Sentry Purrscriptions Plus Flea & Tick Squeeze-On for Cats and Kittens is formulated with a revolutionary new adulticide called Etofenprox. Etofenprox has a very low toxicity profile yet it is four times more effective at killing fleas than the other leading OTC brand. Etofenprox when applied monthly kills adult fleas, ticks & repels mosquitoes including the mosquito that carries West Nile virus for up to one month. Also includes nylar, an insect growth regulator that kills flea egg and larvae for up to three months per application. Five Way Strong. Gentle All Month Long!