Johnson's Fipronil Spot-on for Cats Johnson's Fipronil Spot-on for Cats is flea & tick treatment for cats & kittens over 8 weeks of age & weighing more than 1kg. Johnson's Fipronil Spot-on for Cats contains Fipronil, the same active ingredient as Frontline. Fipronil is an insecticide/acaricide (pesticide) in the phenylpyrazole family which gets to work straight away & is effective against fleas (Ctenocephalides felis) for up to 5 weeks & kills ticks within 48 hours. Johnson's Fipronil Spot-on for Cats does not prevent ticks from attaching to the animals, but if the animal has been treated prior to exposure to the ticks, the ticks will start to be killed in the first 24-48 hours after attachment. This is usually prior to engorgement, thus minimising the risk of transmission of diseases. Once dead, ticks will often drop off the animal & any remaining ticks may be easily removed by a gentle pull. To treat a flea infestation, all cats & dogs should be treated with a suitable flea treatment at the same time. You should also treat the pet's basket, bedding & any carpets & soft furnishings that it comes into contact with, using a suitable insecticide (such as a household flea spray) & vacuum these areas regularly.