Decreased red blood cell count after Ivermectin + Pyrantel (Heartgard Plus) in dogs

The FDA has received 92 reports of decreased red blood cell count in dogs after Ivermectin + Pyrantel. That is 0.1% of all reports for this medicine, compared with 0.1% across reports for all dog medicines, so it is reported less often than average with this medicine.

92Reports

76%Marked serious

13%Recovered

20%Died or euthanised

8 daysTypical onset

How soon it started

Same day

5 9.8%

1–2 days

9 18%

3–7 days

9 18%

1–4 weeks

15 29%

Over a month

13 25%

How the animals did

Recovered

10 11%

Recovered with lasting effects

2 2.2%

Still unwell when reported

33 36%

Died

7 7.6%

Euthanised

11 12%

Not known

29 32%

Problems reported at the same time

39 42%

37 40%

37 40%

36 39%

Decreased haemoglobin

34 37%

Decreased packed cell volume (pcv)

29 32%

Leucocytosis

28 30%

Neutrophilia

26 28%

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 decreased red blood cell count in dogs?: 92 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 8 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).

Decreased red blood cell count with similar medicines

Decreased red blood cell count after Milbemycin Oxime + Spinosad (Trifexis) 57 reports · 0.0% of its reports
Decreased red blood cell count after Moxidectin (ProHeart 6) 51 reports · 0.1% of its reports
Decreased red blood cell count after Milbemycin Oxime + Praziquantel (Interceptor Plus) 39 reports · 0.1% of its reports
Decreased red blood cell count after Ivermectin (Heartgard) 20 reports · 0.2% of its reports

All reported side effects of Ivermectin + Pyrantel in dogs · Medicines most reported with decreased red blood cell count