Monocytosis after Ivermectin + Pyrantel (Heartgard Plus) in dogs

The FDA has received 185 reports of monocytosis 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.

185Reports

69%Marked serious

15%Recovered

20%Died or euthanised

7 daysTypical onset

How soon it started

Same day

27 25%

1–2 days

17 16%

3–7 days

13 12%

1–4 weeks

23 21%

Over a month

28 26%

How the animals did

Recovered

19 10%

Recovered with lasting effects

8 4.3%

Still unwell when reported

43 23%

Died

16 8.6%

Euthanised

21 11%

Not known

78 42%

Problems reported at the same time

105 57%

100 54%

90 49%

85 46%

80 43%

69 37%

51 28%

48 26%

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 monocytosis in dogs?: 185 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 7 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).

Monocytosis with similar medicines

Monocytosis after Milbemycin Oxime + Spinosad (Trifexis) 96 reports · 0.1% of its reports
Monocytosis after Moxidectin (ProHeart 6) 177 reports · 0.3% of its reports
Monocytosis after Milbemycin Oxime + Praziquantel (Interceptor Plus) 76 reports · 0.2% of its reports
Monocytosis after Milbemycin Oxime (Interceptor) 29 reports · 0.1% of its reports
Monocytosis after Selamectin (Revolution) 36 reports · 0.1% of its reports
Monocytosis after Ivermectin (Heartgard) 31 reports · 0.3% of its reports

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