How I Treat Flea Allergy Dermatitis in 2008
World Small Animal Veterinary Association World Congress Proceedings, 2008
Peter J. Ihrke, VMD, DACVD
Department of Medicine, School of Veterinary Medicine, University of California, Davis
Davis, CA, USA


Flea allergy dermatitis (FAD) is not only the most common skin disease seen in small animal practice in most countries in the world; it is the most common disease of any organ system seen in small animal practice worldwide. Globally, the most common allergic canine skin diseases are, in frequency of occurrence, flea allergy dermatitis, atopic dermatitis, and food allergy (adverse reactions to food).

Reasons for Flea Allergy Dermatitis Treatment Failure

1.  Failure to treat all in-contact animals ('the squeaky wheel gets the oil...'), in-and-out cats, regular animal visitors

2.  Failure to use flea products properly with consistency

3.  Substitution of over-the counter (OTC) spot-on products

4.  Failure to deal with environmental issues in severe cases

Lessons From Flea Biology and Flea Hypersensitivity

The cat flea is the primary flea species in dogs and cats. Adult fleas begin feeding (injecting antigen) almost immediately after finding a host. Formerly, FAD was viewed as an 'all-or-none phenomenon'. Companies advertised with the myth that products 'killed the fleas before they can bite'. Studies have shown that most fleas feed within 5 minutes on the host before most modern products kill fleas. Therefore, effective modern products must diminish rather than prevent flea feeding. Flea allergy is now recognized as another dose dependent hypersensitivity contingent on the antigen dosage injected. The severity of FAD is dependent on allergy severity, number of fleas feeding, and amount of antigen injected. Products with rapid kill should diminish FAD more effectively!

Historically, flea control has required treating both the animal and the environment. Today, more rapid acting and more effective topical and systemic anti-flea therapy may be the only management required. The initial agents that created this paradigm shift include imidacloprid, fipronil, selamectin, nitenpyram, lufenuron, S-methoprene, and pyriproxifen. Despite relatively rapid flea kill and industry claims, none of these products prevent fleas from feeding before they are killed. However, these products reduce an animal's flea burden enough to diminish clinical signs of FAD. New oral product containing spinosad and topical products containing dinotefuran and metaflumizone may substantially add to that armamentarium.

Modern Flea Control

Many insecticides can effectively kill fleas; preventing reinfestation is the problem. Ensuring long-term pet owner compliance also is required. Insecticides and insect growth regulators with novel dosage forms (spot-ons and oral systemic products) coupled with prolonged residual activity has dramatically improved owner compliance and prevented reinfestations. Although insecticidal resistance most often is suspected when flea control measures have failed, lack of control more often results from lack of understanding of flea biology.

The goals of flea control should be elimination of existing fleas, continued elimination of fleas from the premises, and prevention of reinfestation. In order to accomplish this, an integrated flea control plan must be instituted. Residual adulticides must be used to kill fleas plus provide residual killing activity.

Modern Flea Control Products

New spot-on veterinary products display superior efficacy, safety, and residual activity. These products need to be applied directly to the skin. Our strong clinical impression is that dogs and cats with flea allergy experience better efficacy when these products are applied every 3 weeks instead of monthly. Our strong clinical impression also is that either bathing or swimming degrades the efficacy of all spot-on topical products. Over-the-counter (OTC) products do not have the efficacy, residual activity, or the safety of the veterinary products. More recently, safe and effective oral veterinary products offering rapid kill have become available.


Spot on preparation (Advantage®, Bayer)

 Advantages--larvicidal on the animal and kills/debilitates adult fleas on contact, ease of application

 Disadvantages--does not have repellent action, diminished efficacy after bathing or swimming, does not have activity against ticks, occasional application site reactions

 Bottom-line--good narrow-spectrum product for fleas

(Canada--Imidacloprid & Moxidectin--Advantage Multi®, Bayer, Europe--Imidacloprid & Moxidectin--Advocate®)

Fipronil & S-Methoprene

Spot on & spray (Frontline® Plus, Merial), Fipronil (Frontline® Spray, Merial)

 Advantages--kills adult fleas, disrupts flea life cycle, ease of application, kills ticks, spray--rapid dispersion and coverage

 Disadvantages--does not have repellent action, diminished efficacy after bathing or swimming, occasional application site reactions, spray is more effective but labor-intensive

 Bottom-line--good broader spectrum product

Imidacloprid & 44% Permethrin

Spot on preparation (Advantix®, Bayer)

 Advantages--larvicidal on the animal, kills or debilitates adult fleas on contact, interrupts flea life cycle, repellent 'flushing' permethrin, ease of application, also kills ticks and mosquitoes

 Disadvantages--dog only product, diminished efficacy after bathing/swimming, occasional application site reactions

 Bottom-line--good broader spectrum product, dog only


Spot on preparation (Revolution® [USA]; Stronghold® [Europe], Pfizer)

 Advantages--broad spectrum against many parasites, kills adult fleas plus larvae and eggs, rapid flea kill in cats, kills ticks, kills mites (Sarcoptes, Notoedres, Cheyletiella, Otodectes), ease of application, better product in cats?

