Hyperphosphataemia after Levothyroxine in dogs

41 reports to the FDA describe hyperphosphataemia in dogs given Levothyroxine. That is 1.4% of all reports for this medicine, compared with 0.6% across reports for all dog medicines, so it is reported unusually often with this medicine.

41Reports

80%Marked serious

17%Recovered

37%Died or euthanised

57 daysTypical onset

How soon it started

Same day

2 7.7%

1–2 days

1 3.8%

3–7 days

1 3.8%

1–4 weeks

5 19%

Over a month

17 65%

How the animals did

Recovered

1 2.4%

Recovered with lasting effects

6 15%

Still unwell when reported

12 29%

Died

4 9.8%

Euthanised

11 27%

Not known

7 17%

Problems reported at the same time

33 80%

29 71%

25 61%

15 37%

15 37%

15 37%

12 29%

11 27%

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 hyperphosphataemia in dogs?: 41 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 57 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).

Hyperphosphataemia with similar medicines

Hyperphosphataemia after Trilostane (Vetoryl) 373 reports · 3.1% of its reports
Hyperphosphataemia after Insulin 48 reports · 0.7% of its reports
Hyperphosphataemia after Phenylpropanolamine (Proin) 53 reports · 1.3% of its reports

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