Selamectin is a topical formulation designed to be applied once per month to stop fleas and a number of other parasites (including heartworm disease) affecting cats and dogs.

Selamectin, the active ingredient in Pfizer's Revolution, is from a group of chemicals known as macrocyclic lactones (MLs), which act on both internal and external parasites.

Other MLs include ivermectin and milbemycin oxime which are commonly used in cats and dogs for heartworm prevention. These chemicals act by interfering with nerve transmission in parasites, causing a flaccid (floppy) paralysis of the parasites and their subsequent death.

Selamectin kills adult fleas and eggs and prevents reproduction. In dogs, Revolution is effective against adult fleas for 30 days, as well as flea eggs. It is also effective in preventing heartworm disease when used monthly. It can be used to treat ear mite infestations and sarcoptic mange as well as controlling infestations of the American Dog tick (Dermacentor variabilis).

In cats, Revolution is effective against adult fleas for 30 days, as well as flea eggs. It is also effective in preventing heartworm disease when used monthly. It can be used to treat ear mite infestations as well as roundworm and hookworm infections.

When Revolution is applied to the skin, it is rapidly transferred around the body. It is absorbed into the bloodstream then re-secreted back onto the skin via the sebaceous glands. These glands serve as a depot and re-secrete the product back onto the skin over the next month.

Selamectin is a very broad spectrum parasiticide with good efficacy against a wide range of internal and external parasites. Trials have demonstrated that more than 98 percent of fleas were killed within 36 hours of application. It controls more than 90 percent of a flea infestation within 30 days of the first dose. Selamectin persists for at least 30 days after dosing.

Revolution causes a 99 percent reduction in flea egg production. Of the small number of surviving eggs, there is a 97 percent reduction in successful hatching, almost eliminating new flea development in treated animals. In cats, a reduction of greater than 90 percent in the number of adults emerging from surviving larvae has been seen in trials, while in dogs, the figure was greater than 96 percent.

As with other topical products, selamectin on hair and dead skin cells is shed from the animal and falls to the ground to kill larvae in the animal's surroundings. A US trial sponsored by Pfizer showed Revolution to be highly effective in inhibiting egg production in adult female fleas.

Revolution is so quickly absorbed that it is safe to bathe pets or take them swimming only two hours after application. No reduction in effectiveness against adult fleas was seen in bathed dogs as opposed to unwashed dogs 30 days after treatment (both 100 percent), Bathed cats actually saw an improvement in effectiveness - 98 percent efficacy in unwashed compared with 99.4 percent in bathed cats!

Revolution is also effective in alleviating the signs of flea allergy dermatitis (FAD). It has been shown to provide flea protection to a suckling litter up to seven weeks of age when the mother is treated with the product, due to the so-called 'umbrella effect'.

Revolution has been demonstrated to be safe the following circumstances:

• in puppies and kittens greater than six weeks of age, given up to 10 times the recommended dose topically
• in heartworm-positive animals, given up to three times (dog) or four times (cat) the recommended dose topically
• in ivermectin-sensitive collies, given three times the recommended dose topically
• in breeding males, given up to three times the recommended dose topically
• in pregnant and nursing females, given up to three times the recommended dose topically
• and in animals, dosed orally with the recommended dose.

Owners should note that oral administration may well induce salivation due to the bitter nature of the product. (Correct dosing of the product is highly recommended, however the above figures demonstrate its high level of safety).

The use of Revolution has occasionally been associated with transient application site reactions such as hair loss, coat color change, and itching. Less than one percent of animals will experience digestive upsets when the product is applied. Occasionally, seizures or muscle twitching have been reported.

Revolution should not be used on sick, debilitated, or underweight animals. It should not be applied to puppies less than six weeks of age or kittens less than eight weeks. It is not recommended that Revolution be applied to heartworm-positive animals.

Revolution is a topical liquid which should be applied to the skin at the base of the neck in front of the shoulder blades. It should only be applied to dry (not wet) animals and they should not be bathed for at least two hours after application. The product should not be massaged into the skin after application.