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

The FDA has received 117 reports of didn't stop ticks in dogs after Fipronil + S-methoprene. That is 4.0% of all reports for this medicine, compared with 2.3% across reports for all dog medicines, so it is reported unusually often with this medicine.

117Reports

29%Marked serious

11%Recovered

1.7%Died or euthanised

16 daysTypical onset

How soon it started

Same day

13 20%

1–2 days

4 6.3%

3–7 days

3 4.7%

1–4 weeks

26 41%

Over a month

18 28%

How the animals did

Recovered

13 11%

Still unwell when reported

14 12%

Died

1 0.9%

Euthanised

1 0.9%

Not known

88 75%

Problems reported at the same time

Didn't work as expected

55 47%

20 17%

9 7.7%

6 5.1%

3 2.6%

3 2.6%

3 2.6%

2 1.7%

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 didn't stop ticks in dogs?: 117 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 16 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 ticks with similar medicines

Didn't stop ticks after Spinosad (Comfortis) 95 reports · 0.2% of its reports
Didn't stop ticks after Lufenuron + Milbemycin Oxime (Sentinel) 42 reports · 0.2% of its reports
Didn't stop ticks after Imidacloprid + Moxidectin (Advantage Multi) 52 reports · 0.4% of its reports
Didn't stop ticks after Nitenpyram (Capstar) 51 reports · 0.5% of its reports
Didn't stop ticks after Lufenuron + Milbemycin Oxime + Praziquantel (Sentinel Spectrum) 36 reports · 0.4% of its reports
Didn't stop ticks after Flumethrin + Imidacloprid (Seresto) 158 reports · 7.0% of its reports
Didn't stop ticks after Imidacloprid + Permethrin + Pyriproxyfen 21 reports · 2.8% of its reports
Didn't stop ticks after Fipronil + Pyriproxyfen + S-methoprene 33 reports · 7.7% of its reports

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