Fever after Levothyroxine in dogs

The FDA has received 50 reports of fever in dogs after Levothyroxine. That is 1.7% of all reports for this medicine, compared with 1.4% across reports for all dog medicines.

50Reports

78%Marked serious

12%Recovered

42%Died or euthanised

9 daysTypical onset

How soon it started

Same day

5 14%

1–2 days

5 14%

3–7 days

8 22%

1–4 weeks

6 16%

Over a month

13 35%

How the animals did

Recovered

5 10%

Recovered with lasting effects

1 2.0%

Still unwell when reported

13 26%

Died

5 10%

Euthanised

16 32%

Not known

10 20%

Problems reported at the same time

23 46%

23 46%

21 42%

15 30%

14 28%

14 28%

10 20%

8 16%

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 fever in dogs?: 50 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 9 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).

Fever with similar medicines

Fever after Trilostane (Vetoryl) 81 reports · 0.7% of its reports
Fever after Insulin 53 reports · 0.7% of its reports
Fever after Phenylpropanolamine (Proin) 94 reports · 2.3% of its reports

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