I personally do not use any flea and tick prevention chemicals on my pets. I think there are enough toxins in this world that contribute to chronic disease in our pets, without intentionally adding to the problem. After reading about some of these chemicals, you may decide to avoid them, as well. For natural alternatives for flea and tick prevention, read here.

While controlled studies on the new class of chemical oral insecticides being prescribed for flea and tick infestation in dogs have shown an “acceptable” level of side effects, the actual number of anecdotal reports of adverse reactions and death have been staggering. Facebook pages like “Does Bravecto Kill Dogs?”, “Is Bravecto Safe?”, “Bravecto Side Effects Reported”, “BRAVECTO ZKUŠENOSTI”, ” IST BRAVECTO SICHER”, “IS BRAVECTO VEILIG”, and “Does Nexgard Kill Dogs?” bring attention to the number of animals that have had suspected reactions to the drugs. As of February 2016, there were over 5,000 reports of possible adverse reactions to Bravecto and over 2,000 Nexgard reports. I’m sure the numbers have grown since then. The drug manufacturers have made threatening overtones regarding the negative press on social media regarding their products, so any suspected side effects or reactions must be stated as just that – suspect. By making blanket statements like “This drug killed my dog”, the manufacturers have every right to be concerned and we can’t blame them for trying to stop slander without proof. I do urge anyone who uses ANY chemical on their pet to report ANY suspect reactions. The drug manufacturers do provide a list of possible side effects which include:

Toxic Symptoms, Side Effects, Adverse Drug Reactions (ADRs) caused by Fluralaner (Bravecto)

The most frequent ADRs to be expected are:

Vomiting (~7%), Decreased appetite (~6.7%), Diarrhea (~5%), Lethargy (~5.5%), Excessive thirst (polydipsia) (~2%), Excessive gas in stomach or intestine (flatulence) (~1%)

One adult treated dog suffered a seizure during the course of the study (46 days after the second treatment). Abnormal salivation was observed on 17 occasions: in six treated dogs (11 occasions) after dosing and four control dogs (6 occasions). The following abnormalities were noted in 7 pups from 2 of the 10 dams in only the treated group during gross necropsy examination: limb deformity (4 pups), enlarged heart (2 pups), enlarged spleen (3 pups), and cleft palate (2 pups).

Toxic Symptoms, Side Effects, Adverse Drug Reactions (ADRs) caused by Afoxolaner (Nexgard)

Vomiting (~4%), Dry skin (~3%), Diarrhea (~3%), Lethargy (~1.7%), Eating disorders (anorexia) (~1.2%)

Toxic Symptoms, Side Effects, Adverse Drug Reactions (ADRs) caused by Sarolaner

Vomiting (~5.5%), Diarrhea (~1.2%), Lethargy (~1.2%), Inappetence (~1.8%)

From the product insert:

Possible adverse reactions can include abnormal neurologic signs such as tremors, decreased conscious proprioception, ataxia, decreased or absent menace, seizures.

This particular mention on the insert is really alarming and makes me wonder if this could be happening in some of the cases of reported deaths:

“In a separate exploratory pharmacokinetic study, one female dog dosed at 12 mg/kg (3X the maximum recommended dose) exhibited lethargy, anorexia, and multiple neurological signs including ataxia, tremors, disorientation, hypersalivation, diminished proprioception, and absent menace, approximately 2 days after a third monthly dose. The dog was not treated, and was ultimately euthanized. The first two doses resulted in plasma concentrations that were consistent with those of the other dogs in the treatment group. Starting at 7 hours after the third dose, there was a rapid 2.5 fold increase in plasma concentrations within 41 hours, resulting in a Cmax more than 7-fold higher than the mean Cmax at the maximum recommended use dose. No cause for the sudden increase in sarolaner plasma concentrations was identified.”

I would recommend that anyone who suspects their pet has reacted to one of these medications should contact their veterinarian, report the suspected problem to the drug manufacturer, report the suspected problem to the FDA, and ask the treating veterinarian to draw a blood sample that can be tested for drug concentration in the blood. If we had more data, we might have more answers!

Antidote and Treatment of Intoxication:

There is no antidote for isoxazoline derivative (these three drugs) poisoning.

Treatment consists in preventing further exposure together with supportive and symptomatic measures.

These drugs orally administered to dogs are rapidly absorbed into blood. Bioavailability was higher when drug was administered with food.

Excretion occurs mainly in the form of unchanged parent molecule, primarily in the feces.

Environmental Toxicity:

Little to nothing has been published yet regarding the environmental toxicity of these drugs.

Based on their mode of action it must be assumed that they are highly toxic to both aquatic and terrestrial arthropods (insects, ticks, spiders, crustaceans, etc.).

Due to their recent introduction there is very little knowledge on tolerance in different dog breeds or in young, old or otherwise weak animals.

Detailed information on the toxicity and the fate of the drugs in the dog’s body (absorption, distribution, metabolism, excretion) and in the environment is extremely scarce.

My personal reaction: avoid these drugs and other chemicals for my pets.


(Information obtained from Parasitipedia online, as well as product inserts.)