Lymphopenia after Ivermectin + Pyrantel (Heartgard Plus) in dogs

The FDA has received 146 reports of lymphopenia in dogs after Ivermectin + Pyrantel. That is 0.1% of all reports for this medicine, compared with 0.3% across reports for all dog medicines, so it is reported less often than average with this medicine.

146Reports

75%Marked serious

19%Recovered

20%Died or euthanised

9 daysTypical onset

How soon it started

Same day

15 20%

1–2 days

8 11%

3–7 days

10 14%

1–4 weeks

18 24%

Over a month

23 31%

How the animals did

Recovered

22 15%

Recovered with lasting effects

6 4.1%

Still unwell when reported

35 24%

Died

11 7.5%

Euthanised

18 12%

Not known

54 37%

Problems reported at the same time

81 55%

69 47%

56 38%

53 36%

40 27%

38 26%

34 23%

33 23%

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). Pyrantel treats roundworms and hookworms.

Products with this combination include Heartgard Plus, Tri-Heart Plus, Iverhart Plus. 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 + Pyrantel cause lymphopenia in dogs?: 146 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 9 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).

Lymphopenia with similar medicines

Lymphopenia after Milbemycin Oxime + Spinosad (Trifexis) 179 reports · 0.1% of its reports
Lymphopenia after Moxidectin (ProHeart 6) 139 reports · 0.3% of its reports
Lymphopenia after Milbemycin Oxime + Praziquantel (Interceptor Plus) 48 reports · 0.2% of its reports
Lymphopenia after Milbemycin Oxime (Interceptor) 35 reports · 0.1% of its reports
Lymphopenia after Selamectin (Revolution) 26 reports · 0.1% of its reports
Lymphopenia after Ivermectin (Heartgard) 36 reports · 0.3% of its reports

All reported side effects of Ivermectin + Pyrantel in dogs · Medicines most reported with lymphopenia