Underdose after Fenbendazole in dogs

The FDA has received 229 reports of underdose in dogs after Fenbendazole. That is 3.9% of all reports for this medicine, compared with 1.0% across reports for all dog medicines, so it is reported unusually often with this medicine.

229Reports

35%Marked serious

37%Recovered

4.8%Died or euthanised

1 daysTypical onset

How soon it started

Same day

43 42%

1–2 days

33 32%

3–7 days

4 3.9%

1–4 weeks

14 14%

Over a month

8 7.8%

How the animals did

Recovered

85 37%

Still unwell when reported

76 33%

Died

10 4.4%

Euthanised

1 0.4%

Not known

57 25%

Problems reported at the same time

110 48%

43 19%

43 19%

42 18%

33 14%

16 7.0%

Didn't work as expected

13 5.7%

Incorrect dose administered

12 5.2%

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 underdose in dogs?: 229 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 1 day 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).

Underdose with similar medicines

Underdose after Pyrantel + Sarolaner (Simparica Trio) 216 reports · 0.4% of its reports
Underdose after Febantel + Praziquantel + Pyrantel (Drontal Plus) 247 reports · 3.7% of its reports
Underdose after Pyrantel 82 reports · 1.7% of its reports
Underdose after Praziquantel + Pyrantel 65 reports · 1.8% of its reports
Underdose after Praziquantel 28 reports · 2.5% of its reports

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