Vitamin B12 Injection Dosage for Adults: 7 Key Facts & Guidelines Liv Hospital like, swipe, and save for when it's your turn to do an injection on a patient Intramuscular (IM) Angle: 90 Needle Size: 2225G, 11.5 inch Med Examples: Vaccines (e.g. Tdap, Ivy Grove Surgery : Self administration of B12 injection Dr. prescribed B12 injections. Pharmacy only gave me vials. Where do you get your needles and syringes? What size?? Where do I inject? : r B12_Deficiency