Hey Davidh, in light of our conversation the other day, and my Vet getting Rocky's vet records in hand, I explained to them i'd rather not use Triflexis, in lieu of Sentinal, lol, and why! The tech said that was fine, but i'll have the vet write a prescription for it, you'll have to go online and fill it, or to another vetā¦.Of course I asked why was that, and she answered the Sentinal was used to stop the fleas from breeding, the Triflexis started killing living fleas within 30 minutes, and so since the Sentinal only controlled birth of new fleas, still allowed flea infestations if you walk your pet outside, but she said she would get the doctor to write the prescription, just didn't feel that it would be useful to Rocky being he was allergic to fleasā¦ā¦. Sensing something more going on than flea control.