The top two topical flea treatments for both dogs and cats are Advantage II and Frontline Plus. Both products receive mostly positive reviews from veterinarians and pet owners, but we found somewhat stronger recommendations for Advantage II. Cat owners, in particular, tend to give Advantage II for Cats (Est. $55 for a 6-month supply) high marks for its effectiveness, safety and ease of use. While it does not work for every cat, it's more consistently effective than any other topical treatment. Most owners also find it easy to apply and are not bothered by the odor. Advantage II is a reformulated version of an older product called Advantage, first released in 1996, which killed only adult fleas. The new version includes an insect growth regulator (IGR) to kill flea eggs and larvae as well. Both original Advantage and Advantage II get positive reviews from veterinarians, including those who specialize in cat care. Vets at the All Feline Hospital in Lincoln, Neb., describe Advantage II as "very safe and effective on cats." However, reviews from cat owners indicate that in very rare cases, cats may have dangerous reactions to this treatment, so it's probably wise to consult a vet before use.
Advantage II for Dogs (Est. $60 for a 6-month supply) is sold in several different formulations, for small, medium, large and extra-large dogs; as you might expect, formulations for larger dogs cost a little more than those for smaller ones. Dog owners are not quite as enthusiastic about Advantage II as cat owners. Although most owners find it effective, dog owners were more likely than cat owners to complain that Advantage II either didn't work or stopped working before the one-month treatment period was up. Also, while a couple of vets recommend original Advantage for dogs, we did not find any reviews that specifically discussed the pros and cons of the reformulated version.
Frontline Plus, like Advantage II, is a reformulated version of an older product. The original Frontline killed adult fleas, as well as lice and ticks. The new version, Frontline Plus, also contains an IGR to kill fleas at every stage of their life cycle. It continues to protect against ticks and chewing lice as well, something that Advantage II can't do. Frontline Plus for Cats costs about $60 for a six-month supply. Frontline Plus for Dogs, like Advantage II for Dogs, comes in four formulations for dogs of different sizes; prices average around $65 for a six-month supply.
Like Advantage II, Frontline Plus gets high marks for safety from both vets and pet owners, but it doesn't appear to be as consistently effective. The vets at Mid Hudson Animal Hospital in Hyde Park, N.Y., say that while they "would love to recommend" a cat-friendly product that kills both fleas and ticks, they "have had too many clients complain that their pets still had lots of fleas when they were using Frontline." While these remarks appear to refer to original Frontline rather than Frontline Plus, we found many reviews for Frontline Plus from pet owners that echo this complaint. Many owners note that Frontline Plus (or original Frontline) used to work for their pets and no longer does.
For dog owners who want to control both fleas and ticks, another option is K9 Advantix II (Est. $65 for a 6-month supply) , depending on the weight of the dog. Made by the same company that makes Advantage II, K9 Advantix II contains the same ingredients, plus an additional ingredient called permethrin that kills ticks and mosquitoes. Permethrin is highly toxic to cats, so K9 Advantix II is for use on dogs only. In fact, according to the "GreenPaws Flea and Tick Products Directory" sponsored by the Natural Resources Defense Council, veterinarians advise against using products with permethrin if there are any cats in the home. While permethrin is not generally considered harmful to dogs, reviews from dog owners suggest that K9 Advantix II is more likely to cause side effects than either Advantage II or Frontline Plus. Skin irritation is the most common problem, but a few owners describe more serious reactions. Still, K9 Advantix II appears to be the most effective product available for treating both fleas and ticks in dogs.