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What to Do If You Missed a Heartworm Dose

We all have the best of intentions when it comes to looking after our pets, but sometimes things don’t go as planned. Whether you thought mosquito season had finished for the year or you simply forgot, here’s what you should do if you missed giving your dog or cat their regular heartworm medication.

Why regular dosing is important

Knowing how heartworm preventatives work can help us understand just why regular dosing is important, and how missing a dose can impact the effectiveness of the medication. Despite the name, preventatives can’t actually stop heartworm larvae from entering an animal’s blood stream. What the medication does is eliminate any larvae that have been transmitted in the last 30 days – it does not have any lasting effect. By being late with a dose, even by a week, you allow larvae to slip through this window of effectiveness and develop into adult heartworms.

What to do if you miss a dose

When you realize you have missed a dose of heartworm medication, first figure out how late the dose is. If it is less than a week late, administer the dose immediately then recommence a regular dosing schedule. If it is more than a week late, you may want to contact your veterinarian before administering any further heartworm preventatives. Giving preventative medication to heartworm-positive animals (dogs in particular) can cause them problems.

In either case, you may want to speak to your vet and ensure that you have a heartworm test scheduled in the next 6 months.

Testing for heartworm

If you have missed a heartworm dose and suspect that your dog or cat is at risk of heartworm, you will need to have your vet perform a test. In fact, even animals on regular heartworm preventatives should be tested regularly.

The lifecycle of heartworms determines when your animal should be tested, as they can take 6 months from initial infection to develop into adult heartworms. In the case of a missed dose, your pet will need to be tested 6 months after the last dose of medication that they received, as they will have been susceptible to infection from this date.