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

The FDA has received 483 reports of didn't stop fleas in dogs after Ivermectin + Pyrantel. That is 0.3% 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.

483Reports

8.3%Marked serious

13%Recovered

0.4%Died or euthanised

23 daysTypical onset

How soon it started

Same day

10 3.1%

1–2 days

26 8.2%

3–7 days

34 11%

1–4 weeks

123 39%

Over a month

125 39%

How the animals did

Recovered

41 8.5%

Recovered with lasting effects

22 4.6%

Still unwell when reported

26 5.4%

Died

1 0.2%

Euthanised

1 0.2%

Not known

392 81%

Problems reported at the same time

Itching

56 12%

Didn't work as expected

34 7.0%

26 5.4%

16 3.3%

14 2.9%

13 2.7%

10 2.1%

10 2.1%

Age of the animals

Under 1 year

1–3 years

133

4–7 years

137

8–11 years

12+ years

About this medicine

Ivermectin prevents heartworm disease (monthly). Pyrantel treats roundworms and hookworms.

Products with this combination include Heartgard Plus, Tri-Heart Plus, Iverhart Plus. 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 + Pyrantel cause didn't stop fleas in dogs?: 483 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).

Didn't stop fleas with similar medicines

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 (Heartgard) 451 reports · 3.8% 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 + Pyrantel in dogs · Medicines most reported with didn't stop fleas