What type of injection is classified as a form of systemic drug delivery?

The correct choice, subcutaneous injection, is considered a form of systemic drug delivery because it allows the medication to be absorbed directly into the bloodstream. When a drug is delivered subcutaneously, it is injected into the layer of fat and connective tissue beneath the skin. This method enables the drug to slowly enter systemic circulation, providing a prolonged therapeutic effect.

Other methods of injection, such as intravenous and intramuscular routes, do deliver drugs into systemic circulation as well, but they are typically not categorized under the same classification as subcutaneous injections in certain contexts. Intravenous injections provide immediate access to the bloodstream, making them suitable for situations requiring rapid drug action. Intramuscular injections can also deliver medications systemically, but the absorption rate can vary depending on the muscle's blood supply and the formulation of the drug. Topical administration, on the other hand, does not deliver medications systemically; instead, it is designed for localized effects on the skin or mucous membranes.