Lymphocytosis after Afoxolaner (NexGard) in dogs

110 reports to the FDA describe lymphocytosis in dogs given Afoxolaner. That is 0.2% of all reports for this medicine, compared with 0.1% across reports for all dog medicines, so it is reported unusually often with this medicine.

110Reports
60%Marked serious
16%Recovered
15%Died or euthanised
3 daysTypical onset
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How soon it started

Same day
19 21%
1–2 days
21 23%
3–7 days
13 14%
1–4 weeks
13 14%
Over a month
24 27%

How the animals did

Recovered
18 16%
Still unwell when reported
17 15%
Died
7 6.4%
Euthanised
9 8.2%
Not known
59 54%

Problems reported at the same time

Age of the animals

Under 1 year
48
1–3 years
26
4–7 years
17
8–11 years
15
12+ years
3

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 lymphocytosis in dogs?
110 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 3 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).

Lymphocytosis with similar medicines

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