Milbemycin Oxime + Spinosad (Trifexis) side effects in cats
300 reports sent to the FDA between 2011 and 2025 involve Milbemycin Oxime + Spinosad in cats. The most reported problems were vomiting, accidental exposure, lethargy. 12% were marked serious.
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.
Most reported side effects
Share = percentage of this medicine's reports that mention the problem. One report can list several problems.
Reports that it didn't work
Some reports are about the medicine not working (for example a cat still getting fleas or heartworm), not about a side effect.
How soon problems started
Time from the first dose to the first sign, where both dates were reported (268 reports).
How the animals did
Breeds named most often
Popular breeds appear more often because there are more of them.
- Domestic Shorthair 175 reports
- Domestic Longhair 22 reports
- Domestic Mediumhair 18 reports
- Domestic 17 reports
- Siamese 9 reports
- Ragdoll 3 reports
- Maine Coon 2 reports
- Russian 2 reports
- American Shorthair 2 reports
- Bengal 1 reports