Lymphopenia after Methimazole in cats

24 reports to the FDA describe lymphopenia in cats given Methimazole. That is 1.3% of all reports for this medicine, compared with 0.4% across reports for all cat medicines, so it is reported unusually often with this medicine.

24Reports

75%Marked serious

4.2%Recovered

21%Died or euthanised

24 daysTypical onset

How soon it started

Same day

4 20%

1–2 days

2 10%

3–7 days

1 5.0%

1–4 weeks

7 35%

Over a month

6 30%

How the animals did

Recovered with lasting effects

1 4.2%

Still unwell when reported

7 29%

Euthanised

5 21%

Not known

11 46%

Problems reported at the same time

14 58%

13 54%

11 46%

10 42%

9 38%

9 38%

8 33%

7 29%

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 lymphopenia in cats?: 24 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 24 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).

Lymphopenia with similar medicines

Lymphopenia after Velagliflozin (Senvelgo) 35 reports · 0.7% of its reports

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