Leucocytosis after Afoxolaner (NexGard) in dogs

The FDA has received 417 reports of leucocytosis in dogs after Afoxolaner. That is 0.7% of all reports for this medicine, compared with 1.0% across reports for all dog medicines.

417Reports
72%Marked serious
18%Recovered
22%Died or euthanised
3 daysTypical onset
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How soon it started

Same day
78 23%
1–2 days
86 25%
3–7 days
41 12%
1–4 weeks
54 16%
Over a month
84 24%

How the animals did

Recovered
73 18%
Recovered with lasting effects
1 0.2%
Still unwell when reported
86 21%
Died
39 9.4%
Euthanised
52 12%
Not known
166 40%

Problems reported at the same time

Age of the animals

Under 1 year
81
1–3 years
88
4–7 years
86
8–11 years
110
12+ years
48

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 leucocytosis in dogs?
417 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).

Leucocytosis with similar medicines

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