Abnormal cytology after Moxidectin (ProHeart 6) in dogs

The FDA has received 234 reports of abnormal cytology in dogs after Moxidectin. That is 0.5% of all reports for this medicine, compared with 0.2% across reports for all dog medicines, so it is reported unusually often with this medicine.

234Reports

56%Marked serious

11%Recovered

5.6%Died or euthanised

17 daysTypical onset

How soon it started

Same day

31 15%

1–2 days

17 8.1%

3–7 days

29 14%

1–4 weeks

70 33%

Over a month

64 30%

How the animals did

Recovered

26 11%

Still unwell when reported

186 79%

Died

3 1.3%

Euthanised

10 4.3%

Not known

9 3.8%

Problems reported at the same time

Injection site reaction

141 60%

69 29%

29 12%

28 12%

26 11%

14 6.0%

13 5.6%

13 5.6%

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 abnormal cytology in dogs?: 234 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 17 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).

Abnormal cytology with similar medicines

Abnormal cytology after Ivermectin + Pyrantel (Heartgard Plus) 73 reports · 0.0% of its reports
Abnormal cytology after Milbemycin Oxime + Spinosad (Trifexis) 31 reports · 0.0% of its reports
Abnormal cytology after Milbemycin Oxime + Praziquantel (Interceptor Plus) 37 reports · 0.1% of its reports
Abnormal cytology after Ivermectin (Heartgard) 22 reports · 0.2% of its reports

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