Didn't stop fleas after Ivermectin (Heartgard) in dogs

451 reports to the FDA describe didn't stop fleas in dogs given Ivermectin. That is 3.8% of all reports for this medicine, compared with 6.2% across reports for all dog medicines, so it is reported less often than average with this medicine.

451Reports

5.3%Marked serious

21%Recovered

0.4%Died or euthanised

126 daysTypical onset

How soon it started

Same day

11 5.3%

1–2 days

6 2.9%

3–7 days

3 1.4%

1–4 weeks

28 14%

Over a month

159 77%

How the animals did

Recovered

50 11%

Recovered with lasting effects

43 9.5%

Still unwell when reported

8 1.8%

Euthanised

2 0.4%

Not known

348 77%

Problems reported at the same time

Itching

73 16%

Didn't work as expected

62 14%

52 12%

27 6.0%

15 3.3%

15 3.3%

14 3.1%

12 2.7%

Age of the animals

Under 1 year

1–3 years

118

4–7 years

154

8–11 years

12+ years

About this medicine

Ivermectin prevents heartworm disease (monthly).

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

Some herding breeds (for example Collies) carry the MDR1 gene variant and can be more sensitive to this drug class at high doses.

Questions owners ask

Can Ivermectin cause didn't stop fleas in dogs?: 451 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 126 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 Ivermectin + Pyrantel (Heartgard Plus) 483 reports · 0.3% of its reports
Didn't stop fleas after Milbemycin Oxime + Spinosad (Trifexis) 8,717 reports · 6.7% of its reports
Didn't stop fleas after Moxidectin (ProHeart 6) 70 reports · 0.1% of its reports
Didn't stop fleas after Milbemycin Oxime + Praziquantel (Interceptor Plus) 171 reports · 0.5% of its reports
Didn't stop fleas after Milbemycin Oxime (Interceptor) 118 reports · 0.4% of its reports
Didn't stop fleas after Selamectin (Revolution) 3,379 reports · 11% of its reports
Didn't stop fleas after Ivermectin + Praziquantel + Pyrantel (Iverhart Max) 38 reports · 0.4% of its reports
Didn't stop fleas after Moxidectin + Pyrantel + Sarolaner (Simparica Trio) 21 reports · 1.8% of its reports

All reported side effects of Ivermectin in dogs · Medicines most reported with didn't stop fleas