Final answer:
The vastus lateralis muscle, part of the quadriceps group, is the preferred site for intramuscular injections in infants due to its sufficient muscle mass and lower risk of damaging significant structures.
Step-by-step explanation:
The appropriate muscle to administer an intramuscular injection in infants, where the buttocks and arm muscles are underdeveloped, is the quadriceps muscle, specifically the vastus lateralis. This muscle is one of the four components of the quadriceps group located on the anterior thigh. Its lateral position on the thigh makes it easily accessible and large enough for safe injections, which minimizes the risk of damaging nerves or blood vessels that are more prevalent in the gluteus maximus and the deltoid in infants. Moreover, infants have well-developed quadriceps compared to other muscle groups, which facilitates efficient absorption of the medication.
The vastus lateralis is particularly preferred for intramuscular injections in infants due to its sufficient muscle mass and the lower likelihood of encountering important structures that can be damaged with an injection. It is the most commonly used site for vaccinations in infants. When giving an injection in this area, proper technique must be used to ensure medication is delivered into the muscle tissue.