The Ins and Outs of Heartworm Medications for Cats

3 min read

Reviewed and updated for accuracy on April 29, 2019 by Dr. Hanie Elfenbein, DVM, PhD

As a cat owner, keeping your cat free of heartworms is an important job. It’s your responsibility to give her preventative heartworm medication for cats every month.

While you may have been doing this for some time now, have you ever wondered just how these pet prescription heartworm medicine prevent heartworm disease in your cat?

How Does Heartworm Medication for Cats Work?

You may be surprised to learn that heartworm preventatives do not stop the actual infection from occurring in your cat. If an infected mosquito happens to bite your cat, they may still be infected with the larvae.

Heartworm medications for cats work to kill off the larval heartworms that made it into the cat’s body during the past month. The worms are killed at certain stages of development, before they can become adult heartworms. However, preventatives will not kill adult heartworms.

Why Cat Heartworm Medication Should Be Given Monthly

There are many choices for heartworm preventive medication, from topical products to chewable oral medications; most come in both dog and cat versions.

Although hearworm medications for cats require monthly administration, they do not actually stay in your cat’s bloodstream for 30 days. The active ingredients work to kill any larvae that have been in the system for the past 30 days, clearing the body each month.

The heartworm medication is only needed once a month because it takes longer than a month for the larvae to develop to a stage where they reach the body tissues.

Why Heartworm Medication for Cats Requires a Prescription

So, why do you need a prescription from your veterinarian to be able to purchase heartworm medication at a pet pharmacy? Heartworm medications for cats are regulated by the FDA and, therefore, require a veterinarian’s prescription.

Your veterinarian will also want to make sure that your cat doesn’t have an active infection of heartworms before giving a preventative medication.

Animals with active infections can have a severe, possibly life-threatening reaction to the dying, circulating microfilariae (adult heartworm offspring) if given these medications. The reaction can send the body into a shock-like state that can be fatal.

Therefore, the rule is in place so that your veterinarian has the opportunity to make sure that your cat is a good candidate for heartworm prevention before you administer it.

Why You Should Give Heartworm Preventatives Year-Round

Veterinarians also now recommend that cats be given heartworm preventative all year. It has always been the case in warmer climates where mosquitoes are present all year long, but has now become the norm throughout the rest of the country.

Where mosquitoes are less active in the winter months, cat owners have gotten into the habit of only treating their cats for half the year. But because of unpredictable seasonal temperature changes, the American Heartworm Society is now recommending year-round prevention for animals in every state. This is a good practice to help you remember to always protect your cat from heartworms, no matter what the season.

Also, your cat does not need to go outside to be at risk for heartworm disease. Mosquitos easily sneak into homes. Make sure your cat is protected.

Another reason for year-round prevention is that some heartworm preventatives contain medications that also remove other parasites, such as fleas, mites, ticks, roundworms, hookworms and whipworms.

Depending on which heartworm medication you choose for your cat, he/she may also be protected year-round from these parasites.

Ask your veterinarian for help in choosing the best possible heartworm preventive medication for your cat.

By: Dr. Jennifer Kvamme, DVM

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