Did you miss a dose of heartworm prevention medicine?
Do not panic. Here is what to do if you missed a dose.
If you have missed a dose of heartworm prevention medicine, there are several things you need to take into consideration before starting your pet back on preventatives.
However, if your pet has never been on heartworm prevention, it is important to get started right away. Heartworm disease has been reported in all 50 states year-round. Monthly preventatives can help your pet avoid this potentially deadly disease.
Why Is It Important to Never Miss a Heartworm Dose?
The American Heartworm Society recommends year-round protection without missing a dose. A missed dose leaves your pet exposed to infection, which can happen even in winter. Making monthly medication part of your pet’s routine makes it easier to remember.
It may help to remember that:
- Heartworm disease is deadly but preventable
- Heartworm disease has been documented in all 50 states throughout the year
- Infection can cause heart and lung damage in dogs and cats
- Symptoms may include exercise intolerance, coughing, heart failure, vomiting, lethargy, abdominal swelling, and, in severe cases, sudden death
Do I Need to Test My Pet Immediately?
It is not necessary to test your pet immediately if you have missed one month of heartworm medication. It takes at least six months for a pet to test positive after infection from a mosquito carrying heartworms.
This means that even if your pet became infected during the missed dose window, results would not show as positive until six months later.
What If the Dose Is Only a Few Days Late?
Most monthly heartworm medications provide a safety buffer of about 15 days. If you are only a week or two late, your pet is likely still protected.
In this case, simply resume giving your pet their medication and continue on your regular schedule. You can browse monthly options at 1800petmeds.com.
What If My Pet Missed a Full Month?
If your pet has missed a full month, give the missed dose as soon as possible and restart the monthly schedule.
At your pet’s next annual or semi-annual exam, a routine heartworm test is recommended along with a full wellness check.
While it is best to stay consistent, missing a single dose occasionally is not typically harmful in isolated situations.
Why Consistency Matters
Even though missing a dose once may not cause harm, irregular use of heartworm medication is not recommended. Inconsistent use of parasite prevention may contribute to resistance.
It is also difficult to predict when heartworm transmission begins or ends, since mosquitoes can be active even during cooler months in some areas.
Staying consistent with prevention is one of the best ways to protect your pet. Learn more about prevention products at 1800petmeds.
Being a responsible pet parent means providing consistent care, proper nutrition, and protection from preventable diseases like heartworm.


