Didn't prevent heartworm after Ivermectin (Heartgard) in cats

45 reports to the FDA describe didn't prevent heartworm in cats given Ivermectin. That is 4.7% of all reports for this medicine, compared with 0.3% across reports for all cat medicines, so it is reported unusually often with this medicine.

45Reports

8.9%Marked serious

0.0%Recovered

2.2%Died or euthanised

–Typical onset

How the animals did

Died

1 2.2%

Not known

44 98%

Problems reported at the same time

Vomiting

2 4.4%

Diarrhea

2 4.4%

Cardiac disorder

2 4.4%

Fever

1 2.2%

Muscle stiffness

1 2.2%

Locomotor disturbance

1 2.2%

Death

1 2.2%

Digestive tract disorder

1 2.2%

Age of the animals

Under 1 year

1–3 years

4–7 years

8–11 years

12+ years

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 didn't prevent heartworm in cats?: 45 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).

Didn't prevent heartworm with similar medicines

Didn't prevent heartworm after Selamectin (Revolution) 285 reports · 1.3% of its reports

All reported side effects of Ivermectin in cats · Medicines most reported with didn't prevent heartworm