Didn't stop fleas after Spinosad (Comfortis) in cats

The FDA has received 1,841 reports of didn't stop fleas in cats after Spinosad. That is 16% 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.

1,841Reports

1.5%Marked serious

16%Recovered

0.2%Died or euthanised

15 daysTypical onset

How soon it started

Same day

383 25%

1–2 days

62 4.0%

3–7 days

119 7.6%

1–4 weeks

559 36%

Over a month

435 28%

How the animals did

Recovered

240 13%

Recovered with lasting effects

49 2.7%

Still unwell when reported

49 2.7%

Died

2 0.1%

Euthanised

2 0.1%

Not known

1,499 81%

Problems reported at the same time

Didn't work as expected

1,019 55%

385 21%

164 8.9%

129 7.0%

60 3.3%

51 2.8%

50 2.7%

28 1.5%

Age of the animals

Under 1 year

191

1–3 years

410

4–7 years

343

8–11 years

250

12+ years

230

About this medicine

Spinosad kills fleas; monthly chewable.

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

Questions owners ask

Can Spinosad cause didn't stop fleas in cats?: 1,841 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 15 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

Didn't stop fleas after Nitenpyram (Capstar) 2,325 reports · 27% of its reports
Didn't stop fleas after Imidacloprid + Moxidectin (Advantage Multi) 1,073 reports · 13% of its reports
Didn't stop fleas after Lufenuron 89 reports · 8.0% of its reports
Didn't stop fleas after Flumethrin + Imidacloprid (Seresto) 255 reports · 38% of its reports
Didn't stop fleas after Imidacloprid + Pyriproxyfen 282 reports · 43% of its reports
Didn't stop fleas after Fipronil 190 reports · 38% of its reports
Didn't stop fleas after Fipronil + S-methoprene (Frontline Plus) 134 reports · 37% of its reports
Didn't stop fleas after Imidacloprid 104 reports · 41% of its reports

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