Abnormal ultrasound finding after Milbemycin Oxime + Spinosad (Trifexis) in dogs

The FDA has received 240 reports of abnormal ultrasound finding in dogs after Milbemycin Oxime + Spinosad. That is 0.2% of all reports for this medicine, compared with 0.5% across reports for all dog medicines, so it is reported less often than average with this medicine.

240Reports

93%Marked serious

26%Recovered

29%Died or euthanised

28 daysTypical onset

How soon it started

Same day

39 26%

1–2 days

16 11%

3–7 days

6 4.0%

1–4 weeks

16 11%

Over a month

72 48%

How the animals did

Recovered

16 6.7%

Recovered with lasting effects

47 20%

Still unwell when reported

57 24%

Died

24 10%

Euthanised

46 19%

Not known

50 21%

Problems reported at the same time

163 68%

138 57%

123 51%

116 48%

72 30%

70 29%

64 27%

64 27%

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 abnormal ultrasound finding in dogs?: 240 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 28 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).

Abnormal ultrasound finding with similar medicines

Abnormal ultrasound finding after Ivermectin + Pyrantel (Heartgard Plus) 203 reports · 0.1% of its reports
Abnormal ultrasound finding after Moxidectin (ProHeart 6) 268 reports · 0.5% of its reports
Abnormal ultrasound finding after Milbemycin Oxime + Praziquantel (Interceptor Plus) 67 reports · 0.2% of its reports
Abnormal ultrasound finding after Milbemycin Oxime (Interceptor) 59 reports · 0.2% of its reports
Abnormal ultrasound finding after Selamectin (Revolution) 40 reports · 0.1% of its reports
Abnormal ultrasound finding after Ivermectin (Heartgard) 57 reports · 0.5% of its reports

All reported side effects of Milbemycin Oxime + Spinosad in dogs · Medicines most reported with abnormal ultrasound finding