By Jennifer Kvamme, DVM
Keeping our cats free of heartworms is much cheaper, easier, and safer than treating them for the full-blown disease. However, it is important that you use heartworm preventives properly -- both for your safety and your cat's safety.
When deciding which heartworm medication to give your cat, you should always ask your veterinarian for advice first. It’s very important that you purchase the correct dosage for your cat, and that you use only approved medications for your cat’s particular age, weight, and health status. Also, your veterinarian will only give you a prescription for a preventive if the cat is shown to have no heartworms (tested negative).
There are several kinds of heartworm preventive medications commonly used today. Many of these medications have multiple benefits; some control intestinal parasites and external parasites, in addition to preventing heartworms.
Common active ingredients used in heartworm preventive medications today include ivermectin and milbemycin. Ivermectin has been used for decades to prevent heartworm disease in cats. There are rarely side effects, if given at the proper dosage. Some reactions that have been reported in animals are vomiting, diarrhea, and loss of coordination.
In the case of allergic responses, there have been reports of itching, hives, swelling of the face, and even seizures or shock. Observe your cat for anything out of the ordinary after each administration of this medication, since sensitivity can come on suddenly, even after prolonged use of a medication.
Newer topical or spot-on medications are available to prevent not only heartworms, but also fleas, ticks, mites, and more. Depending on the brand you choose, your cat can be protected from many parasites, both internal and external, all in one monthly application. Selamectin and moxidectin work by absorbing into the animal’s skin and collecting in the oil glands under the skin. From there, the drug dispenses slowly over time, protecting the cat.
When applying these types of medications, you want to be careful not to get it on your skin or in your eyes. The fur in the area between the shoulder blades should be separated, to find the skin below. Apply the liquid directly to the skin instead of to the fur. Wash your hands after handling these medications (or wear disposable gloves so there is no skin contact at all). Label instructions should always be followed carefully. Keep your cat indoors and watch him/her for about 30 minutes following application. Children and other animals should be kept apart while the medication is absorbing. This is especially important if you have more than one cat, since a cat may accidentally ingest the medication while grooming the other (treated) cat.
Adverse reactions to these medications are rare, but do occur. Possible side effects can include vomiting, diarrhea, drooling, panting, and trembling. Some cats can have an allergic reaction to these types of medications, similar to the reaction seen with ivermectin. Hair loss at the application site has also been reported.
Here are just a few more basic tips to consider when giving your cat heartworm preventives:
Any type of arachnid excluding ticks
Swellings under the skin that can be caused by food allergies or anything else