louisei use a TB syringe for my 3 month old son. however, in an ADULT this would be considered a sub cutaneous injection rather than an intramuscular one. as your child grows, the length and guage (the higher the guage, the SMALLER the needle) will need to be adjusted. the RN at the office should know to tell you when you need to switch from a TB to a typical IM size needle.
louise