Elevated thyroxine (t4) after Levothyroxine in dogs

The FDA has received 105 reports of elevated thyroxine (t4) in dogs after Levothyroxine. That is 3.5% of all reports for this medicine, compared with 0.0% across reports for all dog medicines, so it is reported unusually often with this medicine.

105Reports

66%Marked serious

31%Recovered

2.9%Died or euthanised

45 daysTypical onset

How soon it started

Same day

4 6.1%

1–2 days

3 4.5%

3–7 days

6 9.1%

1–4 weeks

16 24%

Over a month

37 56%

How the animals did

Recovered

32 30%

Recovered with lasting effects

1 1.0%

Still unwell when reported

22 21%

Died

1 1.0%

Euthanised

2 1.9%

Not known

47 45%

Problems reported at the same time

38 36%

24 23%

23 22%

15 14%

14 13%

13 12%

13 12%

12 11%

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 elevated thyroxine (t4) in dogs?: 105 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 45 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).

Elevated thyroxine (t4) with similar medicines

Elevated thyroxine (t4) after Trilostane (Vetoryl) 29 reports · 0.2% of its reports

All reported side effects of Levothyroxine in dogs · Medicines most reported with elevated thyroxine (t4)