Are you using syringes for IM injections that you have to draw the B12 yourself from a vial?
If you are, I always tighten the needle before removing the cover. As I am turning the needle clockwise to tighten, I gently pull the cap off at the same time. I was taught to draw air into the syringe before inserting it into the vial, then push the air out in the vial, and draw in the B12 slowly. Slowly has been the key for me to keep air out of the syringe. If I do get some air in the syringe, I just hold it needle end pointing up and flick it with my finger until the air rises and push it out of the needle before the injection.
Does that make sense?
Diagnosed with CD in 1979, many resections and meds
Perm Ileostomy July 1984 at Cleveland Clinic
Disease free since surgery