Urinary retention after Milbemycin Oxime + Spinosad (Trifexis) in dogs

43 reports to the FDA describe urinary retention in dogs given Milbemycin Oxime + Spinosad. That is 0.0% of all reports for this medicine, compared with 0.0% across reports for all dog medicines.

43Reports
70%Marked serious
44%Recovered
14%Died or euthanised
1 daysTypical onset
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How soon it started

Same day
13 37%
1–2 days
7 20%
3–7 days
2 5.7%
1–4 weeks
2 5.7%
Over a month
11 31%

How the animals did

Recovered
14 33%
Recovered with lasting effects
5 12%
Still unwell when reported
5 12%
Died
1 2.3%
Euthanised
5 12%
Not known
13 30%

Problems reported at the same time

Age of the animals

Under 1 year
6
1–3 years
17
4–7 years
10
8–11 years
7
12+ years
2

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 urinary retention in dogs?
43 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).

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