Lethargy after Fipronil + S-methoprene (Frontline Plus) in dogs

447 reports to the FDA describe lethargy in dogs given Fipronil + S-methoprene. That is 15% of all reports for this medicine, compared with 11% across reports for all dog medicines.

447Reports

64%Marked serious

49%Recovered

5.1%Died or euthanised

23 daysTypical onset

How soon it started

Same day

57 23%

1–2 days

25 10%

3–7 days

19 7.8%

1–4 weeks

33 13%

Over a month

111 45%

How the animals did

Recovered

214 48%

Recovered with lasting effects

7 1.6%

Still unwell when reported

34 7.6%

Died

8 1.8%

Euthanised

15 3.4%

Not known

169 38%

Problems reported at the same time

158 35%

118 26%

54 12%

44 9.8%

39 8.7%

36 8.1%

33 7.4%

28 6.3%

Age of the animals

Under 1 year

1–3 years

4–7 years

138

8–11 years

101

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 lethargy in dogs?: 447 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 23 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).

Lethargy with similar medicines

Lethargy after Spinosad (Comfortis) 7,303 reports · 13% of its reports
Lethargy after Lufenuron + Milbemycin Oxime (Sentinel) 2,341 reports · 9.0% of its reports
Lethargy after Imidacloprid + Moxidectin (Advantage Multi) 2,000 reports · 15% of its reports
Lethargy after Nitenpyram (Capstar) 1,204 reports · 11% of its reports
Lethargy after Lufenuron + Milbemycin Oxime + Praziquantel (Sentinel Spectrum) 666 reports · 6.7% of its reports
Lethargy after Flumethrin + Imidacloprid (Seresto) 250 reports · 11% of its reports
Lethargy after Imidacloprid 196 reports · 10% of its reports
Lethargy after Fipronil 185 reports · 13% of its reports
Lethargy after Lufenuron 205 reports · 20% of its reports
Lethargy after Imidacloprid + Permethrin + Pyriproxyfen 106 reports · 14% of its reports

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