Flea medication for dogs comes in a variety of forms: powders, sprays, lotions and collars, as well as shampoos, drops and oral medications. Each of these forms of flea medication for dogs provides either treatment for an infestation, prevention or both. Drugs such as pyrethins and pyrethroids, imidacloprid, arylheterocycles, metaflumizone and insect growth regulators are available in various forms. Other flea medications for dogs that are available in various forms include selamectin, nitenpyram, spinosad and more natural flea treatments such as citrus extracts and borate.
Pyrethins are one of the most commonly used ingredients in flea medication for dogs. They are extracted from the flowers of chrysanthemum plants and have been in use as an effective flea treatment for more than a century. This extract chemically alters the nervous system cells of insects, including fleas, ticks, lice and mosquitoes. Most flea and tick treatment medications that contain pyrethins are applied directly on the pet, such as a powder or spray.
Pyrethroids are synthetic pyrethrins formulated in a laboratory. As with pyrethrins, pyrethroids irritate and fatally alter the nervous systems of fleas and ticks. Pyrethroids work more slowly than pyrethrins but provide more sustained effects, so pyrethroids are used in sprays and oil-based flea medication for dogs. These medications are harmful to cats and might cause temporary toxicity poisoning in sensitive dogs.
Most flea medication for dogs work to alter the insects' nervous systems. Imidacloprid, a topical insecticide oil applied monthly, blocks nerve receptors. Arylheterocycles and metaflumizone drugs cause paralysis in fleas. Nitenpyram is a safe oral product but its effectiveness is very short-lived because the drug usually is flushed from the pet's system in about 24 hours. Spinosad, another oral product, typically is effective only against adult fleas.
Selamectin is a very potent drug used for controlling fleas, ticks, intestinal parasites, ear mites and heartworm disease. Applied topically, selamectin is absorbed into the animal's bloodstream and gastrointestinal tract, and it kills nearly all fleas within 36 hours of application. Selamectin is known to be safe for pregnant and nursing females, breeding dogs and collies, but it should not be given to young animals that are younger than six weeks old or to sick or weak animals.
Insect development inhibitors (IDIs) and insect growth regulators (IGRs) prevent the growth of fleas. IDIs inhibit the development of chitin, a substance necessary for adulthood. IGRs use the juvenile growth hormone to prevent the flea from maturing. IDIs and IGRs do not kill fleas and usually are combined with an additional insecticide. These chemicals are commonly used in foggers or sprayers or as oral medications or topical sprays.
Some of these drugs have a high toxicity, so natural flea repellents are on the rise. Citrus extracts can be added to dips, shampoos and sprays, and like other insecticides, they affect the fleas' nervous systems. Some dogs might be highly sensitive to citrus extracts. Borate, often in the form of borax powder, inhibits insect growth, but its long-term effects are unknown and it has been found to be less safe than IGRs and IDIs.