Loose stool after Milbemycin Oxime + Spinosad (Trifexis) in dogs

The FDA has received 885 reports of loose stool in dogs after Milbemycin Oxime + Spinosad. That is 0.7% of all reports for this medicine, compared with 0.9% across reports for all dog medicines.

885Reports

25%Marked serious

51%Recovered

3.5%Died or euthanised

4 daysTypical onset

How soon it started

Same day

241 37%

1–2 days

77 12%

3–7 days

16 2.5%

1–4 weeks

55 8.5%

Over a month

258 40%

How the animals did

Recovered

340 38%

Recovered with lasting effects

115 13%

Still unwell when reported

117 13%

Died

16 1.8%

Euthanised

15 1.7%

Not known

282 32%

Problems reported at the same time

Vomiting

417 47%

Lethargy

300 34%

Loss of appetite

207 23%

Didn't work as expected

179 20%

147 17%

97 11%

65 7.3%

59 6.7%

Age of the animals

Under 1 year

181

1–3 years

258

4–7 years

205

8–11 years

155

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 loose stool in dogs?: 885 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 4 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).

Loose stool with similar medicines

Loose stool after Ivermectin + Pyrantel (Heartgard Plus) 1,339 reports · 0.9% of its reports
Loose stool after Moxidectin (ProHeart 6) 332 reports · 0.7% of its reports
Loose stool after Milbemycin Oxime + Praziquantel (Interceptor Plus) 406 reports · 1.3% of its reports
Loose stool after Milbemycin Oxime (Interceptor) 327 reports · 1.1% of its reports
Loose stool after Selamectin (Revolution) 156 reports · 0.5% of its reports
Loose stool after Ivermectin (Heartgard) 88 reports · 0.7% of its reports
Loose stool after Ivermectin + Praziquantel + Pyrantel (Iverhart Max) 120 reports · 1.4% of its reports

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