What is the definition of bioavailability in pharmacology?

Bioavailability refers to the proportion of a drug that enters the systemic circulation after it has been administered and subsequently absorbed. This concept is crucial in pharmacology because it impacts the drug's effectiveness and therapeutic outcomes. For instance, a drug that is poorly bioavailable may not achieve adequate plasma concentrations to exert its intended effects.

Understanding bioavailability helps healthcare professionals make informed decisions regarding dosage, route of administration, and therapeutic regimen. While the total amount of a drug delivered to the body and its rate of absorption are important factors in pharmacokinetics, they do not specifically define bioavailability, which focuses on the fraction of the drug that is available to the systemic circulation and therefore, available for action at the site of interest.