Leucopenia after Milbemycin Oxime + Spinosad (Trifexis) in dogs

The FDA has received 109 reports of leucopenia in dogs after Milbemycin Oxime + Spinosad. That is 0.1% of all reports for this medicine, compared with 0.3% across reports for all dog medicines, so it is reported less often than average with this medicine.

109Reports

70%Marked serious

32%Recovered

18%Died or euthanised

19 daysTypical onset

How soon it started

Same day

21 28%

1–2 days

6 8.0%

3–7 days

3 4.0%

1–4 weeks

12 16%

Over a month

33 44%

How the animals did

Recovered

14 13%

Recovered with lasting effects

21 19%

Still unwell when reported

27 25%

Died

7 6.4%

Euthanised

13 12%

Not known

27 25%

Problems reported at the same time

54 50%

52 48%

45 41%

43 39%

41 38%

32 29%

25 23%

24 22%

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 leucopenia in dogs?: 109 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 19 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).

Leucopenia with similar medicines

Leucopenia after Ivermectin + Pyrantel (Heartgard Plus) 100 reports · 0.1% of its reports
Leucopenia after Moxidectin (ProHeart 6) 198 reports · 0.4% of its reports
Leucopenia after Milbemycin Oxime + Praziquantel (Interceptor Plus) 25 reports · 0.1% of its reports
Leucopenia after Milbemycin Oxime (Interceptor) 40 reports · 0.1% of its reports
Leucopenia after Selamectin (Revolution) 47 reports · 0.2% of its reports
Leucopenia after Ivermectin (Heartgard) 35 reports · 0.3% of its reports

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