Frontline and Advantage no longer work on my dogs for flea OR tick prevention, Kiltix did nothing, Advantix did nothing. diatomaceous earth doesn't work, nor does the borax. NOTHING was working on the fleas. Vectra 3D worked on the ticks, but not on fleas. CapStar only works if you give it once a day, so I tried Comfortis. A miracle! NO FLEAS! 30 minutes after they took the pills, everyone stopped scratching! Within 2 days, all the fleas were gone from the dogs, the dog yard, the dog kennels, everything! Finally - relief. I've had no bad side effects thus far - and I've just given them a second dose -according to my vet it actually works for about 6 not 4 weeks. Good thing, too - it's $86.00 per 6 doses. I have 8 dogs - do the math -- ouch!