Intramuscular injection (IM) refers to an injection (commonly referred to as a shot) which is administered into muscle tissue. As opposed to SC or IP injections, which are administered below the skin (subcutaneous) or into the peritoneum, respectively.
IM injections are generally placed in either the deltoid (shoulder), gluteus (hip) or rectus femoris (thigh). These injection sites are chosen because they represent relatively large muscle which have areas free of major nerves or vessels.
In general, the volume of the injection will determine the choice of muscle. Small injections can be placed in the deltoid. Larger volume injections must be placed into larger muscles. No single IM injection should exceed a volume of 5 ml.
A child's deltoid will be smaller than that of an adult. Thus, a volume which is appropriate for injection into the deltoid of an adult may be better suited to the gluteus of a child.
By choosing a muscle appropriately sized for the volume of the injection, the health care professional can minimize the amount of pain associated with the injection.