 Disadvantages--no repellent action, diminished efficacy after bathing or swimming, slower efficacy on dogs?, application site reactions

 Bottom-line--good broader spectrum product


Oral tablet (CapstarTM, Novartis)

 Advantages--rapid response with visual results, kills all adult fleas within 6 hours, short-acting, oral administration, give every 24-72 hours, very safe

 Disadvantages--no repellent action, does not disrupt flea life cycle, short-acting, does not have activity against ticks, expensive when used frequently

 Bottom-line--good narrow spectrum product, use with spot-ons initially for rapid response, use in dogs requiring frequent shampooing or that swim


Oral tablet (Program®, Novartis; Sentinel® [lufenuron + milbemycin oxime])

 Advantages--oral product, very safe, adverse reactions not seen

 Disadvantages--does not kill adult fleas or pupa, time lag 60-90 days to disrupt flea life cycle, no repellent action, no activity against ticks, give with food

 Bottom-line--use with spot-ons or newer oral products, not for use as sole therapy unless closed environment, treat all animals, use in dogs requiring frequent shampooing or that swim


Oral chewable tablet (Comfortis®, Lilly). New oral monthly beef-flavored tablet for dogs, activates nicotinic acetylcholine receptors

 Advantages--rapid response for a systemic once monthly product, kills adult fleas before egg laying initiated, efficacy not affected by bathing or swimming

 Disadvantages--no perceived disadvantages yet

 Bottom-line--awaiting judgment, exciting potential!

Dinotefuran, Permethrin & Pyriproxifen

(Vectra 3D®, Summit VetPharm). New neonicotinoid insecticide.

 Advantages--fast-acting monthly topical

 Disadvantages--dog only product, do not use on cats, assume diminished efficacy after bathing or swimming, occasional application site reactions?

 Bottom-line--awaiting judgment, exciting potential!

Metaflumizone Spot On Preparation

(ProMerisTM for cats, Fort Dodge). New product.

 Advantages--kills/debilitates adult fleas on contact, ease of application, stops egg production?

 Disadvantages--no repellent action, assume diminished efficacy after bathing or swimming, no activity against ticks, occasional application site reactions?

 Bottom-line--awaiting judgment

Metaflumizone & Metaflumizone & Amitraz

Spot on preparation (ProMerisTM for dogs, ProMerisTM for cats, Fort Dodge). New product.

 Advantages--kills/debilitates adult fleas on contact, ease of application, stops egg production?, efficacy against ticks

 Disadvantages--separate dog & cat products, no repellent action, diminished efficacy after bathing or swimming?, occasional application site reactions?

 Bottom-line--new product awaiting judgment


Spot on preparation (PracTicTM, Novartis Europe)

 Advantages--kills adult fleas on contact, ease of application, efficacy against ticks

 Disadvantages--no repellent action, diminished efficacy after bathing/swimming?

 Bottom-line--awaiting judgment

Personal Recommendations

1.  Client education is crucial. All dogs and cats in the environment must be treated.

2.  Flea control must be personalized and regionalized based on severity of possible infestation in your locale, number of dogs and cats in the environment, indoor/outdoor/run free status, infested pests and strays in the environment, finances of the owner, and severity of disease vs. magnitude of the infestation.

3.  Indoor only dogs or cats with very limited possible flea exposure--lufenuron plus or minus spot-on product, spinosad monthly, nitenpyram every few days.

4.  'The average dog'--fipronil & S-methoprene, imidacloprid, imidacloprid & permethrin, selamectin, spinosad, dinotefuran with permethrin & pyriproxifen.

5.  'The average cat'--selamectin, fipronil & S-methoprene, or imidacloprid as sole therapy.

6.  Dogs that swim--nitenpyram every 1-2 days, spinosad monthly.

7.  Dogs requiring bathing regularly--nitenpyram every 1-2 days, spinosad monthly.

8.  Severely flea allergic dogs--more aggressive therapy--imidacloprid plus permethrin, fipronil & S-methoprene plus nitenpyram, spinosad only?

9.  Severely flea allergic cats--more aggressive therapy--selamectin, fipronil & S-methoprene, or imidacloprid plus nitenpyram.

Speaker Information
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Peter J Ihrke, VMD, DACVD
School of Veterinary Medicine
University of California
Davis, California, USA

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