Selamectin for cats is a topical medication applied to the skin. It works to kill and prevent certain external and internal parasites, including fleas, heartworm infection, ear mites, and intestinal worms. It is found in a range of common anti-parasite treatments.
In this article, you’ll learn how selamectin works, what parasites it is effective for, potential side effects to be aware of, and some frequently asked questions.
Selamectin for Cats
About Selamectin for Cats
Selamectin is an avermectin parasiticide designed to kill and prevent specific parasites. Selamectin is found in topical products applied to the skin. Revolution is the first brand that contained selamectin as an active ingredient and is the most recognizable. Now, there are several brands that contain selamectin in the US including Revolt, Selarid, Senergy, and Paradyne. Brands found in Canada include Selevectine and Evicto. In Europe, brands include Stronghold and Chanhold.
In cats, selamectin is indicated and FDA-approved for:
- Prevention and control of flea infestations (Ctenocephalides felis)
- Prevention of heartworm disease (Dirofilaria immitis)
- Treatment and control of ear mite infestations (Otodectes cynotis)
- Treatment and control of roundworm (Toxocara cati) and hookworms (Ancylostoma tubaeforme).
It is important to note that selamectin is one of the only products approved in cats for heartworm prevention.
Off-label use of products, where the product is not specifically licensed for this use but is widely adopted anyway, is very common in veterinary medicine. Selamectin has proven to be effective off-label for the treatment and control of various mite infestations, including notoedric mange (Notoedres cati), sarcoptic mange (Sarcoptes scabiei) and Cheyletiellosis (Cheyletiella).
Selamectin has a limited ability to kill and prevent ticks and control tick infestations. It is only indicated for treatment of the American dog tick (Dermacentor variabilis). Selamectin may also be found in combination products like Revolution Plus, which contains sarolaner, an ingredient that makes it much more effective for the treatment and prevention of ticks.
Selamectin works by enhancing the release of gamma amino butyric acid (GABA), a chemical involved in nerve conduction. By enhancing GABA release, selamectin causes paralysis and death of affected parasites. Some other intestinal worms like liver flukes and tapeworms do not use GABA, making selamectin ineffective against them.
Unlike most other topical products (such as fipronil), selamectin is absorbed systemically by the body after being applied to the skin. While pesky pests like fleas and mites can be killed by coming in contact with the skin of a cat treated with selamectin, it is important to note that selamectin products do not provide true repellency. According to Revolution’s label, the product can start killing adult fleas within 12 hours with a majority killed within 24 hours. It may take a couple of days for the full effects to be seen on a heavy infestation of fleas.
Dose for Cats
The recommended dose of selamectin for cats is fairly standard, even for generic products. Selamectin is approved for cats eight weeks of age and older. All body-weight dosing is based on the original label for Revolution for cats.
- Cats/kittens ≤ 5lb: 15mg vial
- Cats 5.1lb to 15lb: 45mg vial
- Cats 15.1lb to 22lb: 60mg vial
Selamectin products should be used every 30 days for the best protection.
Revolution is considered to be waterproof within 2 hours of application. However, the manufacturer recommends waiting 24 hours after applying selamectin to bathe a cat if possible. Applying to wet skin/fur or too soon after a bath will affect selamectin’s absorption by the body and therefore the effectiveness of the product.
How to Administer Selamectin to Cats
Selamectin comes in many products, including those used in puppies and dogs. Always read instructions very carefully for any topical product prior to application, making sure the product is approved for use in cats, and for the correct weight band.
For the original Revolution product, open the blister pack and remove the small vial. The vial has a cap that must be pushed down to puncture the vial itself. The cap can then be removed and the entire contents of the vial applied to the skin.
The site of application should be the base of the neck/head, just in front of the shoulder blades. This area is the hardest for a cat to reach and greatly lowers the chance that the product can be licked off. The haircoat needs to be parted when applying so that the product is applied to the skin itself rather than the fur.
Application of a topical product is not typically stressful for a cat, though some cats may not like the sensation of the liquid application on the skin. Choose a time when your cat is calm, preoccupied, or resting. This may be on your lap, in a favorite snoozing location, or while eating a meal.
Side Effects of Selamectin for Cats
Selamectin products are typically safe when used as directed and side effects are uncommon. You may see some clumping of hair, stiff hair, or a slightly powdery residue after application—this is normal and temporary.
