How does flea medicine get to the fleas?
September 14, 2021 5:38 PM   Subscribe

Step 1: You squeeze a little mini tube of flea medicine on the back of your cat or dog’s neck. Step 2: ??? Step 3: The adult fleas, larval fleas, or flea eggs laid in your pet’s fur come in contact with the flea medicine and it disrupts a specific protein etc. (details described in the more detailed product information for vets that pet owners can also find on an internet search), so that any flea that comes into contact with the flea medicine for its duration of effectiveness is killed..

The drop on the back of your cat or dog’s neck kills all fleas on the pet, not just the fleas that happen to wander across that spot on their neck. But my vet described it as “non-systemic” (the relevant detail being that it wasn’t going to have any troublesome interactions with the other medications that my cat is on). So how does it get distributed around the cat or dog, thus ensuring that all of the fleas, flea larvae, and flee eggs on the pet are exposed to it and killed? (In case this differs for different flea treatments, I’m specifically curious about Advantage, but also generally curious about all flea treatments with similar application method.)
posted by eviemath to Pets & Animals (6 answers total) 3 users marked this as a favorite
I am not a vet, but as I understand it, it sinks into your pet's pores, and then they sweat it out over a period of time. I'm a little bit scared of the stuff and would appreciate any reassurance anyone has to offer.
posted by jordemort at 6:57 PM on September 14, 2021

Yeah it gets absorbed into the cat and then they’re soaked in flea medication for a month or whatever until you have to redose them because it takes longer than that to get rid of fleas completely. It has worked well for my cats with no apparent side effects.
posted by aubilenon at 7:07 PM on September 14, 2021

Response by poster: I’m not concerned about the safety. I just don’t understand the process! Any guesses for more specific details on that step in between absorbed into the cat and distributed around the cat. Eg. how would it get to pores on other parts of the cat’s body, if fleas are coming into contact with it via pore secretions in Step 3 of my description? My partner thought it got absorbed into the blood and thus distributed by the circulatory system (whose whole job is to distribute stuff around the body, so that would make sense). But that seems like it wouldn’t qualify as “non-systemic”, unless I’m not understanding what systemic versus non-systemic mean as technical medical terms?
posted by eviemath at 7:20 PM on September 14, 2021 [1 favorite]

Best answer: This is a bit of an explanation.

"They don’t absorb through the skin (dermal or hypodermal layers), as they can’t pass the diffusion barrier created by the epidermis’ basal cells (basal lamina). Instead, the compounds remain on the superficial layers of the skin (stratum corneum and epidermis), and collect in the animal’s sebaceous (oil) glands and hair follicles.12

The sebaceous glands and hair follicles act a reservoir for the medicine. It’s slowly and continually secreted through sebum (oil) onto the surface of the skin and hair. The animal’s oils help carry the treatment across the whole body."

I read that as it gets into their oil production glands, and then gradually the oil gets all over their body (presumably via grooming and self-touching, the same way your fingers don't produce oils but they leave fingerprints b/c you touch your face, arms, and other parts that do produce oil).
posted by gideonfrog at 7:30 PM on September 14, 2021 [13 favorites]

Best answer: ^Dermal translocation aka cutaneous distribution.
posted by Iris Gambol at 7:37 PM on September 14, 2021 [5 favorites]

Response by poster: Apparently this does vary by flea medicine! With some (Revolution, perhaps?) getting into the pet’s bloodstream, and thus requiring the fleas to bite before dying (= itchy and uncomfortable for the cat or dog, doesn’t kill flea eggs), while others (eg. the Advantage that my vet recommended) spreading via dermal translocation as described in gideonfrog and Iris Gambol‘s links. (On bringing the other cat, that we found an actual flea on, to the vet yesterday for check-up, vet explained that the flea medicine is actually spread through the fatty layer of the skin itself - so stays in the skin organ (aka non-systemic), but doesn’t rely on chance or brushing or any external surface mechanism for distribution.)
posted by eviemath at 7:40 AM on September 18, 2021

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