Didn't prevent heartworm after Milbemycin Oxime (Interceptor) in dogs

The FDA has received 13,118 reports of didn't prevent heartworm in dogs after Milbemycin Oxime. That is 44% of all reports for this medicine, compared with 13% across reports for all dog medicines, so it is reported unusually often with this medicine.

13,118Reports

12%Marked serious

1.6%Recovered

1.7%Died or euthanised

270 daysTypical onset

How soon it started

Same day

5 1.0%

1–2 days

3 0.6%

3–7 days

5 1.0%

1–4 weeks

19 3.8%

Over a month

467 94%

How the animals did

Recovered

190 1.4%

Recovered with lasting effects

16 0.1%

Still unwell when reported

1,692 13%

Died

207 1.6%

Euthanised

14 0.1%

Not known

10,999 84%

Problems reported at the same time

Didn't work as expected

283 2.2%

218 1.7%

97 0.7%

77 0.6%

56 0.4%

54 0.4%

52 0.4%

49 0.4%

Age of the animals

Under 1 year

1–3 years

6,213

4–7 years

4,300

8–11 years

1,959

12+ years

373

About this medicine

Milbemycin Oxime prevents heartworm and controls some intestinal worms (monthly).

Products with this ingredient include Interceptor. 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 Milbemycin Oxime cause didn't prevent heartworm in dogs?: 13,118 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 270 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 Selamectin (Revolution) 8,789 reports · 30% of its reports
Didn't prevent heartworm after Ivermectin (Heartgard) 3,385 reports · 28% 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 Milbemycin Oxime in dogs · Medicines most reported with didn't prevent heartworm