Didn't work as expected after Ivermectin (Heartgard) in dogs

The FDA has received 741 reports of didn't work as expected in dogs after Ivermectin. That is 6.2% of all reports for this medicine, compared with 13% across reports for all dog medicines, so it is reported less often than average with this medicine.

741Reports

25%Marked serious

11%Recovered

3.1%Died or euthanised

154 daysTypical onset

How soon it started

Same day

16 5.5%

1–2 days

12 4.1%

3–7 days

4 1.4%

1–4 weeks

32 11%

Over a month

226 78%

How the animals did

Recovered

60 8.1%

Recovered with lasting effects

20 2.7%

Still unwell when reported

294 40%

Died

11 1.5%

Euthanised

12 1.6%

Not known

344 46%

Problems reported at the same time

Didn't prevent heartworm

280 38%

62 8.4%

42 5.7%

32 4.3%

25 3.4%

25 3.4%

24 3.2%

22 3.0%

Age of the animals

Under 1 year

1–3 years

282

4–7 years

193

8–11 years

131

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 work as expected in dogs?: 741 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 154 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 work as expected with similar medicines

Didn't work as expected after Ivermectin + Pyrantel (Heartgard Plus) 27,781 reports · 19% of its reports
Didn't work as expected after Milbemycin Oxime + Spinosad (Trifexis) 13,050 reports · 10% of its reports
Didn't work as expected after Moxidectin (ProHeart 6) 2,005 reports · 4.0% of its reports
Didn't work as expected after Milbemycin Oxime + Praziquantel (Interceptor Plus) 3,979 reports · 13% of its reports
Didn't work as expected after Milbemycin Oxime (Interceptor) 3,131 reports · 11% of its reports
Didn't work as expected after Selamectin (Revolution) 2,253 reports · 7.7% of its reports
Didn't work as expected after Ivermectin + Praziquantel + Pyrantel (Iverhart Max) 1,337 reports · 16% of its reports
Didn't work as expected after Moxidectin + Pyrantel + Sarolaner (Simparica Trio) 123 reports · 11% of its reports

All reported side effects of Ivermectin in dogs · Medicines most reported with didn't work as expected