Where is the preferred intramuscular injection site for vitamin K in a newborn?

• A. Gluteal muscle
• B. Deltoid muscle
• C. Rectus femoris muscle
• D. Vastus lateralis muscle

Answer: (A)

The important idea here is choosing a safe, reliable intramuscular site for a newborn. In newborns, the anterolateral portion of the thigh, specifically the vastus lateralis muscle, is the preferred site for injections like vitamin K. This muscle provides a sizable, well-developed area with good absorption and is away from major nerves and vessels, reducing the risk of injury to structures such as the sciatic nerve. In contrast, the buttocks (gluteal region) are not favored in newborns because the gluteal muscles are small and injections there carry a higher risk of nerve injury and inconsistent absorption. The deltoid is too small for a newborn, making administration unreliable and potentially painful. While other thigh muscles exist, the vastus lateralis remains the standard due to safety and predictability.