Underdose after Ivermectin + Pyrantel (Heartgard Plus) in dogs

The FDA has received 1,810 reports of underdose in dogs after Ivermectin + Pyrantel. That is 1.2% of all reports for this medicine, compared with 1.0% across reports for all dog medicines.

1,810Reports

52%Marked serious

32%Recovered

1.2%Died or euthanised

120 daysTypical onset

How soon it started

Same day

36 5.7%

1–2 days

35 5.5%

3–7 days

32 5.1%

1–4 weeks

163 26%

Over a month

366 58%

How the animals did

Recovered

118 6.5%

Recovered with lasting effects

470 26%

Still unwell when reported

236 13%

Died

10 0.6%

Euthanised

12 0.7%

Not known

964 53%

Problems reported at the same time

Didn't prevent heartworm

1,052 58%

Didn't stop worms

353 20%

Didn't work as expected

330 18%

Cardiac disorder

278 15%

Digestive tract disorder

241 13%

Weight gain

213 12%

Vomiting

96 5.3%

Diarrhea

78 4.3%

Age of the animals

Under 1 year

166

1–3 years

919

4–7 years

488

8–11 years

187

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 underdose in dogs?: 1,810 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 120 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).

Underdose with similar medicines

Underdose after Milbemycin Oxime + Spinosad (Trifexis) 750 reports · 0.6% of its reports
Underdose after Moxidectin (ProHeart 6) 180 reports · 0.4% of its reports
Underdose after Milbemycin Oxime + Praziquantel (Interceptor Plus) 153 reports · 0.5% of its reports
Underdose after Milbemycin Oxime (Interceptor) 118 reports · 0.4% of its reports
Underdose after Selamectin (Revolution) 179 reports · 0.6% of its reports
Underdose after Ivermectin (Heartgard) 99 reports · 0.8% of its reports
Underdose after Ivermectin + Praziquantel + Pyrantel (Iverhart Max) 98 reports · 1.1% of its reports

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