Is there a veterinarian in the house? US sick puppies got a question.
It really depends on the sterile technique used initially. If its a clean product (ie pharmaceutical grade as an example) that you use alcohol on the stopper before and after you draw it up, with a new/sterile needle and syringe, the risk is minimal. If its anything else, there is a risk. That risk goes up exponentially depending on the manufacturing methods used for a given drug. Remember, most injectable drugs with long shelf lifes have some form of bacteriostatic agent in them.
You could always consider trying to filter the bottle with a micron filter, but thats not fullproof and if you use a dirty filter/needle/syringe it could contaminate things even more.
Boiling it will probably ruin it.
