What is the term for the process of a drug entering the bloodstream?

The term that describes the process of a drug entering the bloodstream is absorption. This process begins after a drug is administered and involves its movement from the site of administration into the circulatory system. Factors that affect absorption include the formulation of the drug, the method of administration (oral, intravenous, etc.), and the physiological characteristics of the patient, such as gastric pH or blood flow.

In pharmacology, understanding absorption is vital because it directly influences the onset, intensity, and duration of the drug's effects. For instance, intravenous administration allows for immediate absorption since the drug is introduced directly into the bloodstream, whereas oral administration may take longer due to the drug’s absorption through the gastrointestinal tract.

Distribution, metabolism, and excretion are subsequent phases in pharmacokinetics, dealing with how the drug spreads through the body, how it is chemically altered, and how it is eliminated, respectively. These processes occur after absorption and are important for understanding the overall pharmacological action of a drug in the body.