(1) Always want to start by making sure it was given or applied correctly
(2) If it was then here are 2 scenarios
(a) There is resistance to some topicals, so what are you using?
OR
(b) Your prevention is great and we need to help you target treating your pets environment and the OTHER animals in your pets environment…You are seeing the fleas before they are dying… OTHER PETS… squirrels, rodents, cats around the house outside.