Safety Tips for Using Heartworm Preventive Medications on Cats

Heartworm disease is a deadly disease in cats that is spread by infected mosquitoes. Unlike dogs, cats have no approved medications available to treat heartworm infection, making heartworm prevention especially important.  

Heartworm preventives for cats come in two different forms: oral medications, which are bite-sized flavored pills; and topical medications, which are put on the back of the cat’s neck.  

While all heartworm preventives are safe, effective, and made to be used easily, pet parents should carefully follow their veterinarian’s guidance on proper dosing, correct product usage, and proper medication storage. Veterinarians can also advise pet parents about what to do if a dose is missed and how to watch cats for rare—but possible—side effects. 

Safely Give Heartworm Preventives to Cats

• Stick with “cat” products. Heartworm preventives are FDA-approved products that go through careful safety testing before being approved. While many preventives for cats are also marketed in dog versions, cats should only be given medications that are made for them. Purchasing heartworm preventives from reliable sources is essential, and pet parents should always check that the source guarantees their products. 
• Deliver the right dose. Dosing of medications is decided by weight. Giving too high a dose of preventive can cause bad reactions such as seizure or hypersalivation, while giving too low a dose can put a cat at risk of being unprotected from heartworms. It’s important to keep an eye on a cat’s weight to be sure the pet is always getting the right medication dosage. Weight changes due to growth in kittens or weight gain or loss in adult cats can result in a cat needing a different dosage. 
• Give medications on time. Heartworm preventives work by getting rid of infections that took place the previous month or months (options include both monthly and every-other-month products). Because medications can only kill off early-stage heartworms, missing just a dose or two of preventive can put a cat at risk for serious infection.  
• The American Heartworm Society recommends year-round prevention for cats, including both indoor and outdoor cats. Not only does this ensure cats are protected, but staying on a 12-month schedule also helps giving the medicine become a healthy habit. 

How To Pick Your Preventive

While all FDA-approved products are highly effective in preventing heartworm infection, medications differ in two important ways: how they are given (oral or topical) and which parasites they prevent in addition to heartworms.  

Some medications only prevent internal parasites—including intestinal parasites, such as roundworms and hookworms—while others also control external parasites, such as fleas, ticks and mites. A variety of factors, from location to lifestyle to other pets in the household, can all affect a cat’s parasite prevention needs. 

Regardless of which preventive is chosen, households with multiple cats should treat all cats on the same day to avoid missed or forgotten doses. 

Oral Preventives 

For cats who are highly food motivated, a monthly oral heartworm preventive, which can be hidden in food or given as a treat, can be a good choice. Pet parents should watch their cat during and after giving the pill to make sure they swallow the entire tablet. If a dose is missed or a cat fails to eat all the medication, a veterinarian can tell pet parents when to give the next dose. 

Side effects from oral preventives are uncommon. Gi upset and vomiting, which typically resolve within 24-48 hours, are the most common side effects and can sometimes be prevented by giving the medication with a small meal. More serious reactions, such as loss of coordination, are possible but rare. Allergic responses are also rare but possible, with signs including itching, hives, face swelling, seizures, or shock. Such signs should be reported to a veterinarian immediately. 

Oral products that are currently available control hookworms and roundworms as well as heartworms. Kittens as young as six weeks (1.5 pounds) can be started on oral prevention. 

Topical Preventives 

Topical products are a good choice for cats who aren’t food motivated and for pet parents who want to control external parasites as well as heartworms and other internal parasites with one medication. These products are applied on the back of the neck or base of the skull to keep cats from licking the treated area.  

If multiple cats are being treated, they should be kept apart for at least two hours (the amount of time it takes for the product to be fully absorbed). This helps them avoid grooming each other and licking off the medication. 

Some topical products are given monthly while others are given every other month. To apply the product, cats should be placed in a calm, comfortable position—either on a flat surface or lap—or one person can hold the cat while another puts on the product. Once the cat is in position, the hair on the application area should be parted and the product applied to the bare skin. Giving treats during this process can help the application go smoothly. 

Potential side effects with topical preventives are rare, and can range from hair loss or irritation at the application site to vomiting and diarrhea, as well as more serious signs such as drooling, panting, and trembling. Allergic reactions such as those seen with oral medications (see above) are rare but can also occur. Again, any suspected side effects should immediately be reported to the veterinarian. 

After putting the product on their cat, pet parents should wash their hands thoroughly with soap and water. Treated cats should be kept away from children and other pets for two hours. 

Some topical preventives can be given as early as eight weeks of age while others should not be given until the cat is six months old. All topical products are approved to treat heartworms and intestinal parasites as well as fleas. Some products also treat ticks and/or mites, so the product choice should meet the cat’s parasite control needs. 

Other Considerations in Choosing/Giving Heartworm Preventives

If pet parents are unable to give their pet a heartworm preventive themselves, they can consider hiring a pet service to come to the home to give the product or talk to their veterinarian about having it done at the clinic.  

While heartworm preventives can be safely given along with other prescription medications and supplements, pet parents should talk to their veterinarian about any potential interactions and discuss if cats have underlying health conditions that might affect their choice of preventive.  

Safe Storage of Heartworm Preventives

As with all medications, follow these safety practices: 

• Keep products away from heat and moisture. 
• Keep products out of reach of pets and children. 
• Store products in their original packaging to avoid product mix-ups. 
• Check expiration dates to ensure products are at their full strength.