Flea Control

Teri Dickinson, DVM

Recently, three completely new prescription-only products for flea control have been released in the US. This article is intended to give readers a better understanding of the actions of these products. As always, your veterinarian is your best source of information about which of these products is most appropriate for your situation. Several of these products have been available in England, Australia and/or Europe for several years, so international readers may recognize these as products they are already using.

Traditional flea control relied on the use of insecticides, usually of the organophosphate or pyrethrin class. As newer products evolved in each class, safety and efficacy (effectiveness) improved; however, one basic principal did not change. All of these insecticides were designed to kill fleas by interfering with certain biological mechanisms in the flea. Unfortunately, these same mechanisms were found in the hosts (dogs and cats) and killing fleas was a matter of using enough insecticide to kill the flea, but not enough to kill or injure the host. Needless to say, this goal was not always met.

The first real breakthrough in flea control came through the use of insect growth regulators (IGR's) which were hormones that interfered with the reproductive cycle of the flea, but had no deleterious effects on the host. By preventing fleas from reproducing, a population of animals could be made flea-free, or at least have greatly reduced flea numbers.

While IGR's contributed greatly to flea control, several disadvantages remained. Most break down rather quickly in the presence of sunlight, so their effectiveness as outdoor premise sprays or on animals was limited. In addition, because they do not kill adult fleas, several weeks were necessary to see a reduction in flea population as existing adults died off and no young adults took their places.

The new products recently approved in this country are lufenuron (Program marketed by Ciba-Geigy), imidacloprid (Advantage-marketed by Bayer) and fipronil (Frontline-marketed by Rhone Merieux). Program is classified as an insect development inhibitor (IDI) and Advantage and Frontline are insecticides (or more correctly, ectoparasiticides) that kill adult fleas. All three employ actions not previously available for flea control in this country.

As previously stated, all of these products are available by prescription only, from a licensed veterinarian. They are not inexpensive compared to older formulations, but may present advantages that outweigh cost considerations. In addition, they may be cost effective in the long run, as they do not require frequent usage.

Program was the first of these new generation flea control products. Its action is to interfere with the production of normal eggs within the adult female flea. Program does not kill adult fleas. It should be started prior to the advent of flea season, or if used on flea infested animals, should initially be supplemented with an insecticide. Three to four weeks are required in most cases to see an effect from Program alone, as again, it interferes with the life cycle, but does not affect adults.

Program is given orally as a tablet in dogs, or a liquid suspension in cats.Program is now also available in an injectable form for cats which is administered every six months. It is important to treat all animals in the household, as untreated animals will serve as a source of reinfestation for treated animals. In order for Program to be correctly absorbed from the intestinal tract, it must be dissolved in fat. Therefore, a full meal (preferably a high fat meal) must be fed prior to giving Program. It is administered every thirty days, and once absorbed into the body, is stored in the fat and slowly released into the animal's bloodstream. When the adult flea takes a blood meal, the Program is taken in by the flea, and interferes with egg production.

Program is approved for both dogs and cats six weeks of age and over. Because it is not an insecticide, it does not add to the toxicity of other insecticides. Therefore, as stated above, insecticides may be used initially along with Program in order to control existing adult flea populations, and kill new juveniles as they hatch from eggs laid prior to the administration of Program. A potential disadvantage to Program is that the flea must bite the host in order to ingest the drug. For dogs with flea bite allergies, even a few bites can cause severe itching. An advantage is that Program is considered extremely nontoxic to mammals because it interferes with the reproductive processes of the flea, which are not found in mammals. Program has been in use in other countries for 3-4 years, and appears to have a good safety record.

The next entry into the flea control foray was Advantage. Advantage kills adult fleas on the host, by interfering with normal nerve transmissions, affecting a pathway that is more important in insects than mammals. As a result, Advantage should be toxic to fleas, with minimal toxicity to mammals.

Advantage is applied as a topical solution to either dogs or cats. A small tube of liquid is applied to the skin between the shoulder blades. Natural movement of the animal causes the substance to be distributed all over the surface of the skin. Advantage has minimal absorption through the skin, further lessening the chances of toxicity in the animal. Advantage kills fleas on contact, and is reported to kill 98-100% of adult fleas within 24 hours of application. Advantage is reported to be safe for use on puppies and kittens, although no minimum age is given. Advantage is reported to control fleas for at least thirty days in dogs, although this may be reduced if the dog swims or is bathed frequently.

The most recently approved product in the US is Frontline. Frontline kills adult fleas by inhibiting GABA, a substance used to transmit nerve impulses in insects. GABA is a less important substance in mammals, and therefore, even though Frontline effectively kill fleas, toxicity to mammals is very low. Frontline is applied as a pump spray, or a topical solution. It works its way down into the hair follicles and is present on the body for several months. When applying Frontline, it is important to wet the skin and rub the hair the wrong way, in order to properly penetrate to the skin.

The spray is flammable, (as are many flea sprays) and should not be applied in the presence of an open flame, nor should the animal be exposed to flames until it is completely dry. Plastic gloves should be worn while applying the spray. Once dry however, there is little absorption through the skin so the animal has minimal exposure, and pets are safe to handle once dry.

Duration of efficacy against fleas is reported as three months in dogs, and two months in cats. Because the product is down in the hair follicles, normal bathing or swimming has no significant effect on the duration of efficacy. In addition, Frontline provides protection against ticks for up to one month (the only one of these products labeled for ticks) and animals may be safely retreated as often as once a month.

Frontline is labeled for use in dogs two days of age or older, and cats seven weeks or older. In addition, Frontline is reported to be safe in pregnant and lactating bitches. Treatment of carpets, bedding etc. with a suitable insecticide is recommended to reduce the numbers of fleas in the environment and extend the duration of Frontline's efficacy. Frontline was developed in England and has been used extensively there.

A potential advantage to both Advantage and Frontline is that they kill fleas relatively quickly and should greatly reduce the number of flea bites suffered by the pet, an important consideration in cases of flea bite allergies.

As an aside, drug companies spend many millions of dollars before they are able to bring a new drug to market in this country. These new drugs are patented, and until the patents expire, no "generic" forms of these drugs will be available. Both Program and Advantage are being heavily advertised to pet owners as of this writing, and I assume Frontline will be as well. Be a smart consumer, and learn to read between the lines.

As in any field, ad writers seek to tout the advantages of their product, while exploiting the weaknesses of the competition. As an example, ads which state "Other products don't kill adult fleas" are designed to make you think a product that doesn't kill adults is completely worthless. However, if you understand the intended purposes of each product, you can make intelligent decisions about which (if any) of these products makes the most sense for your household.

As a final note, please notice that the purpose of this article was attempt to educate readers about three specific products. Many other methods of flea control exist, ranging from herbal remedies to nematodes which kill developing flea larvae. This was not intended to be an all encompassing article, but again to provide information about these new products. Readers are encouraged to learn as much as possible about all methods of flea control, and make informed decisions in consultation with their veterinarians.

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