Hypothyroidism after Moxidectin (ProHeart 6) in dogs

The FDA has received 67 reports of hypothyroidism in dogs after Moxidectin. That is 0.1% of all reports for this medicine, compared with 0.2% across reports for all dog medicines.

67Reports

21%Marked serious

1.5%Recovered

37%Died or euthanised

61 daysTypical onset

How soon it started

Same day

1 6.3%

1–2 days

1 6.3%

3–7 days

2 13%

1–4 weeks

2 13%

Over a month

10 63%

How the animals did

Recovered

1 1.5%

Still unwell when reported

9 13%

Died

19 28%

Euthanised

6 9.0%

Not known

32 48%

Problems reported at the same time

29 43%

25 37%

25 37%

19 28%

17 25%

16 24%

15 22%

14 21%

Age of the animals

Under 1 year

1–3 years

4–7 years

8–11 years

12+ years

About this medicine

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

Products with this ingredient include ProHeart 6, ProHeart 12. 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 Moxidectin cause hypothyroidism in dogs?: 67 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 61 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).

Hypothyroidism with similar medicines

Hypothyroidism after Ivermectin + Pyrantel (Heartgard Plus) 46 reports · 0.0% of its reports
Hypothyroidism after Milbemycin Oxime + Spinosad (Trifexis) 193 reports · 0.1% of its reports
Hypothyroidism after Milbemycin Oxime + Praziquantel (Interceptor Plus) 39 reports · 0.1% of its reports
Hypothyroidism after Milbemycin Oxime (Interceptor) 35 reports · 0.1% of its reports
Hypothyroidism after Selamectin (Revolution) 32 reports · 0.1% of its reports

All reported side effects of Moxidectin in dogs · Medicines most reported with hypothyroidism