Didn't prevent heartworm after Milbemycin Oxime + Spinosad (Trifexis) in dogs

10,801 reports to the FDA describe didn't prevent heartworm in dogs given Milbemycin Oxime + Spinosad. That is 8.3% 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.

10,801Reports

10.0%Marked serious

4.3%Recovered

0.7%Died or euthanised

256 daysTypical onset

How soon it started

Same day

173 5.8%

1–2 days

15 0.5%

3–7 days

23 0.8%

1–4 weeks

123 4.1%

Over a month

2,669 89%

How the animals did

Recovered

311 2.9%

Recovered with lasting effects

152 1.4%

Still unwell when reported

1,097 10%

Died

47 0.4%

Euthanised

25 0.2%

Not known

9,169 85%

Problems reported at the same time

Didn't work as expected

2,813 26%

923 8.5%

739 6.8%

353 3.3%

338 3.1%

316 2.9%

191 1.8%

175 1.6%

Age of the animals

Under 1 year

297

1–3 years

5,879

4–7 years

2,887

8–11 years

1,297

12+ years

286

About this medicine

Milbemycin Oxime prevents heartworm and controls some intestinal worms (monthly). Spinosad kills fleas; monthly chewable.

Products with this combination include Trifexis. 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 + Spinosad cause didn't prevent heartworm in dogs?: 10,801 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 256 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 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 (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 + Spinosad in dogs · Medicines most reported with didn't prevent heartworm