Hair loss after Milbemycin Oxime + Spinosad (Trifexis) in dogs

The FDA has received 1,029 reports of hair loss in dogs after Milbemycin Oxime + Spinosad. That is 0.8% of all reports for this medicine, compared with 1.0% across reports for all dog medicines.

1,029Reports

22%Marked serious

43%Recovered

2.5%Died or euthanised

7 daysTypical onset

How soon it started

Same day

255 32%

1–2 days

70 8.8%

3–7 days

72 9.1%

1–4 weeks

89 11%

Over a month

306 39%

How the animals did

Recovered

150 15%

Recovered with lasting effects

295 29%

Still unwell when reported

249 24%

Died

10 1.0%

Euthanised

16 1.6%

Not known

309 30%

Problems reported at the same time

Itching

455 44%

Vomiting

176 17%

Skin rash or irritation

154 15%

Lethargy

144 14%

Loss of appetite

108 10%

Reddening of the skin

98 9.5%

Didn't stop fleas

97 9.4%

Skin redness

86 8.4%

Age of the animals

Under 1 year

167

1–3 years

318

4–7 years

272

8–11 years

165

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 hair loss in dogs?: 1,029 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 7 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).

Hair loss with similar medicines

Hair loss after Ivermectin + Pyrantel (Heartgard Plus) 539 reports · 0.4% of its reports
Hair loss after Moxidectin (ProHeart 6) 325 reports · 0.6% of its reports
Hair loss after Milbemycin Oxime + Praziquantel (Interceptor Plus) 158 reports · 0.5% of its reports
Hair loss after Milbemycin Oxime (Interceptor) 132 reports · 0.4% of its reports
Hair loss after Selamectin (Revolution) 1,036 reports · 3.5% of its reports
Hair loss after Ivermectin (Heartgard) 104 reports · 0.9% of its reports
Hair loss after Ivermectin + Praziquantel + Pyrantel (Iverhart Max) 20 reports · 0.2% of its reports

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