air wil not be a problem as long as you don't inject it into a vessell, they teach nursing students a technique called airlock that uses the air in the syringe to trap the meds into the tissue and creat's less ozzing of the meds. the problem with using the outside of the glute is the risk of hitting nerves,like the sciatic and it will hurt like a bitch and may give you problems if when ya introduce the needle into your leg and you feel a sharp pain run down the length of your leg pull it out and start over,later duckster