@Iluviaporos - Yeah, you seriously do not want to have an allergic reaction to something that has been injected into you. And it's possible that some people might react to the solution that they dissolve the antibiotics in as well. I know that's true of vaccines anyway.
It makes it more complicated that there are different antibiotic types and people can be allergic to almost any of them. Few people actually ask what kind of antibiotic they are being given, particularly if it is a shot rather than pills.
It's a good idea to keep a list for yourself about the types that you've had so that you know for the future which ones you aren't likely to have a reaction to, in case you get into a situation where that knowledge is crucial.