross60pThis pet health content was written by a veterinarian, Dr. Debora Lichtenberg, VMD. It was last reviewed Dec. 16, 2018.

If you have questions or concerns, call your vet, who is best equipped to ensure the health and well-being of your pet. This article is for informational purposes only and is not a substitute for professional medical advice, diagnosis or treatment. See additional information.