Update on treatment of flea allergic dermatitis (Proceedings)

Flea infestation and flea allergic dermatitis in both dogs and cats remains one of the most common reasons owners bring their pets to the veterinarian. In the past 20 years, the advent of new products has revolutionized our ability to control fleas and, specifically, keep flea allergic patients comfortable. Thankfully, there has been a strong trend away from toxic products and towards newer, safer products that intelligently target specific parts of the flea life cycle. The goal of this lecture is to discuss the different flea control products available that are going to be useful to the veterinarian in daily practice.

Traditional Flea Control Products

Insect growth regulators (IGR's) and insect development inhibitors (IDI's). These products effect more juvenile life stages of the flea, and are very safe and effective for both environmental flea control and on-animal use. The two currently marked IGR's in the US and Europe are methoprene and pyriproxyfen. Lufenuron (Program® and Sentinel®, Novartis) is the readily available IDI. These products are administered orally, injectably (lufenuron) or topically (pyriproxyfen, methoprene), and provide ovicidal and larvicidal effects. Unlike pyriproxyfen and lufenuron, methoprene is quickly inactivated by ultraviolet light, which is important to consider when dealing with an outdoor pet. Pyriproxyfen tends to be very long lasting and stable.

The IGR's are analogues of the insect juvenile hormone that regulates larval DNA transcription, which aids in larval formation. Other hormones subsequently trigger the decrease in juvenile hormone levels, which allows DNA that codes for adult characteristics to take effect. Pupation cannot occur if juvenile hormone levels do not drop, leading to a break in the flea life cycle. The IGR's thus cause large larvae that can't progress to their next developmental stage, or abnormal pupae, which cannot hatch. They also are ovicidal.

The IDI lufenuron inhibits chitin development if present in blood ingested by the flea (i.e. it sterilizes the female flea). It interferes with embryogenesis, hatching and molting and results in fleas being unable to exit their egg.

Many environmental foggers and sprays contain these products, and exterminators often use them.

Frontline® Spray, Frontline Plus® and Frontline Top Spot® (fipronil) - Merial

Fipronil is a phenylpyrazole, which blocks the action of GABA, an essential flea neurotransmitter. The insect growth regulator methoprene is present in Frontline Plus. These products are available as a spray (Frontline spray®, 0.29% w/w alcohol) or a convenient spot-formulation (Frontline® and Frontline plus®)(9.7%). Administering the spray at 1-2 pumps/ pound of body weight over the entire body is recommended, although the author has clients focus on the back half of the body. In general, the product has about 95% efficacy for close to a month. Patients can be bathed between applications as the product is lipid soluble and resides in the hair follicles, however it is recommended to not bathe 2 days prior or after application so that the skin's oils can aid in the product's movement over the skin. The product is also effective against ticks and cheyletiella. Fipronil is very safe with infrequent adverse reactions reported.

Advantage® (imidacloprid), K9 Advantix® (with permethrin), Advantage Multi® (with moxidectin)- Bayer Imidacloprid is the common ingredient in these products, and it acts by preventing binding of acetylcholine in the postsynaptic nerve region. These products are available as topical spot on treatments for dogs and cats. They act for approximately the same length of time as fipronil containing products, but are water-soluble and therefore more easily removed by bathing or swimming. Imidacloprid has no efficacy against ticks or apparent flea repellent effect, and the combination product Advantix® (imidacloprid with permethrin) is recommended if these qualities are desired. Advantage Multi® also contains moxidectin, making it a heartworm preventive and effective for other ectoparasites, including cheyletiella. Imidacloprid is extremely safe and well tolerated, and an especially good choice in cats.

Revolution® (selamectin) - Pfizer

Selamectin is a semi-synthetic avermectin, available as a spot on application for both dogs and cats. It is also effective against ticks, sarcoptic mange, notoedric mange, cheyletiella, otodectes, several internal parasites, and is used as a heartworm preventative.

Revolution is an efficacious and extremely safe flea control medication, even in ivermectin sensitive breeds, such as collies. It is fairly water resistant but, like the fipronil containing products, it is best to wait 2 days before and after bathing for application. This product is commonly used every 2 weeks for three or more doses to rule out sarcoptic mange.

Capstar® (nitenpyram) - Novartis Nitenpyram is a neonicotinoid flea adulticide, with a similar chemical makeup to imidacloprid, but differs as it is orally administered at a minimum target dose of 1mg/kg. It has an extremely rapid onset of action, is very short acting, and is extremely safe in both dogs and cats. It removes over 95% of adult fleas from dogs and cats within 4 – 6 hours of administration, and continues to have residual activity for an additional 48 -72 hours. This product is an excellent choice for situations where a pet may be exposed to a high burden of fleas for a short period of time, such as at the kennel, dog or cat show, dog park, or trip to the groomer. It is also an excellent choice for animals that are bathed or swim extremely frequently. Lastly, it is non-flavored and can be utilized in food trials as an oral flea control product for those owners who refuse to utilize topicals.

