Leucocytosis after Levothyroxine in dogs

The FDA has received 47 reports of leucocytosis in dogs after Levothyroxine. That is 1.6% of all reports for this medicine, compared with 1.0% across reports for all dog medicines.

47Reports

81%Marked serious

8.5%Recovered

51%Died or euthanised

41 daysTypical onset

How soon it started

Same day

5 14%

1–2 days

3 8.1%

3–7 days

5 14%

1–4 weeks

5 14%

Over a month

19 51%

How the animals did

Recovered

3 6.4%

Recovered with lasting effects

1 2.1%

Still unwell when reported

15 32%

Died

9 19%

Euthanised

15 32%

Not known

4 8.5%

Problems reported at the same time

30 64%

24 51%

21 45%

21 45%

20 43%

20 43%

19 40%

18 38%

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 leucocytosis in dogs?: 47 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 41 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).

Leucocytosis with similar medicines

Leucocytosis after Trilostane (Vetoryl) 190 reports · 1.6% of its reports
Leucocytosis after Insulin 78 reports · 1.1% of its reports
Leucocytosis after Phenylpropanolamine (Proin) 47 reports · 1.1% of its reports

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