Mast cell tumour after Milbemycin Oxime + Praziquantel (Interceptor Plus) in dogs

The FDA has received 26 reports of mast cell tumour in dogs after Milbemycin Oxime + Praziquantel. That is 0.1% of all reports for this medicine, compared with 0.0% across reports for all dog medicines, so it is reported unusually often with this medicine.

26Reports
96%Marked serious
7.7%Recovered
12%Died or euthanised
178 daysTypical onset
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How soon it started

Same day
1 8.3%
1–2 days
0 0.0%
3–7 days
0 0.0%
1–4 weeks
3 25%
Over a month
8 67%

How the animals did

Recovered
2 7.7%
Still unwell when reported
8 31%
Died
2 7.7%
Euthanised
1 3.8%
Not known
13 50%

Problems reported at the same time

Age of the animals

Under 1 year
0
1–3 years
2
4–7 years
11
8–11 years
5
12+ years
3

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 mast cell tumour in dogs?
26 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 178 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).

All reported side effects of Milbemycin Oxime + Praziquantel in dogs · Medicines most reported with mast cell tumour