Newer Flea Control Products

      Comfortis® for Dogs (spinosad) - Eli Lilly

Comfortis is one of the recently released flea products that has greatly impressed veterinary dermatologists. It is only approved for use in the canine, and it is NOT advised to use it off label in cats. Spinosad has a novel mode of action at nicotinic acetylcholine D α-receptors with some effects on GABA, resulting in nerve excitation paralysis resulting in flea death.

Spinosad is considered to be safe to use in conjunction with all other flea control products and heartworm preventives, but there is one serious drug interaction to be very aware of. When administered to dogs receiving high doses of ivermectin for parasites such as demodicosis, spinosad can increase the risk of neurological ivermectin side effects. Therefore, its use in animals on high dose ivermectin is CONTRAINDICATED. Spinosad does appear safe to administer to animals on low dose ivermectin heartworm preventative, but the owner tries to have owner's administer them several weeks apart to be extra cautious.

Spinosad does not kill other internal or external parasites, and owners need to be educated that it is not a tick preventative. Comfortis® tablets are beef flavored but contain pork protein and hydrolyzed soy, and therefore should not be used in animals on an elimination food trial to evaluate for adverse food reaction. Spinosad is highly effective at killing fleas. It starts working within 30 minutes and has 100% kill rate and typically lasts at least a month. Because of this rapid kill rate, studies done with this product have found that the fleas do not have time to lay eggs before they die, unlike many of the other products.

      ProMeris Duo for Dogs® (metaflumizone with amitraz) - Fort Dodge

Metaflumizone is a novel insecticide that blocks the influx of sodium required to propagate a nerve impulse along the axon and dendrite of the flea neuron. This results in reduced feeding, loss of coordination, paralysis and eventual flea death. Studies have shown excellent flea and flea egg reduction with a high margin of safety. Because the canine product contains amitraz, it should NOT be used in cats (i.e. use the cat product on them!). This addition of amitraz gives protection against ticks, but also means that some thought needs to be given to what owners are dispensed this product. Amitraz is a monoamine oxidase inhibitor (MOI), and, in the author's opinion, the use of it should therefore be avoided if the pet or owner are on a concurrent MOI, such as hydroxyzine, certain antidepressants, antihypertensive medications, and some of the medications used in humans to treat Parkinson's disease. Amitraz can cause hyperglycemia, and its use should be avoided if there is a diabetic in the household, human or animal. Lastly, it is advised to avoid using amitraz products in Chihuahuas, as sudden death has been reported in this breed when dipped with amitraz for the treatment of demodicosis.

This product has been found useful for some dogs in the treatment of demodicosis, and is discussed in the Update on the Treatment of Demodex notes from this conference. Lastly, this product does have a strong odor that some clients find unpleasant, and therefore should be warned about. The author has had multiple patients on this product feel lethargic for 1-2 days after application, and this appears to be a greater issue in the smaller dogs. Lastly, a small subset of dogs treated with this product have developed a pemphigus like skin reaction after application, but this appears to be extremely rare and has been mainly noted in dogs receiving it for demodicosis.

      ProMeris for Cats® (metaflumizone) - Fort Dodge

The cat product is a spot-on application of metaflumizone that does not contain amitraz. Like other flea control products, cats should not be allowed to groom themselves or each other after application. It can cause a temporary localized oily appearance, and clumping of the hair at the application site, which owners may find distasteful. The volume of application is rather large and, again, client education is important. Topical reactions have rarely been reported.

      Vectra 3-D for Dogs® (dinotefuran with permethrin and pyriproxyfen) - Summit Vet Pharm

This product is a monthly spot-on application for flea, tick and mosquito control with the insect growth regulator pyriproxyfen. The permethrin provides tick control and is an excellent repellent, although there is some concern about allowing cats near the dog until the product is dry due to their sensitivity to permethrins. It provides long-lasting repellent activity, and is a fast acting adult flea killer that also provides control for the egg stage of the flea for at least 30 days. Permethrin is added to provide tick control and as an insect repellant. This product is an especially excellent choice for dealing with a patient with mosquito hypersensitivity issues or fly strike.

Vectra for Cats® (dinotefuran, pyriproxyfen) - Summit Vet Pharm This product is similar to the canine product but does not contain permethrin due to aforementioned toxicity concerns.