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Does Topical Flea Treatment Go Into the Bloodstream?

| Updated September 26, 2017

You know that the topical flea product you put on your pet's skin every month keeps him flea-free. How it works depends on the type of ingredients involved. While some flea control medications enter the bloodstream, others do not. Most topical flea control products are available over the counter, but some require a veterinarian's prescription. This is especially true of those that also contain anthelmintics, or dewormers.

Fipronil Flea Control

Fipronil, marketed under the brand name Frontline, doesn't work primarily by entering the bloodstream, although a minute amount does end up there. Instead, it settles in the animal's sebaceous glands beneath his skin. Once in the glands, Fipronil slowly releases onto the surface of the skin. When fleas come in contact with it, Fipronil disrupts the insect's central nervous system, causing hyperactivity before they succumb. Another ingredient, (S)-methoprene, prevents flea larvae from developing, so no additional fleas appear on your pet while on the medication. The National Pesticide Information Center website reports that researchers applied a high dose of fipronil to the backs of rats. While test samples showed fipronil did appear in the animal's blood, feces and urine, less than 1 percent of the dose was absorbed into the body after 24 hours.

Imidacloprid Flea Control

Imidacloprid, marketed under the brand name Advantage and Advantix, doesn't enter the bloodstream when you put it on your pet's skin. Instead, it spreads throughout the skin, including the sebaceous glands and hair follicles. Imidacloprid is absorbed into the insect's body, poisoning the fleas. It kills off flea larvae in two ways. Larvae either eat contaminated pet dander containing imidacloprid, or they come into direct contact.

Selamectin Flea Control

Selamectin, sold under the brand name Revolution, kills not only fleas but other parasites These include heartworms and roundworms, mites and ticks. Selamectin is available only by prescription. It kills worms by entering the bloodstream, but also stays on the skin. The element remaining on the skin takes care of adult fleas, flea eggs and mites.

Warnings and Considerations

Although certain topical flea products are available over the counter, consult your vet regarding the best type of treatment for your pet. Always follow the directions on the package and give your pet the appropriate dose by weight. Wear gloves when applying topical flea control. Don't use products designed for dogs on cats and vice versa. Package inserts include stickers you can post on your calendar for the next dosage, so you keep your pet up-to-date with protection. Depending on your location, your pet might need seasonal or year-round flea control.