Underdose after Spinosad (Comfortis) in cats

159 reports to the FDA describe underdose in cats given Spinosad. That is 1.4% of all reports for this medicine, compared with 0.7% across reports for all cat medicines, so it is reported unusually often with this medicine.

159Reports

5.7%Marked serious

57%Recovered

3.8%Died or euthanised

Same dayTypical onset

How soon it started

Same day

70 53%

1–2 days

12 9.1%

3–7 days

9 6.8%

1–4 weeks

9 6.8%

Over a month

32 24%

How the animals did

Recovered

86 54%

Recovered with lasting effects

4 2.5%

Still unwell when reported

7 4.4%

Died

5 3.1%

Euthanised

1 0.6%

Not known

56 35%

Problems reported at the same time

Vomiting

97 61%

Didn't stop fleas

51 32%

Didn't work as expected

19 12%

14 8.8%

14 8.8%

12 7.5%

11 6.9%

6 3.8%

Age of the animals

Under 1 year

1–3 years

4–7 years

8–11 years

12+ years

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 underdose in cats?: 159 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 the same 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).

Underdose with similar medicines

Underdose after Nitenpyram (Capstar) 52 reports · 0.6% of its reports
Underdose after Imidacloprid + Moxidectin (Advantage Multi) 101 reports · 1.2% of its reports

All reported side effects of Spinosad in cats · Medicines most reported with underdose