Monocytosis after Milbemycin Oxime + Spinosad (Trifexis) in dogs

96 reports to the FDA describe monocytosis in dogs given 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.

96Reports

86%Marked serious

32%Recovered

15%Died or euthanised

1 daysTypical onset

How soon it started

Same day

23 34%

1–2 days

11 16%

3–7 days

5 7.5%

1–4 weeks

8 12%

Over a month

20 30%

How the animals did

Recovered

12 13%

Recovered with lasting effects

19 20%

Still unwell when reported

28 29%

Died

8 8.3%

Euthanised

6 6.3%

Not known

23 24%

Problems reported at the same time

65 68%

63 66%

61 64%

57 59%

51 53%

51 53%

36 38%

33 34%

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 monocytosis in dogs?: 96 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 1 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).

Monocytosis with similar medicines

Monocytosis after Ivermectin + Pyrantel (Heartgard Plus) 185 reports · 0.1% of its reports
Monocytosis after Moxidectin (ProHeart 6) 177 reports · 0.3% of its reports
Monocytosis after Milbemycin Oxime + Praziquantel (Interceptor Plus) 76 reports · 0.2% of its reports
Monocytosis after Milbemycin Oxime (Interceptor) 29 reports · 0.1% of its reports
Monocytosis after Selamectin (Revolution) 36 reports · 0.1% of its reports
Monocytosis after Ivermectin (Heartgard) 31 reports · 0.3% of its reports

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