Drug dose omission after Milbemycin Oxime + Spinosad (Trifexis) in dogs

The FDA has received 1,201 reports of drug dose omission in dogs after Milbemycin Oxime + Spinosad. That is 0.9% of all reports for this medicine, compared with 0.4% across reports for all dog medicines, so it is reported unusually often with this medicine.

1,201Reports

8.8%Marked serious

8.8%Recovered

0.7%Died or euthanised

208 daysTypical onset

How soon it started

Same day

37 13%

1–2 days

2 0.7%

3–7 days

2 0.7%

1–4 weeks

12 4.3%

Over a month

223 81%

How the animals did

Recovered

86 7.2%

Recovered with lasting effects

20 1.7%

Still unwell when reported

72 6.0%

Died

7 0.6%

Euthanised

2 0.2%

Not known

1,014 84%

Problems reported at the same time

Didn't prevent heartworm

923 77%

Didn't work as expected

281 23%

162 13%

95 7.9%

84 7.0%

49 4.1%

42 3.5%

36 3.0%

Age of the animals

Under 1 year

1–3 years

510

4–7 years

356

8–11 years

214

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 drug dose omission in dogs?: 1,201 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 208 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).

Drug dose omission with similar medicines

Drug dose omission after Ivermectin + Pyrantel (Heartgard Plus) 503 reports · 0.3% of its reports
Drug dose omission after Moxidectin (ProHeart 6) 53 reports · 0.1% of its reports
Drug dose omission after Milbemycin Oxime + Praziquantel (Interceptor Plus) 399 reports · 1.3% of its reports
Drug dose omission after Milbemycin Oxime (Interceptor) 109 reports · 0.4% of its reports
Drug dose omission after Selamectin (Revolution) 87 reports · 0.3% of its reports
Drug dose omission after Ivermectin (Heartgard) 72 reports · 0.6% of its reports
Drug dose omission after Ivermectin + Praziquantel + Pyrantel (Iverhart Max) 87 reports · 1.0% of its reports

All reported side effects of Milbemycin Oxime + Spinosad in dogs · Medicines most reported with drug dose omission