Which route requires the smallest injection volume?

• A. Intravenous
• B. Intradermal
• C. Intramuscular
• D. Subcutaneous

Answer: (B)

Injection volume is limited by the capacity of the tissue space you’re injecting into. The intradermal space, which is the dermis just beneath the epidermis, is very small and holds only a tiny amount of fluid. Because of that limited space, intradermal injections use very small volumes—typically about 0.1 mL or less—to form a small bleb and keep the liquid confined to the dermis for the desired local effect. Injecting more would push the fluid into deeper tissues or spread out, causing more pain and reducing the intended local immune response.

In contrast, intramuscular and subcutaneous tissues have greater capacity to hold larger volumes, and intravenous administration bypasses tissue space altogether by delivering directly into the bloodstream, where the notion of a “small space” isn’t the same. So the route that requires the smallest injection volume is intradermal.