Didn't stop worms after Moxidectin + Praziquantel in horses

The FDA has received 48 reports of didn't stop worms in horses after Moxidectin + Praziquantel. That is 13% of all reports for this medicine, compared with 2.1% across reports for all horse medicines, so it is reported unusually often with this medicine.

48Reports
10%Marked serious
15%Recovered
8.3%Died or euthanised
62 daysTypical onset
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How soon it started

Same day
0 0.0%
1–2 days
0 0.0%
3–7 days
0 0.0%
1–4 weeks
6 24%
Over a month
19 76%

How the animals did

Recovered
7 15%
Still unwell when reported
7 15%
Died
1 2.1%
Euthanised
3 6.3%
Not known
30 63%

Problems reported at the same time

Didn't work as expected
14 29%
Death
5 10%
Abdominal pain
2 4.2%
Intussusception
2 4.2%
Overdose
2 4.2%
Necropsy performed
2 4.2%
Digestive tract stenosis and obstruction
1 2.1%
Digestive tract disorder
1 2.1%

Age of the animals

Under 1 year
3
1–3 years
9
4–7 years
7
8–11 years
7
12+ years
15

About this medicine

Moxidectin prevents heartworm disease (monthly topical, or a 6- or 12-month injection for dogs). Praziquantel treats tapeworms.

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 Moxidectin + Praziquantel cause didn't stop worms in horses?
48 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 62 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

All reported side effects of Moxidectin + Praziquantel in horses · Medicines most reported with didn't stop worms