Final answer:
For a 1-year-old child, the vastus lateralis muscle on the lateral aspect of the thigh is the best site for an intramuscular injection due to its large size and low risk of harming nearby blood vessels and nerves.
Step-by-step explanation:
When administering an intramuscular injection to a 1-year-old child, it is essential to select a muscle that is well developed and can tolerate the volume of the vaccine or medication to be administered. One of the preferred sites for intramuscular injections in infants and young children is the vastus lateralis muscle. This muscle is one of the quadriceps muscles on the lateral side of the thigh, and it is a good choice because it is large enough to accommodate the injection and is not near major blood vessels and nerves that could be damaged.
In contrast, the deltoid muscle, while commonly used for injections in older children and adults, is generally not developed enough in young children to be used safely. The dorso gluteal muscle, found in the buttocks, was once a common site for injections but is no longer recommended in children and infants because of the risk of injury to the sciatic nerve. The gastrocnemius muscle, in the calf, is also not recommended for intramuscular injections due to its proximity to nerves and blood vessels.
Therefore, the final answer to the original question about the best location to administer an intramuscular injection to a 1-year-old child is the vastus lateralis muscle, thanks to its size and safety profile for this age group.