What is the appropriate site for administering an IM injection of diphtheria-tetanus with pertussis (DTaP) to a 4-month old infant?

For administering an intramuscular (IM) injection of diphtheria-tetanus with pertussis (DTaP) in a 4-month-old infant, the appropriate site is the vastus lateralis. This muscle is located on the outer thigh and is commonly used for IM injections in infants due to its size and depth, making it a safe and effective site for medication administration.

At this age, infants have not yet developed sufficient muscle mass in the deltoid, which makes it less suitable for IM injections. Furthermore, the ventrogluteal site is generally recommended for older children and adults, as it can be difficult to locate accurately in infants. The subcutaneous route is not ideal for DTaP, as the vaccine is designed to be delivered deep into the muscle to promote a proper immune response.

Using the vastus lateralis allows for proper absorption of the vaccine and minimizes the risk of injury or complications, making it the recommended site for immunizations in young children.