The most common external parasite of cats is the flea. Every outdoor cat will pick up the occasional flea. Given the chance, fleas breed and can build up huge populations indoors. These tend to go unnoticed until the population of fleas has significantly multiplied, which then takes a while to eradicate. The most effective flea treatments available contain fipronil as the active ingredient. Frontline Spot On was the first product like this. Now there are others which work in exactly the same way, such as Fiprospot and Effipro. Frontline and Fiprospot are available in packs of 3 or 6 doses, whereas Effipro comes in packs of 4 or 24 doses and tends to be the most economical product to use. Indorex is our recommended household treatment.