Didn't work as expected after Afoxolaner (NexGard) in dogs

The FDA has received 8,625 reports of didn't work as expected in dogs after Afoxolaner. That is 15% of all reports for this medicine, compared with 13% across reports for all dog medicines.

8,625Reports

13%Marked serious

2.5%Recovered

0.8%Died or euthanised

128 daysTypical onset

How soon it started

Same day

399 10%

1–2 days

131 3.4%

3–7 days

156 4.1%

1–4 weeks

612 16%

Over a month

2,512 66%

How the animals did

Recovered

197 2.3%

Recovered with lasting effects

21 0.2%

Still unwell when reported

1,984 23%

Died

26 0.3%

Euthanised

41 0.5%

Not known

6,356 74%

Problems reported at the same time

4,644 54%

887 10%

391 4.5%

168 1.9%

111 1.3%

88 1.0%

88 1.0%

83 1.0%

Age of the animals

Under 1 year

608

1–3 years

3,028

4–7 years

2,230

8–11 years

1,229

12+ years

371

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 didn't work as expected in dogs?: 8,625 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 128 days 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).

Didn't work as expected with similar medicines

Didn't work as expected after Fluralaner (Bravecto) 5,946 reports · 8.6% of its reports
Didn't work as expected after Sarolaner (Simparica) 1,487 reports · 8.9% of its reports
Didn't work as expected after Lotilaner (Credelio) 1,497 reports · 15% of its reports
Didn't work as expected after Afoxolaner + Moxidectin + Pyrantel (NexGard PLUS) 1,527 reports · 16% of its reports
Didn't work as expected after Lotilaner + Moxidectin + Praziquantel + Pyrantel (Credelio Quattro) 292 reports · 9.5% of its reports

All reported side effects of Afoxolaner in dogs · Medicines most reported with didn't work as expected