Decreased packed cell volume (pcv) after Methimazole in cats

28 reports to the FDA describe decreased packed cell volume (pcv) in cats given Methimazole. That is 1.6% of all reports for this medicine, compared with 0.3% across reports for all cat medicines, so it is reported unusually often with this medicine.

28Reports

68%Marked serious

7.1%Recovered

11%Died or euthanised

22 daysTypical onset

How soon it started

Same day

1 4.2%

1–2 days

0 0.0%

3–7 days

0 0.0%

1–4 weeks

15 63%

Over a month

8 33%

How the animals did

Recovered

2 7.1%

Still unwell when reported

5 18%

Died

1 3.6%

Euthanised

2 7.1%

Not known

18 64%

Problems reported at the same time

13 46%

12 43%

11 39%

8 29%

8 29%

7 25%

6 21%

Decreased haemoglobin

6 21%

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 decreased packed cell volume (pcv) in cats?: 28 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 22 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).

Decreased packed cell volume (pcv) with similar medicines

Decreased packed cell volume (pcv) after Velagliflozin (Senvelgo) 38 reports · 0.8% of its reports

All reported side effects of Methimazole in cats · Medicines most reported with decreased packed cell volume (pcv)