Didn't prevent heartworm after Ivermectin (Heartgard) in dogs

3,385 reports to the FDA describe didn't prevent heartworm in dogs given Ivermectin. That is 28% of all reports for this medicine, compared with 13% across reports for all dog medicines, so it is reported unusually often with this medicine.

3,385Reports

37%Marked serious

5.3%Recovered

0.6%Died or euthanised

263 daysTypical onset

How soon it started

Same day

11 1.4%

1–2 days

2 0.3%

3–7 days

4 0.5%

1–4 weeks

11 1.4%

Over a month

752 96%

How the animals did

Recovered

106 3.1%

Recovered with lasting effects

75 2.2%

Still unwell when reported

1,480 44%

Died

15 0.4%

Euthanised

6 0.2%

Not known

1,703 50%

Problems reported at the same time

Didn't work as expected

280 8.3%

69 2.0%

52 1.5%

46 1.4%

38 1.1%

34 1.0%

33 1.0%

Drug dose administration interval too long

31 0.9%

Age of the animals

Under 1 year

1–3 years

1,850

4–7 years

966

8–11 years

378

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 prevent heartworm in dogs?: 3,385 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 263 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 prevent heartworm with similar medicines

Didn't prevent heartworm after Ivermectin + Pyrantel (Heartgard Plus) 57,581 reports · 39% of its reports
Didn't prevent heartworm after Milbemycin Oxime + Spinosad (Trifexis) 10,801 reports · 8.3% of its reports
Didn't prevent heartworm after Moxidectin (ProHeart 6) 11,529 reports · 23% of its reports
Didn't prevent heartworm after Milbemycin Oxime + Praziquantel (Interceptor Plus) 8,433 reports · 27% of its reports
Didn't prevent heartworm after Milbemycin Oxime (Interceptor) 13,118 reports · 44% of its reports
Didn't prevent heartworm after Selamectin (Revolution) 8,789 reports · 30% of its reports
Didn't prevent heartworm after Ivermectin + Praziquantel + Pyrantel (Iverhart Max) 1,879 reports · 22% of its reports
Didn't prevent heartworm after Moxidectin + Pyrantel + Sarolaner (Simparica Trio) 319 reports · 28% of its reports

All reported side effects of Ivermectin in dogs · Medicines most reported with didn't prevent heartworm