Topical products containing selamectin should never be ingested. Accidental ingestion from licking a product off may commonly lead to hypersalivation (drooling) and signs of vomiting. This is typically a bad taste response versus a true toxicity. The most common side effect reported during safety studies for Revolution was temporary hair loss at the treatment site. This occurred in about 1% of cats. Other side effects were seen in less than 0.5% of pets, including vomiting, diarrhea, and muscle tremors.
In 2021, post-approval experience data was released, which listed side effects reported to the FDA. It is important to note that when side effects are reported to the FDA, these may not always be directly attributable to a product. These are listed in decreasing order of frequency reported (the percentages themselves were not available):
- Application site reactions (hair loss, redness (hives), pruritus (itching), inflammation, blisters, excoriations, hair discoloration)
- Lack of appetite/anorexia
- Generalized itching
- Poor balance/incoordination/ataxia
- Generalized hair loss
- Excessive drooling
- Skin redness/erythema and inflammation
A mutation in the MDR1 gene in dogs was discovered in 2001, which makes some dogs have serious adverse reactions to medications including avermectins like selamectin. In early 2022, researchers at Washington State University also discovered this same mutation in cats. Unlike in dogs, no breed predisposition has been found in cats, but the prevalence of the mutation is thought to be about 4% of the cat population, including about 4 million cats in the US. Cats with this mutation may have more serious adverse reactions to selamectin products, including seizures, tremors, and death. The mutation also affects reactions to several other types of medications. WSU does have testing available to detect the gene mutation.
Overdose and Emergencies
If you are ever concerned that your kitty may have developed side effects while using a selamectin product, if ingestion of the product is suspected, or if the wrong size of vial is applied, immediately contact one or more of the following for advice:
- Your veterinarian
- ASPCA Animal Poison Control Center (1-888-426-4435)
- Pet Poison Helpline (1-855-764-7661)
Selamectin products can cause irritation of the skin and eyes in people. Make sure to wash your hands after applying the product to your cat.
Potential Drug Interactions With Selamectin
No drug interactions have been documented with selamectin. During clinical studies for Revolution, selamectin was used safely with vaccines, deworming products, other anti-parasitics, antibiotics, steroids, soap, shampoos, and dips (used for external parasite treatment).
Selamectin alone has limited tick control capability. However, the more recent addition of Revolution Plus, which has better tick control, has reduced the need to give cats two separate topical products if tick control is a concern.
Frequently Asked Questions
What products contain selamectin?
While Revolution was the original product containing selamectin, there are now many generic products that contain it. Besides Revolution for cats, these include:
- Revolt (US)
- Selarid (US)
- Senergy (US)
- Paradyne (US)
- Selevectine (Canada)
- Evicto (Canada)
- Stronghold (Europe)
- Chanhold (Europe)
Revolution Plus also contains selamectin in combination with sarolaner. The addition of sarolaner provides better protection against ticks.
Why is selamectin prescription only?
Although applied topically, selamectin is absorbed systemically by the body. This is why it is effective against mosquito-borne heartworms and intestinal roundworms and hookworms. Because of its systemic absorption, it falls under FDA regulation and requires a prescription. By contrast most other topical parasiticide medications are absorbed only by the skin and fall under EPA regulation, allowing them to be sold over the counter.
What if I miss a dose of selamectin?
If you miss a dose of selamectin, there may be a gap in protection, but it is okay to give the next dose as soon as you remember. However, it should not be applied more often than every 30 days, so make sure to move the next date of application forward 30 days. If you are uncertain if a dose was applied properly, or if you are concerned that you still see fleas on your cat after applying a selamectin product, it’s best to give your veterinarian a call for advice instead of applying an additional dose.
How long does it take selamectin to work in cats?
Selamectin products can take a little longer to work completely compared to some other flea/tick products. According to Revolution’s label, fleas will start to die within 12 hours with a majority killed within 24 hours. When used as a preventative prior to flea exposure, Revolution will start killing fleas within 6 hours with a majority killed at 12 hours.
In the case of very heavy flea infestations, fleas may continue to hatch in the environment and be seen jumping on a cat. Very few topical products in cats provide any repellency and fleas must come in contact with the skin to be affected. In these cases, it may take up to a week for complete flea control depending on how bad the environment is affected to see complete effects.
How long can cats take selamectin?
If a cat has not demonstrated any adverse reaction signs to selamectin, there is no reason a product cannot be continued for the life of a cat. Selamectin can be used year-round. After over 20 years of being available on the market, there have not been official reports of selamectin becoming less effective for a cat over time or the risk of side effects increasing over time (if all else is unchanged with a cat’s general health condition).
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