Lethargy after Fenbendazole in cats

The FDA has received 56 reports of lethargy in cats after Fenbendazole. That is 20% of all reports for this medicine, compared with 14% across reports for all cat medicines.

56Reports

50%Marked serious

21%Recovered

16%Died or euthanised

1 daysTypical onset

How soon it started

Same day

14 30%

1–2 days

12 26%

3–7 days

6 13%

1–4 weeks

12 26%

Over a month

2 4.3%

How the animals did

Recovered

12 21%

Still unwell when reported

13 23%

Died

8 14%

Euthanised

1 1.8%

Not known

22 39%

Problems reported at the same time

22 39%

15 27%

10 18%

9 16%

6 11%

Hypoglycaemia

6 11%

Breathing problems

6 11%

Weakness

5 8.9%

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 lethargy in cats?: 56 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).

Lethargy with similar medicines

Lethargy after Emodepside + Praziquantel (Profender) 909 reports · 16% of its reports
Lethargy after Praziquantel 226 reports · 14% of its reports
Lethargy after Praziquantel + Pyrantel 213 reports · 17% of its reports
Lethargy after Pyrantel 159 reports · 28% of its reports

All reported side effects of Fenbendazole in cats · Medicines most reported with lethargy