Systemic ectoparasite management and the way it works


Remedy and prevention of flea infestations have been a part of the job of companion animal veterinarians for many years. Probably the most vital breakthrough on this space was the invention of efficient topical drugs like fipronil (Frontline) within the Nineties, which put baths and powders on the again of storage cabinets. Since then, many different topicals that work when absorbed by the animal’s pores and skin and sebaceous glands have been developed. However some pet house owners are nonetheless hesitant about utilizing them due to the potential hazard to individuals and different animals. Thus, oral merchandise have been the following main innovation within the administration of fleas.

Earlier than the isoxazoline class of flea/tick preventatives was launched, spinosad (Comfortis, Trifexis) and nitenpyram (Capstar) have been the one oral alternate options to topical flea management. They start killing fleas about half-hour after being administered. Though spinosad is a macrocyclic lactone and nitenpyram a neonicotinoid insecticide, each act on the nicotinic acetylcholine receptors of the flea. When a flea consumes the blood of an animal handled with spinosad or nitenpyram, it ingests the drug, which blocks acetylcholine-mediated neurotransmission, resulting in flea paralysis and dying. All fleas on cats and canine handled with nitenpyram die inside 6 hours; all fleas on cats handled with spinosad die inside 24 hours; and all these on canine equally handled die inside 4 hours.1,2 As a result of these medicine are extra selective for the nicotinic receptors of bugs, the danger of adversarial occasions in canine and feline sufferers is low.

Though the introduction of oral flea management was an enormous win for pets, their dad and mom, and veterinary professionals, the therapy of ticks remained topical. The appearance of prescription-only isoxazolines within the 2010s revolutionized flea and tick administration in canine and cats. All isoxazolines—be they administered orally, as are fluralaner (Bravecto), lotilaner (Credelio), sarolaner (Simparica), and afoxolaner (NexGard) or transdermally, as fluralaner (Bravecto) and sarolaner (Revolution Plus)—are absorbed into the bloodstream of the affected person. And, like spinosad and nitenpyram, they work solely on the neurotransmitter receptors of bugs and arachnids. Fairly than concentrating on nicotinic receptors, isoxazolines goal chloride receptors which might be gated by glutamate and gamma-aminobutyric acid (GABA) and inhibits them on the neuromuscular junction. The selectivity of isoxazolines is considerably larger for insect/arachnid neurons than mammalian neurons. This ends in uncontrolled neuronal exercise within the flea and tick, resulting in paralysis and dying. These medicine bind tightly to plasma proteins, permitting for dosing intervals of 30 days or extra, relying on the product.3-5

Many pet house owners choose oral flea/tick preventatives as a result of there’s nearly no likelihood that an individual or one other pet will get the drug on their pores and skin through contact with the handled animal—a priority I usually hear from dad and mom of younger youngsters. From the attitude of prevention, many within the area hope for elevated proprietor compliance when flavored chewable treatment is prescribed for his or her pet. Oral medicine additionally present an additional benefit in that there isn’t a query they are going to be by chance washed off if the pet is bathed too quickly after administration. Nonetheless, some house owners are extra cautious about drugs that flow into by means of an animal’s physique, preferring these which might be restricted to the pores and skin. Though uncommon, the adversarial results of isoxazolines may be vital. All include boxed warnings in regards to the threat of such adversarial occasions as seizures, tremors, and ataxia. The warning additionally recommends exercising warning when prescribing to sufferers with a historical past of seizures and notes that isoxazolines could cause seizures even in sufferers with no identified historical past of seizures.4 In my expertise, discontinuing an isoxazoline that precipitated a seizure is healing. Extra widespread unwanted side effects are vomiting, diarrhea, lethargy, and inappetence.3,5

Along with killing fleas and ticks, isoxazolines are an efficient off-label therapy for cutaneous myiasis (pores and skin infestation by the larvae of sure fly species) and for a lot of different ectoparasites, together with Demodex, Sarcoptes, and Otodectes mites, suckling lice, Psoroptes cuniculi (rabbit ear mite), and Triatoma (the vectors of Chagas illness).4 Particularly with regard to Demodex and Sarcoptes, isoxazolines are far more practical, safer, and simpler for pet house owners to handle than ivermectin.

Though extremely efficient at killing fleas, ticks, and different ectoparasites, the primary downside of isoxazolines—aside from a uncommon threat of seizure— is that they don’t repel ectoparasites. Given their fast pace of kill (8 hours for fleas and 12 hours for ticks with fluralaner in canine, for instance3), most sufferers is not going to be uncovered to the parasites for a major time frame. Nonetheless, sufferers with flea allergy dermatitis (FAD) and people uncovered to a heavy tick burden could profit from concurrent therapy with a topical preventative that each repels and kills, thus offers 2 layers of protection in opposition to fleas and ticks.

Isoxazolines kill ticks and fleas usually earlier than they’ve the possibility to trigger illness. Nonetheless, each affected person (and pet proprietor) is a person, and never all sufferers are candidates for an isoxazoline. Seizures should be mentioned with house owners earlier than these medicine are prescribed to grownup animals. If scientific indicators of FAD are current or if routine tickborne illness antibody testing is constructive when utilizing solely an isooxazoline drug, clinicians should focus on compliance and the choice of including or altering preventative drugs with pet house owners.

Jeffrey Haymaker, VMD is an affiliate veterinarian at Mount Laurel Animal Hospital and 24-hour Emergency Service in New Jersey. His veterinary pursuits embody inner medication and surgical procedure. He works within the major care division in addition to within the emergency service. Haymaker is a member of the American Veterinary Medical Affiliation and is the treasurer of the Southern New Jersey Veterinary Medical Affiliation. He’s additionally an adjunct teacher of veterinary expertise at Manor Faculty in Jenkintown, Pennsylvania.


  1. CAPSTAR – Nitenpyram Pill. US Product Label. Elanco US Inc; 2020.
  2. COMFORTIS – Spinosad Pill, Chewable. US Product Label for Canine and Cats. Elanco US Inc; 2018.
  3. BRAVECTO – fluralaner pill, chewable for canine. US product label. Merck Animal Well being; 2019.
  4. Plumb, D. Medical Choice Help for Veterinary Groups. Plumb’s Veterinary Medication. Accessed August 3, 2022.
  5. SIMPARICA CHEWABLES – Sarolaner Pill, Chewable. US Product Label. Zoetis Inc; 2017.

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