Didn't prevent heartworm after Milbemycin Oxime + Praziquantel (Interceptor Plus) in dogs

The FDA has received 8,433 reports of didn't prevent heartworm in dogs after Milbemycin Oxime + Praziquantel. That is 27% of all reports for this medicine, compared with 13% across reports for all dog medicines, so it is reported unusually often with this medicine.

8,433Reports

6.2%Marked serious

0.4%Recovered

0.5%Died or euthanised

280 daysTypical onset

How soon it started

Same day

41 1.6%

1–2 days

7 0.3%

3–7 days

15 0.6%

1–4 weeks

92 3.7%

Over a month

2,357 94%

How the animals did

Recovered

26 0.3%

Recovered with lasting effects

11 0.1%

Still unwell when reported

501 5.9%

Died

23 0.3%

Euthanised

18 0.2%

Not known

7,854 93%

Problems reported at the same time

339 4.0%

327 3.9%

152 1.8%

132 1.6%

110 1.3%

101 1.2%

81 1.0%

77 0.9%

Age of the animals

Under 1 year

262

1–3 years

4,855

4–7 years

2,148

8–11 years

871

12+ years

182

About this medicine

Milbemycin Oxime prevents heartworm and controls some intestinal worms (monthly). Praziquantel treats tapeworms.

Products with this combination include Interceptor 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 Milbemycin Oxime + Praziquantel cause didn't prevent heartworm in dogs?: 8,433 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 280 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).

Didn't prevent heartworm with similar medicines

Didn't prevent heartworm after Ivermectin + Pyrantel (Heartgard Plus) 57,581 reports · 39% of its reports
Didn't prevent heartworm after Milbemycin Oxime + Spinosad (Trifexis) 10,801 reports · 8.3% of its reports
Didn't prevent heartworm after Moxidectin (ProHeart 6) 11,529 reports · 23% of its reports
Didn't prevent heartworm after Milbemycin Oxime (Interceptor) 13,118 reports · 44% of its reports
Didn't prevent heartworm after Selamectin (Revolution) 8,789 reports · 30% of its reports
Didn't prevent heartworm after Ivermectin (Heartgard) 3,385 reports · 28% of its reports
Didn't prevent heartworm after Ivermectin + Praziquantel + Pyrantel (Iverhart Max) 1,879 reports · 22% of its reports
Didn't prevent heartworm after Moxidectin + Pyrantel + Sarolaner (Simparica Trio) 319 reports · 28% of its reports

All reported side effects of Milbemycin Oxime + Praziquantel in dogs · Medicines most reported with didn't prevent heartworm