Fipronil Spot-On for Dogs is available for 3 sizes of dog, small dogs from 2kgs-10kgs body weight, medium dogs 10kg-20kgs and large dogs 20kgs-40kgs. A further size for extra large dogs over 40kgs will be added if required. Initially, only 1 vial packs have been introduced, being 1 treatment giving up to 8 weeks protection, but larger pack sizes with 3 vials to give 24 weeks protection can be added shortly. Important â€“ to avoid re-infestation (as with all on-animal flea treatments) all cats and dogs in the house must be treated. It is also most important to treat animals baskets, bedding and regular resting areas such as carpets, rugs and soft furnishings with a Household Flea Spray or Room Fogger and vacuumed regularly.