Didn't stop worms after Milbemycin Oxime (Interceptor) in dogs

The FDA has received 4,308 reports of didn't stop worms in dogs after Milbemycin Oxime. That is 14% of all reports for this medicine, compared with 8.4% across reports for all dog medicines, so it is reported unusually often with this medicine.

4,308Reports

1.7%Marked serious

3.1%Recovered

2.6%Died or euthanised

33 daysTypical onset

How soon it started

Same day

7 2.2%

1–2 days

11 3.5%

3–7 days

20 6.3%

1–4 weeks

106 33%

Over a month

173 55%

How the animals did

Recovered

125 2.9%

Recovered with lasting effects

7 0.2%

Still unwell when reported

195 4.5%

Died

107 2.5%

Euthanised

6 0.1%

Not known

3,868 90%

Problems reported at the same time

Diarrhea

986 23%

Didn't work as expected

605 14%

335 7.8%

189 4.4%

134 3.1%

120 2.8%

109 2.5%

101 2.3%

Age of the animals

Under 1 year

469

1–3 years

1,495

4–7 years

1,066

8–11 years

824

12+ years

343

About this medicine

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

Products with this ingredient include Interceptor. 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 cause didn't stop worms in dogs?: 4,308 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 33 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 stop worms with similar medicines

Didn't stop worms after Ivermectin + Pyrantel (Heartgard Plus) 32,467 reports · 22% of its reports
Didn't stop worms after Milbemycin Oxime + Spinosad (Trifexis) 4,483 reports · 3.5% of its reports
Didn't stop worms after Moxidectin (ProHeart 6) 9,537 reports · 19% of its reports
Didn't stop worms after Milbemycin Oxime + Praziquantel (Interceptor Plus) 6,097 reports · 19% of its reports
Didn't stop worms after Selamectin (Revolution) 2,317 reports · 7.9% of its reports
Didn't stop worms after Ivermectin (Heartgard) 254 reports · 2.1% of its reports
Didn't stop worms after Ivermectin + Praziquantel + Pyrantel (Iverhart Max) 1,299 reports · 15% of its reports
Didn't stop worms after Moxidectin + Pyrantel + Sarolaner (Simparica Trio) 132 reports · 11% of its reports

All reported side effects of Milbemycin Oxime in dogs · Medicines most reported with didn't stop worms