Lymphopenia after Fenbendazole in dogs

The FDA has received 33 reports of lymphopenia in dogs after Fenbendazole. That is 0.6% of all reports for this medicine, compared with 0.3% across reports for all dog medicines, so it is reported unusually often with this medicine.

33Reports

94%Marked serious

27%Recovered

24%Died or euthanised

12 daysTypical onset

How soon it started

Same day

4 14%

1–2 days

2 7.1%

3–7 days

4 14%

1–4 weeks

13 46%

Over a month

5 18%

How the animals did

Recovered

8 24%

Recovered with lasting effects

1 3.0%

Still unwell when reported

10 30%

Died

2 6.1%

Euthanised

6 18%

Not known

6 18%

Problems reported at the same time

21 64%

20 61%

17 52%

16 48%

16 48%

15 45%

12 36%

11 33%

Age of the animals

Under 1 year

1–3 years

4–7 years

8–11 years

12+ years

About this medicine

Fenbendazole treats intestinal worms and some other parasites.

Questions owners ask

Can Fenbendazole cause lymphopenia in dogs?: 33 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 12 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).

Lymphopenia with similar medicines

Lymphopenia after Pyrantel + Sarolaner (Simparica Trio) 41 reports · 0.1% of its reports

All reported side effects of Fenbendazole in dogs · Medicines most reported with lymphopenia