Skin sore after Milbemycin Oxime + Spinosad (Trifexis) in dogs

The FDA has received 187 reports of skin sore in dogs after Milbemycin Oxime + Spinosad. That is 0.1% of all reports for this medicine, compared with 0.1% across reports for all dog medicines.

187Reports

21%Marked serious

40%Recovered

4.3%Died or euthanised

7 daysTypical onset

How soon it started

Same day

48 35%

1–2 days

14 10%

3–7 days

9 6.6%

1–4 weeks

15 11%

Over a month

51 37%

How the animals did

Recovered

20 11%

Recovered with lasting effects

54 29%

Still unwell when reported

44 24%

Died

3 1.6%

Euthanised

5 2.7%

Not known

61 33%

Problems reported at the same time

Itching

85 45%

Didn't stop fleas

46 25%

Didn't work as expected

39 21%

Hair loss

39 21%

Lethargy

31 17%

Vomiting

30 16%

Skin rash or irritation

26 14%

Loss of appetite

18 9.6%

Age of the animals

Under 1 year

1–3 years

4–7 years

8–11 years

12+ years

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 skin sore in dogs?: 187 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 7 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).

Skin sore with similar medicines

Skin sore after Ivermectin + Pyrantel (Heartgard Plus) 84 reports · 0.1% of its reports
Skin sore after Moxidectin (ProHeart 6) 21 reports · 0.0% of its reports
Skin sore after Milbemycin Oxime + Praziquantel (Interceptor Plus) 33 reports · 0.1% of its reports
Skin sore after Selamectin (Revolution) 47 reports · 0.2% of its reports

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