Comfortis for Use in Cats: Is it Safe and Effective?

Cats are fastidious and many dislike having smelly topical products applied to the fur. But until now, there have not been many alternative products that cats can take orally to treat fleas, except the over-the-counter products, Capstar and Program. These treatments have limitations: Capstar treats adult fleas, but the effect does not last beyond 24 hours.  While Program works for 30 days to prevent the development of flea eggs, it does not kill adult fleas. Hence, for maximum effectiveness these two products should be used together. Cat owners will be happy to know they now have another option in Comfortis.

Comfortis (spinosad) is a chewable once a month oral medication used to treat and prevent flea infestations. Since 2007, Comfortis was only used for dogs but now as of August 2012 the FDA approved 4 different strengths for cats 14 weeks of age and older, who are greater than 2 pounds.

Comfortis for cats was found to have minimal side effects with no major or life threatening side effects reported. The main side effects found when using Comfortis in cats were vomiting, lethargy, anorexia, weight loss, and diarrhea. Vomiting was found to be the most significant side effect, occurring in 39 out of 139 (28.1%) of cats the day of or the day after Comfortis was given compared to 2 out of 72 (2.8%) using the topical formulation. The manufacturer suggests giving another dose if your cat vomits within 1 hour of administration.

The effectiveness of Comfortis is high. In clinical trials it began to kill fleas in the first 30 minutes and had a 98% effectiveness rate after 4 hours. It had a 100% effectiveness rate the day after the dose and a 90% effectiveness rate on day 30. The manufacturer also conducted a field study with cats in a flea infested environment and found a 99% effectiveness rate after 3 months.

Comfortis has demonstrated that it is safe and effective in cats, with a high efficacy rate and no major side effects. It has many advantages: it works fast, is safe and effective, it is easier to administer than topical products, won’t wash off, and no isolation from children is necessary after administration. It does have a few limitations however; vomiting can be problematic occurring in 1 out of 4 cats, it is more expensive than older flea treatments, and it is new to the market and long term effects of Comfortis have not been studied.

As every cat is different it is impossible to know what side effects, if any, your cat will experience and how effective the medication will be. Therefore, it is important to talk to your veterinarian to determine if the benefits outweigh the risks before starting your cat on Comfortis.