Itching after Fipronil + S-methoprene (Frontline Plus) in cats

The FDA has received 68 reports of itching in cats after Fipronil + S-methoprene. That is 19% of all reports for this medicine, compared with 8.9% across reports for all cat medicines, so it is reported unusually often with this medicine.

68Reports

22%Marked serious

16%Recovered

2.9%Died or euthanised

7 daysTypical onset

How soon it started

Same day

6 11%

1–2 days

8 14%

3–7 days

15 26%

1–4 weeks

21 37%

Over a month

7 12%

How the animals did

Recovered

11 16%

Still unwell when reported

16 24%

Euthanised

2 2.9%

Not known

39 57%

Problems reported at the same time

Restlessness or agitation

15 22%

Didn't stop fleas

14 21%

Hair loss

12 18%

Behaviour change

12 18%

Licking

6 8.8%

Loss of appetite

5 7.4%

Seizures

4 5.9%

Breathing problems

4 5.9%

Age of the animals

Under 1 year

1–3 years

4–7 years

8–11 years

12+ years

About this medicine

Fipronil kills fleas and ticks (spot-on).

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

Questions owners ask

Can Fipronil + S-methoprene cause itching in cats?: 68 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 7 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).

Itching with similar medicines

Itching after Spinosad (Comfortis) 439 reports · 3.8% of its reports
Itching after Nitenpyram (Capstar) 1,904 reports · 22% of its reports
Itching after Imidacloprid + Moxidectin (Advantage Multi) 1,531 reports · 19% of its reports
Itching after Lufenuron 84 reports · 7.6% of its reports
Itching after Flumethrin + Imidacloprid (Seresto) 210 reports · 31% of its reports
Itching after Imidacloprid + Pyriproxyfen 222 reports · 34% of its reports
Itching after Fipronil 63 reports · 13% of its reports
Itching after Imidacloprid 42 reports · 17% of its reports

All reported side effects of Fipronil + S-methoprene in cats · Medicines most reported with itching