Didn't stop fleas after Selamectin (Revolution) in cats

2,397 reports to the FDA describe didn't stop fleas in cats given Selamectin. That is 11% of all reports for this medicine, compared with 8.4% across reports for all cat medicines.

2,397Reports
4.3%Marked serious
1.5%Recovered
1.3%Died or euthanised
21 daysTypical onset
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How soon it started

Same day
192 21%
1–2 days
75 8.1%
3–7 days
76 8.2%
1–4 weeks
164 18%
Over a month
416 45%

How the animals did

Recovered
35 1.5%
Recovered with lasting effects
1 0.0%
Still unwell when reported
448 19%
Died
25 1.0%
Euthanised
7 0.3%
Not known
1,881 78%

Problems reported at the same time

Age of the animals

Under 1 year
261
1–3 years
466
4–7 years
402
8–11 years
269
12+ years
255

About this medicine

Selamectin prevents heartworm and treats fleas, ear mites and some worms (spot-on).

Products with this ingredient include Revolution. 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 Selamectin cause didn't stop fleas in cats?
2,397 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 21 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).

Didn't stop fleas with similar medicines

All reported side effects of Selamectin in cats · Medicines most reported with didn't stop fleas