Lethargy after Afoxolaner (NexGard) in dogs

6,825 reports to the FDA describe lethargy in dogs given Afoxolaner. That is 12% of all reports for this medicine, compared with 11% across reports for all dog medicines.

6,825Reports

48%Marked serious

35%Recovered

7.1%Died or euthanised

1 daysTypical onset

How soon it started

Same day

2,199 38%

1–2 days

1,457 25%

3–7 days

458 7.9%

1–4 weeks

531 9.2%

Over a month

1,123 19%

How the animals did

Recovered

2,406 35%

Recovered with lasting effects

8 0.1%

Still unwell when reported

504 7.4%

Died

250 3.7%

Euthanised

233 3.4%

Not known

3,424 50%

Problems reported at the same time

2,668 39%

2,560 38%

1,549 23%

651 9.5%

583 8.5%

512 7.5%

478 7.0%

476 7.0%

Age of the animals

Under 1 year

1,171

1–3 years

1,712

4–7 years

1,644

8–11 years

1,345

12+ years

582

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 lethargy in dogs?: 6,825 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).

Lethargy with similar medicines

Lethargy after Fluralaner (Bravecto) 6,278 reports · 9.1% of its reports
Lethargy after Sarolaner (Simparica) 1,852 reports · 11% of its reports
Lethargy after Lotilaner (Credelio) 1,033 reports · 10% of its reports
Lethargy after Afoxolaner + Moxidectin + Pyrantel (NexGard PLUS) 747 reports · 8.1% of its reports
Lethargy after Lotilaner + Moxidectin + Praziquantel + Pyrantel (Credelio Quattro) 396 reports · 13% of its reports

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