Behaviour change after Afoxolaner (NexGard) in dogs

The FDA has received 1,819 reports of behaviour change in dogs after Afoxolaner. That is 3.2% of all reports for this medicine, compared with 2.5% across reports for all dog medicines.

1,819Reports

47%Marked serious

31%Recovered

5.9%Died or euthanised

1 daysTypical onset

How soon it started

Same day

554 37%

1–2 days

310 21%

3–7 days

137 9.1%

1–4 weeks

170 11%

Over a month

330 22%

How the animals did

Recovered

568 31%

Recovered with lasting effects

4 0.2%

Still unwell when reported

146 8.0%

Died

35 1.9%

Euthanised

73 4.0%

Not known

993 55%

Problems reported at the same time

512 28%

346 19%

335 18%

330 18%

299 16%

263 14%

205 11%

Restlessness or agitation

201 11%

Age of the animals

Under 1 year

261

1–3 years

482

4–7 years

461

8–11 years

367

12+ years

145

About this medicine

Afoxolaner kills fleas and ticks; given as a monthly chewable.

Products with this ingredient include NexGard. The FDA hides brand names in its public data, so these reports cover every product with the same active ingredients.

In 2018 the FDA alerted owners and vets that isoxazoline products have been associated with neurologic reactions such as muscle tremors, wobbliness (ataxia) and seizures, including in animals with no history of them.

Questions owners ask

Can Afoxolaner cause behaviour change in dogs?: 1,819 reports link the two, but a report alone does not prove the medicine was the cause: other illnesses, other medicines or coincidence can be involved. Your vet can judge it for your animal.
How soon after a dose was it reported?: In half of the reports with dates, it started within 1 day of the first dose.
What should I do?: Don't give another dose until you've spoken to your vet, and keep the packaging so you can tell them the product and dose. Your vet can also report it to the FDA (or you can, through the manufacturer or FDA form 1932a).

Behaviour change with similar medicines

Behaviour change after Fluralaner (Bravecto) 1,712 reports · 2.5% of its reports
Behaviour change after Sarolaner (Simparica) 718 reports · 4.3% of its reports
Behaviour change after Lotilaner (Credelio) 488 reports · 4.9% of its reports
Behaviour change after Afoxolaner + Moxidectin + Pyrantel (NexGard PLUS) 172 reports · 1.9% of its reports
Behaviour change after Lotilaner + Moxidectin + Praziquantel + Pyrantel (Credelio Quattro) 199 reports · 6.5% of its reports

All reported side effects of Afoxolaner in dogs · Medicines most reported with behaviour change