Allergic reaction after Ivermectin (Heartgard) in horses

The FDA has received 35 reports of allergic reaction in horses after Ivermectin. That is 5.1% of all reports for this medicine, compared with 7.5% across reports for all horse medicines.

35Reports
8.6%Marked serious
14%Recovered
14%Died or euthanised
–Typical onset
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How the animals did

Recovered
4 11%
Recovered with lasting effects
1 2.9%
Still unwell when reported
2 5.7%
Died
4 11%
Euthanised
1 2.9%
Not known
23 66%

Problems reported at the same time

14 40%
5 14%
4 11%
3 8.6%
Colic
3 8.6%
Collapse
2 5.7%

Age of the animals

Under 1 year
0
1–3 years
1
4–7 years
8
8–11 years
6
12+ years
11

About this medicine

Ivermectin prevents heartworm disease (monthly).

Products with this ingredient include Heartgard. 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 Ivermectin cause allergic reaction in horses?
35 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.
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).

Allergic reaction with similar medicines

All reported side effects of Ivermectin in horses · Medicines most reported with allergic reaction