Abnormal cytology after Levothyroxine in dogs

35 reports to the FDA describe abnormal cytology in dogs given Levothyroxine. That is 1.2% 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.

35Reports

80%Marked serious

5.7%Recovered

14%Died or euthanised

67 daysTypical onset

How soon it started

Same day

0 0.0%

1–2 days

2 8.0%

3–7 days

3 12%

1–4 weeks

4 16%

Over a month

16 64%

How the animals did

Recovered

2 5.7%

Still unwell when reported

22 63%

Euthanised

5 14%

Not known

6 17%

Problems reported at the same time

Didn't work as expected

11 31%

9 26%

8 23%

8 23%

7 20%

7 20%

5 14%

Abnormal radiograph finding

5 14%

Age of the animals

Under 1 year

1–3 years

4–7 years

8–11 years

12+ years

About this medicine

Levothyroxine treats an underactive thyroid.

Questions owners ask

Can Levothyroxine cause abnormal cytology in dogs?: 35 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 67 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 Trilostane (Vetoryl) 44 reports · 0.4% of its reports

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