Didn't stop worms after Fenbendazole in dogs

The FDA has received 1,224 reports of didn't stop worms in dogs after Fenbendazole. That is 21% of all reports for this medicine, compared with 8.4% across reports for all dog medicines, so it is reported unusually often with this medicine.

1,224Reports
44%Marked serious
8.7%Recovered
2.5%Died or euthanised
37 daysTypical onset
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How soon it started

Same day
69 8.4%
1–2 days
18 2.2%
3–7 days
57 7.0%
1–4 weeks
228 28%
Over a month
448 55%

How the animals did

Recovered
105 8.6%
Recovered with lasting effects
2 0.2%
Still unwell when reported
556 45%
Died
23 1.9%
Euthanised
7 0.6%
Not known
531 43%

Problems reported at the same time

Didn't work as expected
117 9.6%
Diarrhea
80 6.5%
Vomiting
72 5.9%
Overdose
40 3.3%
Loss of appetite
34 2.8%
Underdose
33 2.7%
Death
30 2.5%
Drug administration error
28 2.3%

Age of the animals

Under 1 year
443
1–3 years
328
4–7 years
185
8–11 years
97
12+ years
50

About this medicine

Fenbendazole treats intestinal worms and some other parasites.

Questions owners ask

Can Fenbendazole cause didn't stop worms in dogs?
1,224 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 37 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).

Didn't stop worms with similar medicines

All reported side effects of Fenbendazole in dogs · Medicines most reported with didn't stop worms