Where should you administer an epinephrine auto-injector on the body?

• A. Upper arm
• B. Buttocks
• C. Middle third of outer thigh
• D. Calf

Answer: (C)

Epinephrine auto-injectors are designed to deliver the medication into a large, well‑perfused muscle for rapid absorption into the bloodstream. The middle third of the outer thigh targets the vastus lateralis, a thick muscle that provides reliable intramuscular absorption and is easy to access quickly, even through clothing. This site also minimizes the chance of hitting nerves or blood vessels and avoids slower absorption in fatty tissue. Other locations are less reliable: the calf has less predictable muscle mass, the upper arm can be harder to reach quickly and absorb consistently, and the buttocks contain more subcutaneous fat which slows uptake. So, the middle third of the outer thigh is the best site for prompt, effective delivery.