Kim Carney /
updated 6/28/2005 8:44:57 PM ET 2005-06-29T00:44:57

Months of heavy rain in California, last year’s hurricanes in Florida and along the East Coast, and a mild winter and wetter-than-normal conditions in the West and Midwest all add up to one thing: the likelihood of a record number of fleas this year. Flea season has already started in most of the country, and pet owners in Texas, Florida, Pennsylvania and Northern California are among those reporting problems with the biting beasties.

So what’s the best way to tackle fleas? Happily, constant bathing, dipping, spraying and powdering are things of the past.

The latest generation of topical insecticides, combined with the use of insect growth regulators (IGRs), has made flea control easier and more effective than ever before. But are the topical flea-control products sold in pet supply stores just as effective as or even the same as those available from your veterinarian? They certainly cost less, which can be a draw if you’re a pet owner on a tight budget.

While both types of products are applied to the skin between the shoulder blades, they contain different chemical formulations. "The chemicals used in the over-the-counter spot-on once-a-month formulations are in general less effective ... and don’t have the safety profile that the major commercial spot-on preparations have that are [available from veterinarians]," says Peter J. Ihrke, a veterinary dermatology specialist at the University of California, Davis.

"Over-the-counter spot-on preparations have a chemical called permethrin in them," he says. "Permethrins can be reasonably effective and they’re certainly better than a lot of the products available 10 or 15 years ago … but many of the permethrins cannot be used on cats. With many of the permethrin products, we’re reluctant to recommend using them on a dog in a household if there’s also a cat living in the same house."

Hartz product phaseout
Ihrke’s point is borne out by the announcement on June 3 by the Environmental Protection Agency (which regulates insecticides) that because of adverse side effects and some reported deaths, the Hartz Mountain Corporation will stop producing Hartz Advanced Care 4 in 1 Flea and Tick Drops Plus for Cats and Kittens, Hartz Advanced Care 3 in 1 Flea and Tick Drops for Cats and Kittens, and Hartz Advanced Care Once-A-Month Flea and Tick Drops for Cats and Kittens.

The active ingredient in these products is phenothrin, a synthetic pyrethroid that kills adult fleas and ticks. Pyrethroids, which include pyrethrin and permethrin, are insecticides derived from the extract of a chrysanthemum species. Other over-the-counter products contain different forms of pyrethroids and some contain insect growth regulators, which prevent flea eggs or larvae from developing to maturity. Some may contain phenothrin, but at lower concentrations.

Their overall drawback is reduced effectiveness. After being in use for more than 20 years, the effectiveness of pyrethrins has decreased substantially because fleas have developed resistance to these types of chemicals.

The active ingredients in veterinary topicals — fipronil, selamectin or imidacloprid — kill adult fleas when they touch the animal’s skin. "These products are much more effective, safer, easier, and in the long run, more economical than anything we had before," says Link V. Welborn, a veterinarian at North Bay Animal and Bird Hospital in Tampa, Fla.

As yet, resistance doesn’t appear to be a problem with veterinary topicals. "You always worry [about resistance developing]," says Dennis A. Feinberg, a veterinarian at Charles Towne Veterinary Clinic in Charleston, S.C., and immediate past president of the American Animal Hospital Association. "With the time they’ve been on the market now, my experience so far is I haven’t seen a change of losing the efficacy of the product, but as time goes on there’s going to be mutations among fleas and they’re going to have to put some kind of twist on it chemically."

Like over-the-counter spot-ons, spot-ons that are strictly insecticides such as fipronil (Frontline) or imidacloprid (Advantage) are regulated by the EPA and are not prescription products, but their manufacturers have chosen to market them primarily through veterinarians to ensure that their use is properly explained.

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"Individualizing flea control by reviewing the lifestyle and environment of the pet with the client is important," says Welborn. For instance, the average dog or cat often does well with having only a spot-on treatment applied every month or so, but severely flea-allergic animals may need a spot-on, plus an insect growth regulator such as lufenuron (Program).

Be aware of side effects
Can veterinary spot-ons have side effects? Any medical product can, no matter what its safety record. Dogs and cats are individuals, and what works well on one can adversely affect another, depending on factors such as age and health.

Ihrke says that in general it’s a good idea to have an assessment of the overall health of an animal before using any medical product. "There certainly can be adverse side effects ... and there are certain oral or injectable prescription medications on the market that have the potential for interacting with some of the topical products, so it’s more of a safety issue," he says.

If you’re concerned that such products could be harmful, Welborn suggests looking at the risk-to-benefit ratio. "Safety should be considered in terms of relative risk. The risk associated with not controlling external parasites and not preventing heartworms [in the case of combination flea control/heartworm products such as Sentinel] is much greater than the risk of any potential side effect with these products," he says.

That’s all well and good unless you’re the owner of the pet having a reaction to a product. To prevent problems, take the following precautions:

  • Read the label carefully before applying any product to your dog or cat to ensure that it’s appropriate for your pet’s species, age and weight.
  • If you don’t understand exactly how a product is to be used, ask your veterinarian.
  • Never apply products meant for dogs to cats, or vice versa.
  • Make sure that a particular product is safe for use on puppies, kittens, pregnant animals or old animals.
  • Give oral flea treatments with food to prevent stomach upset.
  • If your pet shows signs of reacting to a spot-on product, such as acting "drunk" or frantic, redness at the application site or severe itching, bathe him and then take him to the veterinarian to make sure he’s OK.
  • Never assume that more is better. Too much of any product, especially in cats, can have serious or even fatal consequences.

Kim Campbell Thornton is an award-winning author who has written many articles and more than a dozen books about dogs and cats. She belongs to the Dog Writers Association of America and is past president of the Cat Writers Association. She shares her home in California with three Cavalier King Charles Spaniels and one African ringneck parakeet.

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