Didn't prevent heartworm after Doxycycline in dogs

The FDA has received 1,398 reports of didn't prevent heartworm in dogs after Doxycycline. That is 35% of all reports for this medicine, compared with 13% across reports for all dog medicines, so it is reported unusually often with this medicine.

1,398Reports
63%Marked serious
3.9%Recovered
1.5%Died or euthanised
212 daysTypical onset
SponsoredWorried about your pet? Ask a veterinarian online, 24/7

How soon it started

Same day
14 1.6%
1–2 days
0 0.0%
3–7 days
3 0.3%
1–4 weeks
31 3.6%
Over a month
812 94%

How the animals did

Recovered
49 3.5%
Recovered with lasting effects
6 0.4%
Still unwell when reported
902 65%
Died
10 0.7%
Euthanised
11 0.8%
Not known
420 30%

Problems reported at the same time

Didn't work as expected
79 5.7%
Vomiting
51 3.6%
Medication error
48 3.4%
Intentional misuse
42 3.0%
Cough
33 2.4%
Liver problems
33 2.4%
Weight gain
32 2.3%
Lethargy
32 2.3%

Age of the animals

Under 1 year
7
1–3 years
699
4–7 years
470
8–11 years
160
12+ years
21

About this medicine

Doxycycline treats bacterial and tick-borne infections.

Questions owners ask

Can Doxycycline cause didn't prevent heartworm in dogs?
1,398 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 212 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).

Didn't prevent heartworm with similar medicines

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