Draxxin is a long lasting antibiotic, which is why it is so popular among deer breeders. The half-life, how long it takes a drug to be metabolized and eliminated through the liver or kidneys, depending on the particular drug, is what always concerns me about "stacking" antibiotics, giving more than 1 at a time. There are some that work just fine together, and don't cause any serious problems to the eliminating organs, and there are some that "contrindicate" - should never be used together because of the way they react to each other and the damage they can do to the organs. Heavy doses or certain combinations of antibiotics can cause acidosis, or even renal failure. Tetracyclenes and draxxin do not contrindicate, however, when given the option, I like to allow one to clear the kidneys/liver before giving the next, just to reduce the strain on the organ. The residual effect of Draxxin is still effective in terms of fighting infection for several more days (even weeks in some cases), but the initial dose was absorbed, processed and eliminated in the first 24 hours or so.
As for your fawns, like Michael said, Target Fawn Paste as soon as they hit the ground, within the first few hours of life. I also give a C/D antitoxin shot immediately. If you are leaving them on the does, that is about all you can do, since they quickly get uncatchable. If you are bottle raising, obviously you have more control over their health. Let me know if you have specific fawn questions, or had any particular problems last year, and if I can, I'll help.