Which injection involves administering medication directly into a muscle?

The correct choice involves administering medication directly into a muscle, which is characteristic of an intramuscular injection. This method allows for the medication to be absorbed more quickly into the bloodstream compared to other routes, as muscles have a rich blood supply. Intramuscular injections can accommodate larger volumes of medication, making them suitable for vaccinations and certain therapies that require higher dosages or slower absorption over time. This route is often preferred for medications that may cause irritation if administered subcutaneously or intradermally.

Intradermal injections, administered into the dermal layer of the skin, are typically used for allergy tests or tuberculosis screening and would not deliver medication into a muscle. Intravenous injections involve delivering medication directly into the bloodstream through a vein, allowing for immediate effects but not targeting muscle tissue. Subcutaneous injections involve administering medication into the fatty tissue just beneath the skin, which provides slower absorption and is often used for vaccines and insulin.