Didn't prevent heartworm after Levothyroxine in dogs

The FDA has received 29 reports of didn't prevent heartworm in dogs after Levothyroxine. That is 1.0% of all reports for this medicine, compared with 13% across reports for all dog medicines, so it is reported less often than average with this medicine.

29Reports

41%Marked serious

6.9%Recovered

0.0%Died or euthanised

–Typical onset

How the animals did

Recovered with lasting effects

2 6.9%

Still unwell when reported

10 34%

Not known

17 59%

Problems reported at the same time

Didn't work as expected

6 21%

Drug dose omission

4 14%

4 14%

3 10%

2 6.9%

2 6.9%

2 6.9%

2 6.9%

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 didn't prevent heartworm in dogs?: 29 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.
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).

Didn't prevent heartworm with similar medicines

Didn't prevent heartworm after Phenylpropanolamine (Proin) 23 reports · 0.6% of its reports

All reported side effects of Levothyroxine in dogs · Medicines most reported with didn't prevent heartworm