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

8,717 reports to the FDA describe didn't stop fleas in dogs given Milbemycin Oxime + Spinosad. That is 6.7% of all reports for this medicine, compared with 6.2% across reports for all dog medicines.

8,717Reports

3.2%Marked serious

13%Recovered

0.3%Died or euthanised

29 daysTypical onset

How soon it started

Same day

934 18%

1–2 days

140 2.6%

3–7 days

298 5.6%

1–4 weeks

1,360 26%

Over a month

2,575 49%

How the animals did

Recovered

538 6.2%

Recovered with lasting effects

632 7.3%

Still unwell when reported

367 4.2%

Died

18 0.2%

Euthanised

9 0.1%

Not known

7,153 82%

Problems reported at the same time

Didn't work as expected

4,846 56%

1,060 12%

740 8.5%

450 5.2%

162 1.9%

Skin rash or irritation

159 1.8%

Lethargy

152 1.7%

Hair loss

97 1.1%

Age of the animals

Under 1 year

1,092

1–3 years

2,340

4–7 years

2,255

8–11 years

1,277

12+ years

476

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 fleas in dogs?: 8,717 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 29 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 fleas with similar medicines

Didn't stop fleas after Ivermectin + Pyrantel (Heartgard Plus) 483 reports · 0.3% of its reports
Didn't stop fleas after Moxidectin (ProHeart 6) 70 reports · 0.1% of its reports
Didn't stop fleas after Milbemycin Oxime + Praziquantel (Interceptor Plus) 171 reports · 0.5% of its reports
Didn't stop fleas after Milbemycin Oxime (Interceptor) 118 reports · 0.4% of its reports
Didn't stop fleas after Selamectin (Revolution) 3,379 reports · 11% of its reports
Didn't stop fleas after Ivermectin (Heartgard) 451 reports · 3.8% of its reports
Didn't stop fleas after Ivermectin + Praziquantel + Pyrantel (Iverhart Max) 38 reports · 0.4% of its reports
Didn't stop fleas after Moxidectin + Pyrantel + Sarolaner (Simparica Trio) 21 reports · 1.8% of its reports

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