Didn't stop fleas after Fipronil in cats

The FDA has received 190 reports of didn't stop fleas in cats after Fipronil. That is 38% of all reports for this medicine, compared with 8.4% across reports for all cat medicines, so it is reported unusually often with this medicine.

190Reports
4.7%Marked serious
6.3%Recovered
0.0%Died or euthanised
20 daysTypical onset
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How soon it started

Same day
4 4.0%
1–2 days
8 8.0%
3–7 days
12 12%
1–4 weeks
38 38%
Over a month
38 38%

How the animals did

Recovered
10 5.3%
Recovered with lasting effects
2 1.1%
Still unwell when reported
25 13%
Not known
153 81%

Problems reported at the same time

Didn't work as expected
27 14%
Itching
13 6.8%
Vomiting
8 4.2%
Lethargy
6 3.2%
Hair loss
5 2.6%
Application site reaction
5 2.6%
Hiding
5 2.6%
Restlessness or agitation
4 2.1%

Age of the animals

Under 1 year
11
1–3 years
55
4–7 years
35
8–11 years
32
12+ years
23

About this medicine

Fipronil kills fleas and ticks (spot-on).

Questions owners ask

Can Fipronil cause didn't stop fleas in cats?
190 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 20 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 fleas with similar medicines

All reported side effects of Fipronil in cats · Medicines most reported with didn't stop fleas