Reddening of the skin after Fipronil + S-methoprene (Frontline Plus) in dogs

26 reports to the FDA describe reddening of the skin in dogs given Fipronil + S-methoprene. That is 0.9% of all reports for this medicine, compared with 0.4% across reports for all dog medicines, so it is reported unusually often with this medicine.

26Reports

50%Marked serious

23%Recovered

3.8%Died or euthanised

29 daysTypical onset

How soon it started

Same day

3 18%

1–2 days

2 12%

3–7 days

2 12%

1–4 weeks

2 12%

Over a month

8 47%

How the animals did

Recovered

5 19%

Recovered with lasting effects

1 3.8%

Still unwell when reported

3 12%

Euthanised

1 3.8%

Not known

16 62%

Problems reported at the same time

14 54%

4 15%

4 15%

3 12%

3 12%

3 12%

3 12%

Self trauma

3 12%

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 reddening of the skin in dogs?: 26 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 29 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).

Reddening of the skin with similar medicines

Reddening of the skin after Spinosad (Comfortis) 222 reports · 0.4% of its reports
Reddening of the skin after Lufenuron + Milbemycin Oxime (Sentinel) 51 reports · 0.2% of its reports
Reddening of the skin after Imidacloprid + Moxidectin (Advantage Multi) 43 reports · 0.3% of its reports
Reddening of the skin after Nitenpyram (Capstar) 90 reports · 0.8% of its reports
Reddening of the skin after Lufenuron + Milbemycin Oxime + Praziquantel (Sentinel Spectrum) 21 reports · 0.2% of its reports

All reported side effects of Fipronil + S-methoprene in dogs · Medicines most reported with reddening of the skin