There are dozens of options when it comes to medications that keep dogs safe from disease causing pests...but, how exactly do they do what they do?
How Flea & Tick Spot On Treatments Work
All pet owners do it: we mark our calendars, and each and every month we snap the tip off our trusty flea & tick medication and apply a dab to that one spot on our dogs’ bodies they can’t reach with their mouths. But how does that one little squeeze of liquid
do the trick?
Killing Insects Where They Lay
Insect neurotoxins are the primary active ingredients in most canine flea & tick medication. Insect neurotoxins will stop existing infestations of fleas and ticks by attacking the central nervous systems of bugs. It poisons insects as soon they eat it, but it doesn’t kill them too quickly! It gives infected insects time to return to their evil lair to infect others at the nesting site. These chemicals, in small doses, are harmful to insects but are generally safe for your pet.
The most common insect neurotoxins in dog flea and tick medications are:
Fipronil (FIH-pron-ill), found most commonly in Frontline and PetArmour products.
Imidacloprid (eye-mid-uh-CLOP-rid), found most commonly in K9 Advantix products.
Permethrin (per-METH-rin), also found most commonly in K9 Advantix products, as well as Protical products.
Some other common active ingredients you may come across in topical spot-on treatments may include Etofenprox (in BioSpot products), Selamectin (in Revolution products), Dinotefuran (in Vectra products), and others. Most active ingredients in dog flea and tick spot-ons essentially function the same way.
Banishing Future Generations
Different chemicals do different jobs. The neurotoxins listed above do the dirty work of killing existing infestations, but there are still eggs and larvae to deal with. That’s where Juvenile Hormone Analogs come in. Also known as Insect Growth Regulators (IGRs), these chemicals work to make it impossible for larvae to develop into adulthood, and we can guess what happens when baby insects never make it through buggy puberty - they’re unable to reproduce.
The most common juvenile hormone analogs in dog flea and tick medications are:
Pyriproxyfen (pie-rih-PROX-ifen), found most commonly in K9 Advantix products.
(S)-methoprene (ess-METH-oh-preen), found most commonly in Frontline Plus products.
The “Helping” Ingredients
Synergists are used to enhance the effects of the other ingredients in the medication. If neurotoxins and juvenile hormone analogs are the bullies, synergists have their back.
Two of the most common synergists are:
piperonyl butoxide (pie-per-OH-nil byoo-TOX-eyed)
N-octyl bicycloheptene dicarboximide (enn-OCT-il bye-sih-cloh-HEP-teen die-car-BOX-ih-mide)
Both synergists listed above work to make some “active ingredients” last longer by slowing their chemical degradation. This means the killing chemicals can stick around longer in the metabolism of the insect, which gives fleas and ticks time to get back to their nesting site, thereby bringing the poison home to roost.
How Flea & Tick Oral Tablets Work
may be preferred over spot on flea treatments for a few reasons. Parents of small children, for example, sometimes have to quarantine their dog so babies won’t rub their hands in a recently applied spot on. Physical contact with medicine is not a concern with oral flea tablets.
The most common active ingredients found in dog flea and tick oral medications are:
Spinosad, found in Comfortis Tablets
Nitenpyram, found in Capstar Tablets
Lufenuron, found in Program Tablets
Spinosad works quickly to kill fleas and to prevent future lifecycles, and it lasts a full 30 days. Nitenpyram, conversely, only kills adult fleas and will not prevent future infestations. Nitenpram should be followed up with another oral treatment like Lufenuron, which does not kill adult fleas but does prevent future infestations by rendering eggs and larvae unable to grow and reproduce in much the same way as spot on growth inhibitors.
How Flea & Tick Sprays Work
The active ingredients in flea and tick sprays work in the exact same way as flea and tick spot ons: neurotoxins upset the nervous system of the insects which quickly kills them, and growth inhibitors prevent eggs and larvae from developing in order to prevent future infestations.
The most common active ingredients found in dog flea and tick sprays are:
Fipronil, found in Frontline Spray
(S)-methoprene, found in Zodiac Power Spray
Pyrethrins, also found in Zodiac Power Spray
Special care should be taken when using sprays, as introducing the chemicals into your environment through a spray greatly increases chances of inhalation and physical contact, especially when children are present.
What are “Other," “Inactive” or “Inert Ingredients?"
The actual work-doing medicine in many flea and tick treatments - spot ons, sprays and tablets, may sometimes account for less than 10% of the actual product. The rest - between 15%-90% of the treatment - is other stuff. These ingredients may be classified on the label or box as “other ingredients," “inactive ingredients," or “inert ingredients."
Inert ingredients may serve a variety of functions including extending shelf life, helping a pesticide stick around on your pet’s skin, and keeping the product in its desired state of viscosity or solidity.
The EPA provides a very long list of non-food inert ingredients
that are permitted in products. Any of these could be in any number of flea and tick spot on treatments.
Why aren’t they listed on packages?
Companies aren’t required by law to list their inactive ingredients. Inert Ingredients are protected as trade secrets, or private business information.
* Examples based on ingredients in the leading flea & tick spot on treatments.
More Flea and Tick Control Advice
by Lauren Leonardi
This information is for informational purposes only and is not meant as a substitute for the professional advice of, or diagnosis or treatment by, your veterinarian with respect to your pet. It has, however, been verified by a licensed veterinarian for accuracy.