Blood in stool after Afoxolaner (NexGard) in dogs

110 reports to the FDA describe blood in stool in dogs given Afoxolaner. That is 0.2% of all reports for this medicine, compared with 0.6% across reports for all dog medicines, so it is reported less often than average with this medicine.

110Reports
68%Marked serious
26%Recovered
15%Died or euthanised
2 daysTypical onset
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How soon it started

Same day
34 36%
1–2 days
19 20%
3–7 days
6 6.3%
1–4 weeks
10 11%
Over a month
26 27%

How the animals did

Recovered
29 26%
Still unwell when reported
25 23%
Died
8 7.3%
Euthanised
8 7.3%
Not known
40 36%

Problems reported at the same time

Age of the animals

Under 1 year
12
1–3 years
21
4–7 years
42
8–11 years
19
12+ years
15

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 blood in stool 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 2 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).

Blood in stool with similar medicines

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