Weakness after Milbemycin Oxime + Spinosad (Trifexis) in dogs

847 reports to the FDA describe weakness in dogs given Milbemycin Oxime + Spinosad. That is 0.7% of all reports for this medicine, compared with 1.4% across reports for all dog medicines, so it is reported less often than average with this medicine.

847Reports
58%Marked serious
50%Recovered
19%Died or euthanised
1 daysTypical onset
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How soon it started

Same day
261 41%
1–2 days
84 13%
3–7 days
14 2.2%
1–4 weeks
62 9.8%
Over a month
210 33%

How the animals did

Recovered
297 35%
Recovered with lasting effects
123 15%
Still unwell when reported
121 14%
Died
70 8.3%
Euthanised
92 11%
Not known
144 17%

Problems reported at the same time

Age of the animals

Under 1 year
131
1–3 years
218
4–7 years
165
8–11 years
189
12+ years
122

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 weakness in dogs?
847 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).

Weakness with similar medicines

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