Blood problems after Selamectin (Revolution) in cats

319 reports to the FDA describe blood problems in cats given Selamectin. That is 1.5% of all reports for this medicine, compared with 1.9% across reports for all cat medicines.

319Reports
29%Marked serious
4.1%Recovered
30%Died or euthanised
3 daysTypical onset
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How soon it started

Same day
31 26%
1–2 days
25 21%
3–7 days
22 18%
1–4 weeks
20 17%
Over a month
21 18%

How the animals did

Recovered
12 3.8%
Recovered with lasting effects
1 0.3%
Still unwell when reported
76 24%
Died
74 23%
Euthanised
22 6.9%
Not known
134 42%

Problems reported at the same time

Age of the animals

Under 1 year
75
1–3 years
72
4–7 years
54
8–11 years
54
12+ years
51

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 blood problems in cats?
319 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 3 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).

Blood problems with similar medicines

All reported side effects of Selamectin in cats · Medicines most reported with blood problems