Lethargy after Milbemycin Oxime (Interceptor) in dogs

2,528 reports to the FDA describe lethargy in dogs given Milbemycin Oxime. That is 8.5% of all reports for this medicine, compared with 11% across reports for all dog medicines.

2,528Reports

12%Marked serious

13%Recovered

8.0%Died or euthanised

2 daysTypical onset

How soon it started

Same day

168 34%

1–2 days

87 18%

3–7 days

28 5.6%

1–4 weeks

51 10%

Over a month

163 33%

How the animals did

Recovered

320 13%

Recovered with lasting effects

14 0.6%

Still unwell when reported

215 8.5%

Died

169 6.7%

Euthanised

32 1.3%

Not known

1,778 70%

Problems reported at the same time

888 35%

800 32%

508 20%

258 10%

237 9.4%

204 8.1%

187 7.4%

166 6.6%

Age of the animals

Under 1 year

529

1–3 years

784

4–7 years

616

8–11 years

381

12+ years

180

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 lethargy in dogs?: 2,528 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 2 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).

Lethargy with similar medicines

Lethargy after Ivermectin + Pyrantel (Heartgard Plus) 7,391 reports · 5.0% of its reports
Lethargy after Milbemycin Oxime + Spinosad (Trifexis) 19,835 reports · 15% of its reports
Lethargy after Moxidectin (ProHeart 6) 6,640 reports · 13% of its reports
Lethargy after Milbemycin Oxime + Praziquantel (Interceptor Plus) 2,407 reports · 7.6% of its reports
Lethargy after Selamectin (Revolution) 2,964 reports · 10% of its reports
Lethargy after Ivermectin (Heartgard) 1,488 reports · 12% of its reports
Lethargy after Ivermectin + Praziquantel + Pyrantel (Iverhart Max) 969 reports · 11% of its reports
Lethargy after Moxidectin + Pyrantel + Sarolaner (Simparica Trio) 135 reports · 12% of its reports
Lethargy after Ivermectin + Praziquantel 35 reports · 17% of its reports
Lethargy after Moxidectin + Praziquantel 21 reports · 28% of its reports

All reported side effects of Milbemycin Oxime in dogs · Medicines most reported with lethargy