Lethargy after Milbemycin Oxime + Spinosad (Trifexis) in dogs

19,835 reports to the FDA describe lethargy in dogs given Milbemycin Oxime + Spinosad. That is 15% of all reports for this medicine, compared with 11% across reports for all dog medicines.

19,835Reports

18%Marked serious

65%Recovered

3.4%Died or euthanised

Same dayTypical onset

How soon it started

Same day

8,862 56%

1–2 days

2,015 13%

3–7 days

342 2.2%

1–4 weeks

640 4.0%

Over a month

3,952 25%

How the animals did

Recovered

10,647 54%

Recovered with lasting effects

2,159 11%

Still unwell when reported

1,877 9.5%

Died

372 1.9%

Euthanised

310 1.6%

Not known

4,470 23%

Problems reported at the same time

9,216 46%

5,012 25%

2,730 14%

2,033 10%

1,855 9.4%

1,405 7.1%

1,082 5.5%

897 4.5%

Age of the animals

Under 1 year

3,561

1–3 years

7,411

4–7 years

4,745

8–11 years

2,450

12+ years

942

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 lethargy in dogs?: 19,835 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 the same day 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).

Lethargy with similar medicines

Lethargy after Ivermectin + Pyrantel (Heartgard Plus) 7,391 reports · 5.0% of its reports
Lethargy after Moxidectin (ProHeart 6) 6,640 reports · 13% of its reports
Lethargy after Milbemycin Oxime + Praziquantel (Interceptor Plus) 2,407 reports · 7.6% of its reports
Lethargy after Milbemycin Oxime (Interceptor) 2,528 reports · 8.5% of its reports
Lethargy after Selamectin (Revolution) 2,964 reports · 10% of its reports
Lethargy after Ivermectin (Heartgard) 1,488 reports · 12% of its reports
Lethargy after Ivermectin + Praziquantel + Pyrantel (Iverhart Max) 969 reports · 11% of its reports
Lethargy after Moxidectin + Pyrantel + Sarolaner (Simparica Trio) 135 reports · 12% of its reports
Lethargy after Ivermectin + Praziquantel 35 reports · 17% of its reports
Lethargy after Moxidectin + Praziquantel 21 reports · 28% of its reports

All reported side effects of Milbemycin Oxime + Spinosad in dogs · Medicines most reported with lethargy