Which process describes the absorption of a drug into the systemic circulation?

The absorption of a drug into systemic circulation is best described by the term bioavailability. Bioavailability refers to the proportion of an administered dose of a drug that reaches the systemic circulation intact and is available for therapeutic action. It accounts for both the extent of absorption and the rate at which the active drug reaches the bloodstream after administration.

When a drug is administered, it undergoes several processes before it can exert its effects. The process of absorption involves the movement of the drug from its site of administration into the bloodstream. Factors influencing bioavailability include the route of administration (e.g., oral, intravenous, intramuscular), the drug formulation, and individual patient factors, all of which can alter how much of the drug actually enters systemic circulation.

In contrast, distribution, elimination, and metabolism describe different phases of pharmacokinetics. Distribution refers to the dispersion of the drug throughout the body's fluids and tissues after it has entered circulation. Elimination encompasses the processes by which the drug is removed from the body, typically through the kidneys or liver. Metabolism involves the biochemical modification of the drug, usually in the liver, which can lead to either activation or deactivation of the drug. Thus, while important, these processes do not specifically pertain to the absorption