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

The FDA has received 32,467 reports of didn't stop worms in dogs after Ivermectin + Pyrantel. That is 22% of all reports for this medicine, compared with 8.4% across reports for all dog medicines, so it is reported unusually often with this medicine.

32,467Reports

35%Marked serious

3.4%Recovered

0.2%Died or euthanised

23 daysTypical onset

How soon it started

Same day

186 1.2%

1–2 days

805 5.2%

3–7 days

1,690 11%

1–4 weeks

7,682 49%

Over a month

5,184 33%

How the animals did

Recovered

1,068 3.3%

Recovered with lasting effects

20 0.1%

Still unwell when reported

3,290 10%

Died

42 0.1%

Euthanised

16 0.0%

Not known

28,031 86%

Problems reported at the same time

Digestive tract disorder

10,665 33%

Didn't work as expected

6,947 21%

Diarrhea

1,972 6.1%

Vomiting

858 2.6%

Loose stool

404 1.2%

Drug dose administration interval too long

401 1.2%

Loss of appetite

371 1.1%

Underdose

353 1.1%

Age of the animals

Under 1 year

3,207

1–3 years

11,457

4–7 years

9,249

8–11 years

5,636

12+ years

1,710

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 worms in dogs?: 32,467 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 worms with similar medicines

Didn't stop worms after Milbemycin Oxime + Spinosad (Trifexis) 4,483 reports · 3.5% of its reports
Didn't stop worms after Moxidectin (ProHeart 6) 9,537 reports · 19% of its reports
Didn't stop worms after Milbemycin Oxime + Praziquantel (Interceptor Plus) 6,097 reports · 19% of its reports
Didn't stop worms after Milbemycin Oxime (Interceptor) 4,308 reports · 14% of its reports
Didn't stop worms after Selamectin (Revolution) 2,317 reports · 7.9% of its reports
Didn't stop worms after Ivermectin (Heartgard) 254 reports · 2.1% of its reports
Didn't stop worms after Ivermectin + Praziquantel + Pyrantel (Iverhart Max) 1,299 reports · 15% of its reports
Didn't stop worms after Moxidectin + Pyrantel + Sarolaner (Simparica Trio) 132 reports · 11% of its reports

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