Yes, of course, the drug manufacturer makes a difference. A while back physicians caught on and the suggestion is stay with the brand you are on. Right, tell that to the insurance companies and my health fund.
One big thing to watch out for is that while the name brand may have sucrose (plain sugar), many generics use lactose. Cats are usually lactose intolerant and avoiding meds with lactose is a good idea (I'm lactose intolerant so this is a big problem with me). L actose intolerance means nauseau, upset stomach, diarrea.