How is bioavailability defined?

Bioavailability is defined as the proportion of a drug that enters systemic circulation and is available for action at the target site. This measurement is crucial because it determines how much of the administered dose reaches the site of action and thus can exert its therapeutic effects. Factors affecting bioavailability include the drug's formulation, route of administration, and how it is absorbed and distributed within the body.

Understanding bioavailability helps in determining the appropriate dosage and frequency of the drug needed to achieve the desired therapeutic effect while minimizing side effects. It provides a critical insight into the drug's pharmacokinetics, enabling healthcare professionals to make informed decisions regarding the efficacy of a drug in achieving its intended purpose.