I know that the new version of Advantage flea meds have been out for a while now, and I have been using them on my dogs and cats without any problems (I actually think they are less effective, but that is a whole different thing!).
For Advantage II, the flea killing ingredients are Imidacloprid and Pyriproxyfen.
For the original (Advantage Multi) the active ingredients are, Imidacloprid and Moxidectin.
So basically my only worry will be the Pyriproxyfen. It is considered a flea growth inhibitor.
For the last, idk, since the new stuff came out, I haven’t been treating the rabbits. They don’t easily get fleas, and their fur is free of fleas as far as I can tell. I figure Nova is more likely to get fleas than Eclipse, since Eclipse has that super dense, short rex fur. So far so good, but spring is just around the corner. Even if weather conditions have been mercifuly unfavorable for fleas so far, that could change, so I want to be prepared now, not later!