Is it Safe to Use Expired Heartworm Meds for My Dog?

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Heartworm disease in dogs is a serious health issue caused by a parasitic worm. It is spread through mosquito bites. Pet parents are advised to give their dogs heartworm medication year-round to protect their dogs not only against heartworm but against a variety of intestinal parasites (depending on the brand, this medication may also protect against roundworms, hookworms, whipworms, and tapeworms). Since some parasites are contagious to humans, this medication can protect both human and canine family members. But what happens when the medication is past its sell-by date?


Dogs get heartworms from mosquito bites.

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Does dog heartworm medicine expire?

Yes, heartworm medicine expires.‌ There's a reason there's a date on the package, and that expiration date tells you for how long the medicine is safe and effective. The active ingredient insecticide used to kill heartworms, usually milbemycin oxime or ivermectin, might not be at full strength after the expiration date, or it might not work at all.


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Expiration dates are established by the U.S. Food and Drug Administration after careful testing to ensure that the medicine will be effective at the time of use and has undergone no significant deterioration.

Can you use expired heartworm medicine?

No, you should not use expired heartworm medication.‌ As with all drugs or medicines, heartworm preventives should be used before the expiration date on the package because it is impossible to predict whether it will be effective or safe once it has expired.


What do experts say about using expired heartworm medication?

The American Heartworm Society recommends that any expired heartworm medication for dogs and cats be thrown out.‌ If your medicine is past its shelf life, it's no longer guaranteed to be effective. However, it's important that expired pet health products be properly disposed of. Flushing them down the toilet can contaminate the local water supply.


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How should pet owners dispose of prescription medication?

A veterinarian or local pharmacist can dispose of expired heartworm medicine for you.‌ If you prefer to dispose of it yourself, here are some simple steps to ensure the drugs do not harm anyone else.


  • Take the drugs out of their original container. If they are in a vial with your name, address, or any personally identifying information, cross out the information to protect your privacy.
  • Mix the drugs with something unappealing (coffee grinds, rotted food, dirty diapers) so that stray animals going through your garbage don't take it. This also makes it less likely that people going through garbage looking for drugs might be enticed by it.
  • Put the drug mixture in a closed container that can be sealed to keep the contents from leaking.
  • Throw away the container and cover your garbage can tightly.



How long is heartworm medication good for?

The expiration date on all dog medications is the date after which the product can no longer be legally sold.‌ If it's a few days past the expiration date, you can safely give it to your dog. However, if it is a month or more past the expiration date, you should just toss it.


What if my dog's heartworm pill expires before the month is over?

Ask your provider for a package with a longer expiration date.‌ If you begin using a package of one-dose-a-month heartworm medication and realize the expiration date will occur before you'll have used it all, contact the veterinary hospital where you purchased it and ask for a box with a longer expiration date.


What will happen if you give expired heartworm medication to your dog?

Simply put, the heartworm medication may not work.‌ This means your dog could be at risk for heartworm infection, which is a serious and painful illness that can result in lung disease, heart failure, organ damage, and even death. Why risk it to save a few dollars?

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How to avoid expired heartworm prevention meds

Always check the expiry date of the heartworm medication before purchasing to be sure the medicine will not expire before all of the tablets can be used.‌ If you are ordering through an online service, check the dates when it arrives before you open the box to make sure the pet medication will be good for the full course of use. If the expiration date would come up before you'd complete the full course of medication, contact the company to exchange the medication for a newer box.


Types of heartworm medicine

There are a variety of heartworm medicines designed with pet safety and convenience in mind, from chewable tablets and topical formulas to FDA-approved injectable treatments.

Some popular heartworm medication brands include:

  • Heartguard Plus
  • Interceptor Plus
  • Revolution
  • Sentinal Spectrum
  • Simparica Trio
  • Trifexis
  • Advantage Multi
  • Tri-Heart Plus

The life expectancy may vary among brands, but each one should have a listed expiration date so you know you're never getting expired medications.

Heartworm medication warning

Dogs over 7 months old that are starting heartworm medication for the first time should be tested for adult heartworms prior to being given any heartworm drugs. Giving a heartworm preventive to a dog infected with adult heartworms can be dangerous or even fatal. If there are already microfilariae (immature worms) in the dog's bloodstream, the preventive may cause the microfilariae to die suddenly, creating a shock-like reaction that could be deadly.

Some heartworm medications only kill immature heartworms in the bloodstream but not adult heartworms. Ivermectin-based heartworm preventatives will kill adult heartworms, but this is a lengthy process that can take as long as a year or more. During this time, the dog's lungs are still being adversely affected by the parasite, so if your dog has heartworm, you'll want to consult with your veterinarian to ensure the best course of treatment for your dog.

The bottom line

Heartworm is a serious, painful, and potentially fatal disease that can be prevented by giving your dog heartworm preventatives regularly. However, if the medicine is expired, it may not be safe or effective. While giving medicine a few days past its expiration date is OK, the best way to keep your dog safe is to read the expiration date before buying it and toss anything that's expired.