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

The FDA has received 438 reports of didn't stop ticks in dogs after Ivermectin + Pyrantel. That is 0.3% of all reports for this medicine, compared with 2.3% across reports for all dog medicines, so it is reported less often than average with this medicine.

438Reports

18%Marked serious

16%Recovered

1.8%Died or euthanised

20 daysTypical onset

How soon it started

Same day

11 5.5%

1–2 days

18 9.0%

3–7 days

18 9.0%

1–4 weeks

78 39%

Over a month

74 37%

How the animals did

Recovered

65 15%

Recovered with lasting effects

3 0.7%

Still unwell when reported

113 26%

Died

4 0.9%

Euthanised

4 0.9%

Not known

249 57%

Problems reported at the same time

Didn't work as expected

251 57%

Didn't prevent heartworm

24 5.5%

12 2.7%

12 2.7%

11 2.5%

10 2.3%

10 2.3%

8 1.8%

Age of the animals

Under 1 year

1–3 years

177

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 ticks in dogs?: 438 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 ticks with similar medicines

Didn't stop ticks after Milbemycin Oxime + Spinosad (Trifexis) 312 reports · 0.2% of its reports
Didn't stop ticks after Milbemycin Oxime + Praziquantel (Interceptor Plus) 311 reports · 1.0% of its reports
Didn't stop ticks after Milbemycin Oxime (Interceptor) 41 reports · 0.1% of its reports
Didn't stop ticks after Selamectin (Revolution) 1,191 reports · 4.1% of its reports
Didn't stop ticks after Ivermectin (Heartgard) 38 reports · 0.3% of its reports

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