Didn't stop fleas after Flumethrin + Imidacloprid (Seresto) in cats

The FDA has received 255 reports of didn't stop fleas in cats after Flumethrin + Imidacloprid. 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.

255Reports
16%Marked serious
2.4%Recovered
2.4%Died or euthanised
43 daysTypical onset
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How soon it started

Same day
7 3.5%
1–2 days
21 11%
3–7 days
10 5.0%
1–4 weeks
43 22%
Over a month
118 59%

How the animals did

Recovered
6 2.4%
Still unwell when reported
23 9.0%
Died
5 2.0%
Euthanised
1 0.4%
Not known
220 86%

Problems reported at the same time

Itching
75 29%
Application site reaction
26 10%
Hair loss
24 9.4%
Behaviour change
16 6.3%
Vomiting
11 4.3%
Lethargy
10 3.9%
Hiding
9 3.5%
Didn't stop worms
8 3.1%

Age of the animals

Under 1 year
19
1–3 years
56
4–7 years
51
8–11 years
29
12+ years
36

About this medicine

Imidacloprid kills fleas (spot-on or collar).

Products with this combination include Seresto. The FDA hides brand names in its public data, so these reports cover every product with the same active ingredients.

Questions owners ask

Can Flumethrin + Imidacloprid cause didn't stop fleas in cats?
255 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 43 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 Flumethrin + Imidacloprid in cats · Medicines most reported with didn't stop fleas