What does the term "bioavailability" refer to in pharmacology?

Bioavailability refers to the proportion of a drug that enters the systemic circulation when introduced into the body and is available for therapeutic effect. This concept is crucial in pharmacology because it helps to determine how much of a drug will be accessible to the targeted tissues or organs after administration.

Factors influencing bioavailability include the route of administration, the drug formulation, and the presence of food or other substances in the gastrointestinal tract. For instance, a drug taken orally undergoes first-pass metabolism in the liver, potentially reducing its bioavailability compared to intravenous administration, where it directly enters the bloodstream.

Understanding bioavailability is essential for pharmacokinetics, as it plays a significant role in determining dosing regimens, efficacy, and safety profiles of medications.