Didn't stop worms after Milbemycin Oxime + Spinosad (Trifexis) in dogs

4,483 reports to the FDA describe didn't stop worms in dogs given Milbemycin Oxime + Spinosad. That is 3.5% of all reports for this medicine, compared with 8.4% across reports for all dog medicines, so it is reported less often than average with this medicine.

4,483Reports

9.6%Marked serious

11%Recovered

0.6%Died or euthanised

130 daysTypical onset

How soon it started

Same day

153 6.4%

1–2 days

20 0.8%

3–7 days

44 1.8%

1–4 weeks

244 10%

Over a month

1,930 81%

How the animals did

Recovered

299 6.7%

Recovered with lasting effects

182 4.1%

Still unwell when reported

247 5.5%

Died

16 0.4%

Euthanised

12 0.3%

Not known

3,727 83%

Problems reported at the same time

Didn't work as expected

2,781 62%

561 13%

411 9.2%

147 3.3%

147 3.3%

123 2.7%

110 2.5%

89 2.0%

Age of the animals

Under 1 year

564

1–3 years

1,456

4–7 years

1,134

8–11 years

800

12+ years

317

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 stop worms in dogs?: 4,483 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 130 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 worms with similar medicines

Didn't stop worms after Ivermectin + Pyrantel (Heartgard Plus) 32,467 reports · 22% of its reports
Didn't stop worms after Moxidectin (ProHeart 6) 9,537 reports · 19% of its reports
Didn't stop worms after Milbemycin Oxime + Praziquantel (Interceptor Plus) 6,097 reports · 19% of its reports
Didn't stop worms after Milbemycin Oxime (Interceptor) 4,308 reports · 14% of its reports
Didn't stop worms after Selamectin (Revolution) 2,317 reports · 7.9% of its reports
Didn't stop worms after Ivermectin (Heartgard) 254 reports · 2.1% of its reports
Didn't stop worms after Ivermectin + Praziquantel + Pyrantel (Iverhart Max) 1,299 reports · 15% of its reports
Didn't stop worms after Moxidectin + Pyrantel + Sarolaner (Simparica Trio) 132 reports · 11% of its reports

All reported side effects of Milbemycin Oxime + Spinosad in dogs · Medicines most reported with didn't stop worms