Didn't prevent heartworm after Afoxolaner (NexGard) in dogs

831 reports to the FDA describe didn't prevent heartworm in dogs given Afoxolaner. That is 1.5% of all reports for this medicine, compared with 13% across reports for all dog medicines, so it is reported less often than average with this medicine.

831Reports

7.9%Marked serious

5.5%Recovered

0.8%Died or euthanised

294 daysTypical onset

How soon it started

Same day

2 1.0%

1–2 days

2 1.0%

3–7 days

0 0.0%

1–4 weeks

10 4.9%

Over a month

190 93%

How the animals did

Recovered

11 1.3%

Recovered with lasting effects

35 4.2%

Still unwell when reported

149 18%

Died

4 0.5%

Euthanised

3 0.4%

Not known

629 76%

Problems reported at the same time

Didn't work as expected

39 4.7%

33 4.0%

23 2.8%

20 2.4%

19 2.3%

17 2.0%

13 1.6%

13 1.6%

Age of the animals

Under 1 year

1–3 years

515

4–7 years

209

8–11 years

12+ years

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 prevent heartworm in dogs?: 831 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 294 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 prevent heartworm with similar medicines

Didn't prevent heartworm after Fluralaner (Bravecto) 638 reports · 0.9% of its reports
Didn't prevent heartworm after Sarolaner (Simparica) 287 reports · 1.7% of its reports
Didn't prevent heartworm after Lotilaner (Credelio) 487 reports · 4.9% of its reports
Didn't prevent heartworm after Afoxolaner + Moxidectin + Pyrantel (NexGard PLUS) 1,168 reports · 13% of its reports
Didn't prevent heartworm after Lotilaner + Moxidectin + Praziquantel + Pyrantel (Credelio Quattro) 126 reports · 4.1% of its reports

All reported side effects of Afoxolaner in dogs · Medicines most reported with didn't prevent heartworm