I had to give our vet tech the lesson as well. She also was horrified when I said I wanted the four pack of over 50lbs for dogs. She knew we had cats! I told her it was the same thing and then she gave me the lecture on how cats and dogs have a very different central nervous system and blah blah blah. Then she read the ingredients on the package and was shocked. They are identical and it is only the dosage that is different. Just for fun she calculated the cost and if I had bought individual dosages it was going to cost me $97.00 but doing the breakdown myself it cost me only $30.00. She gave me two syringes and off we went. I will take that $60.00 savings anyday! A four pack for large dogs gives everyone in my house a dose of Avantage with a few drops to spare!
I'm lucky because my vet sells the tubes for $7.50 so it's cheaper for me to get it from them than to order it.
I have done this for the last few years and thankfully it makes it affordable for me to keep them flea free.