When Should I Start My Dog On Heartworm Prevention?

Does my dog really need to be on heartworm prevention already? He’s just a puppy. Why do we need to start so soon? When should we really start? We get this question all the time – “When should I start my dog on heartworm prevention?”

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When Should I Start My Dog On Heartworm Prevention?

All dogs should start on regular heartworm prevention medicine when they are puppies. Most heartworm prevention medicines are safe for puppies as young as 6-8 weeks old. We recommend that puppies are started on heartworm prevention at their first puppy visit (usually around 8 weeks old).

It is not necessary to test a young puppy for heartworms. The tests will not detect a heartworm infection in a puppy that young. If a young puppy has been exposed to heartworms before starting the prevention medicine, the prevention should clear any infection.

If your dog is older and has never been on heartworm prevention, or if you recently adopted an older dog and are not sure of his heartworm status, he should be tested for heartworms before starting a prevention medicine. Using heartworm prevention in a dog who has a heartworm infection can be dangerous. Testing your dog for heartworms before beginning heartworm prevention medicines is important for the healthy and safety of your dog.

We strongly recommend that dogs stay on heartworm prevention medicines all year long. Heartworms are transmitted by mosquitoes, and it can be difficult to judge when mosquito season will begin. If you wait to start heartworm prevention until after you have seen a mosquito, it is highly likely that your dog has already been bitten by one. Your dog has the potential to be exposed to heartworms with every mosquito bite.

When Should I Give Heartworm Prevention?

It is important that heartworm prevention be given on the correct date, 30 days from the last dose. Even though we call them “prevention” medicines, they don’t actually prevent your dog from being bitten by a mosquito and getting exposed to heartworms. The drug in these prevention medicines kills the heartworm microfilaria, or baby heartworms. Once the baby heartworms grow into teenage heartworms, these medicines are not as effective in killing them. This growth from baby to teenager happens in 45-60 days after the infection.

If you give your dog his heartworm “prevention” on April 1, and he gets bitten by a mosquito on April 2, he can get infected with baby heartworms. If you give the next dose of prevention on May 1, that medicine will kill the baby heartworms. But if you forget to give his dose in May, and don’t give the next one until June now your dog will have teenager heartworms that are not as susceptible to the prevention medicine. Your dog could easily develop a full adult heartworm infection, just from missing one dose of his prevention.

All heartworm prevention medicines come with stickers that you can put on your calendar. You can also set reminders in your electronic calendar so you remember to give the heartworm prevention on the right day. A good rule of thumb is to make the first day of the month “heartworm day.”

If you are concerned that you may forget to give your dog the monthly heartworm prevention medicine, there is another option called Proheart 6. Proheart 6 is an injection that can be given by your veterinarian. This medicine is a slow-release heartworm prevention (a similar drug that is in the monthly heartworm prevention medicines) and will protect your dog from a heartworm infection for six months. Even better, we will send you postcard and email reminders when it is time for your dog to get his next dose! Proheart 6 can only be used in dogs older than 6 months. Puppies should start on a monthly heartworm prevention by the time they are 8 weeks old, and can start using Proheart 6 when they are six months old.

Is your dog on heartworm prevention medicines? If not, it’s time to start! Call us or come in to get any of your heartworm questions answered. We can test your dog for heartworms (if he has not been on year-round prevention, or if it has been one year since his last test), discuss your options for heartworm prevention, and decide on the prevention medicine that will be the best choice for your dog and your family.

Check out our Heartworm Disease Resource Page for even more information about heartworms.

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