What It Is
A flea shampoo is a specially medicated shampoo for pets that contains ingredients that kill fleas and/or ticks.
Most commonly a permethrin, or pyrethrin, though ingredients vary by brand.
How it Works
The application of an insecticide in shampoo form offers quick kill off of parasites on the pet. It does not prevent re-infestation from parasites in the environment.
How to Administer
Apply over entire coat, avoiding eyes and mucous membranes. Leave on for specified period of time, generally 10-15 minutes, before thoroughly rinsing.
How Often to Administer
For maximum efficacy, weekly shampoos are recommended.
When properly rinsed, leaves minimal residue to be of concern for pets and children. Even when used as directed, does not provide lasting parasite control compared to spot-on treatments.  Best used in conjunction with other forms of flea control for pets with infestations.
Adams, Hartz, Only Natural Pet
 Comparative efficacy on dogs of a single topical treatment with fipronil/(S)-methoprene or weekly physiological hygiene shampoos against Ctenocephalides felis in a simulated flea-infested environment.
Parasite. May 2012;19(2):153-8.