Didn't stop fleas after Imidacloprid + Pyriproxyfen in cats

The FDA has received 282 reports of didn't stop fleas in cats after Imidacloprid + Pyriproxyfen. That is 43% 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.

282Reports
15%Marked serious
5.3%Recovered
1.4%Died or euthanised
21 daysTypical onset
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How soon it started

Same day
8 4.4%
1–2 days
16 8.8%
3–7 days
23 13%
1–4 weeks
73 40%
Over a month
61 34%

How the animals did

Recovered
15 5.3%
Still unwell when reported
34 12%
Died
2 0.7%
Euthanised
2 0.7%
Not known
229 81%

Problems reported at the same time

Itching
109 39%
Hair loss
22 7.8%
Behaviour change
20 7.1%
Didn't work as expected
18 6.4%
Didn't stop worms
15 5.3%
Vocalising
10 3.5%
Skin scab
10 3.5%
Application site reaction
10 3.5%

Age of the animals

Under 1 year
28
1–3 years
57
4–7 years
51
8–11 years
40
12+ years
39

About this medicine

Imidacloprid kills fleas (spot-on or collar).

Questions owners ask

Can Imidacloprid + Pyriproxyfen cause didn't stop fleas in cats?
282 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 21 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 Imidacloprid + Pyriproxyfen in cats · Medicines most reported with didn't stop fleas