Didn't stop fleas after Fipronil + S-methoprene (Frontline Plus) in dogs

The FDA has received 576 reports of didn't stop fleas in dogs after Fipronil + S-methoprene. That is 19% of all reports for this medicine, compared with 6.2% across reports for all dog medicines, so it is reported unusually often with this medicine.

576Reports

19%Marked serious

7.5%Recovered

0.3%Died or euthanised

20 daysTypical onset

How soon it started

Same day

24 5.7%

1–2 days

60 14%

3–7 days

44 10%

1–4 weeks

135 32%

Over a month

157 37%

How the animals did

Recovered

42 7.3%

Recovered with lasting effects

1 0.2%

Still unwell when reported

49 8.5%

Died

1 0.2%

Euthanised

1 0.2%

Not known

482 84%

Problems reported at the same time

Didn't work as expected

79 14%

Skin disorders

71 12%

Itching

59 10%

Overdose

11 1.9%

Hair loss

10 1.7%

Restlessness or agitation

9 1.6%

Didn't stop ticks

9 1.6%

Underdose

8 1.4%

Age of the animals

Under 1 year

1–3 years

102

4–7 years

144

8–11 years

113

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 didn't stop fleas in dogs?: 576 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 20 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 Spinosad (Comfortis) 13,280 reports · 23% of its reports
Didn't stop fleas after Lufenuron + Milbemycin Oxime (Sentinel) 977 reports · 3.8% of its reports
Didn't stop fleas after Imidacloprid + Moxidectin (Advantage Multi) 1,444 reports · 11% of its reports
Didn't stop fleas after Nitenpyram (Capstar) 6,142 reports · 57% of its reports
Didn't stop fleas after Lufenuron + Milbemycin Oxime + Praziquantel (Sentinel Spectrum) 498 reports · 5.0% of its reports
Didn't stop fleas after Flumethrin + Imidacloprid (Seresto) 882 reports · 39% of its reports
Didn't stop fleas after Imidacloprid 1,054 reports · 55% of its reports
Didn't stop fleas after Fipronil 394 reports · 28% of its reports
Didn't stop fleas after Lufenuron 44 reports · 4.3% of its reports
Didn't stop fleas after Imidacloprid + Permethrin + Pyriproxyfen 219 reports · 30% of its reports

All reported side effects of Fipronil + S-methoprene in dogs · Medicines most reported with didn't stop fleas