What term refers to the administration of medication directly into the bloodstream?

The term that refers to the administration of medication directly into the bloodstream is "infusion." Infusion is a method used to deliver drugs, fluids, or electrolytes directly into a patient's bloodstream through a vein, typically using an intravenous (IV) line. This approach allows for immediate therapeutic effects, quick absorption, and precise control of medication dosage.

In contrast, the other options describe different routes of medication delivery. Inhalation refers to administering drugs through the respiratory tract, where medication is inhaled as a gas or aerosol, targeting the lungs. Ingestion involves taking medication orally, where it must pass through the digestive system before entering the bloodstream, which can slow the onset of action. Application usually relates to topical administration, meaning that medication is applied directly onto the skin or mucous membranes, focusing on localized treatment rather than systemic absorption.