Itching after Milbemycin Oxime + Spinosad (Trifexis) in dogs

6,069 reports to the FDA describe itching in dogs given Milbemycin Oxime + Spinosad. That is 4.7% of all reports for this medicine, compared with 4.3% across reports for all dog medicines.

6,069Reports

14%Marked serious

55%Recovered

1.2%Died or euthanised

2 daysTypical onset

How soon it started

Same day

2,026 43%

1–2 days

449 9.5%

3–7 days

248 5.2%

1–4 weeks

551 12%

Over a month

1,463 31%

How the animals did

Recovered

1,551 26%

Recovered with lasting effects

1,768 29%

Still unwell when reported

919 15%

Died

35 0.6%

Euthanised

35 0.6%

Not known

1,761 29%

Problems reported at the same time

Vomiting

1,294 21%

Didn't stop fleas

1,060 17%

Lethargy

897 15%

Didn't work as expected

884 15%

Loss of appetite

482 7.9%

Skin rash or irritation

461 7.6%

Hair loss

455 7.5%

Reddening of the skin

434 7.2%

Age of the animals

Under 1 year

775

1–3 years

1,925

4–7 years

1,761

8–11 years

891

12+ years

288

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 itching in dogs?: 6,069 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 2 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).

Itching with similar medicines

Itching after Ivermectin + Pyrantel (Heartgard Plus) 2,733 reports · 1.9% of its reports
Itching after Moxidectin (ProHeart 6) 2,435 reports · 4.8% of its reports
Itching after Milbemycin Oxime + Praziquantel (Interceptor Plus) 763 reports · 2.4% of its reports
Itching after Milbemycin Oxime (Interceptor) 563 reports · 1.9% of its reports
Itching after Selamectin (Revolution) 2,024 reports · 6.9% of its reports
Itching after Ivermectin (Heartgard) 528 reports · 4.4% of its reports
Itching after Ivermectin + Praziquantel + Pyrantel (Iverhart Max) 93 reports · 1.1% of its reports
Itching after Moxidectin + Pyrantel + Sarolaner (Simparica Trio) 57 reports · 4.9% of its reports

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