Increased percentage reticulocytes after Afoxolaner (NexGard) in dogs

The FDA has received 86 reports of increased percentage reticulocytes in dogs after Afoxolaner. That is 0.2% of all reports for this medicine, compared with 0.1% across reports for all dog medicines.

86Reports
62%Marked serious
16%Recovered
29%Died or euthanised
5 daysTypical onset
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How soon it started

Same day
18 26%
1–2 days
14 20%
3–7 days
6 8.7%
1–4 weeks
11 16%
Over a month
20 29%

How the animals did

Recovered
14 16%
Still unwell when reported
15 17%
Died
11 13%
Euthanised
14 16%
Not known
32 37%

Problems reported at the same time

Age of the animals

Under 1 year
10
1–3 years
22
4–7 years
26
8–11 years
19
12+ years
9

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 increased percentage reticulocytes in dogs?
86 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 5 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).

Increased percentage reticulocytes with similar medicines

All reported side effects of Afoxolaner in dogs · Medicines most reported with increased percentage reticulocytes