Johnson's 4fleas Tablets for Cats & Kittens Johnson's 4fleas Tablets for Cats & Kittens starts working in 15 minutes & kills fleas in 24 hours. Suitable for cats & kittens over 4 weeks weighing 1-11kg, 4fleas Tablets have no contra-indications & are safe to use with other flea & worm treatments. To kill flea eggs & larvae, use in conjunction with Johnson's 4fleas Spot On Protector for Cats & Kittens.