Swelling after Methimazole in cats

The FDA has received 65 reports of swelling in cats after Methimazole. That is 3.6% of all reports for this medicine, compared with 1.9% across reports for all cat medicines, so it is reported unusually often with this medicine.

65Reports

72%Marked serious

29%Recovered

22%Died or euthanised

15 daysTypical onset

How soon it started

Same day

8 15%

1–2 days

5 9.1%

3–7 days

4 7.3%

1–4 weeks

23 42%

Over a month

15 27%

How the animals did

Recovered

19 29%

Still unwell when reported

15 23%

Died

6 9.2%

Euthanised

8 12%

Not known

17 26%

Problems reported at the same time

19 29%

19 29%

19 29%

16 25%

14 22%

9 14%

7 11%

7 11%

Age of the animals

Under 1 year

1–3 years

4–7 years

8–11 years

12+ years

About this medicine

Methimazole treats an overactive thyroid in cats.

Questions owners ask

Can Methimazole cause swelling in cats?: 65 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 15 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).

Swelling with similar medicines

Swelling after Insulin 32 reports · 0.9% of its reports

All reported side effects of Methimazole in cats · Medicines most reported with swelling