Lethargy after Milbemycin Oxime + Praziquantel (Interceptor Plus) in dogs

The FDA has received 2,407 reports of lethargy in dogs after Milbemycin Oxime + Praziquantel. That is 7.6% of all reports for this medicine, compared with 11% across reports for all dog medicines.

2,407Reports

23%Marked serious

39%Recovered

5.1%Died or euthanised

1 daysTypical onset

How soon it started

Same day

795 42%

1–2 days

291 15%

3–7 days

109 5.7%

1–4 weeks

125 6.6%

Over a month

584 31%

How the animals did

Recovered

929 39%

Recovered with lasting effects

7 0.3%

Still unwell when reported

746 31%

Died

53 2.2%

Euthanised

70 2.9%

Not known

602 25%

Problems reported at the same time

968 40%

813 34%

539 22%

252 10%

236 9.8%

193 8.0%

189 7.9%

156 6.5%

Age of the animals

Under 1 year

465

1–3 years

687

4–7 years

552

8–11 years

426

12+ years

210

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 lethargy in dogs?: 2,407 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 1 day 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 (Interceptor) 2,528 reports · 8.5% 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 + Praziquantel in dogs · Medicines most reported with lethargy