Not without some specific information as to what the binders/fillers are, and likely some specialized solvents. Stuff like that tends to be tough to remove outside of a proper lab.
Um, not to judge or anything, but why would you want to inject diphenhydramine? That just sounds like a recipe for bad times to me. If you
have to use them and can't/won't take them orally, why not rectally. It will give roughly twice the effect from the same dose, and without much of the risk of injection in general, not to mention all the horrible things that could likely happen from injecting binders, fillers, and other gunk that was designed specifically not to be injected.
Incidentally, questions of this sort will get better visibility over at
Other Drugs. Probably more knowledgeable replies too. Can't guarantee that much of it will be positive though, as what you're talking about sounds like a very bad idea. Good luck!