What does the term "bioavailability" refer to?

The term "bioavailability" specifically refers to the proportion of a drug that reaches systemic circulation unchanged after administration. This measurement is crucial in pharmacology, as it directly affects the drug's therapeutic efficacy.

For example, if a drug is administered orally, various factors such as the route of administration, formulation, and the presence of food can influence how much of the drug is absorbed into the bloodstream and is available for the body to utilize. Bioavailability is often expressed as a percentage.

Understanding bioavailability helps healthcare professionals determine the correct dosage and administration route to ensure that the drug achieves its desired effect in the body. This concept is fundamental when comparing different delivery methods, such as oral versus intravenous administration, as intravenous administration typically has a bioavailability of nearly 100%, while oral routes may vary widely due to first-pass metabolism and other factors.

This definition differentiates bioavailability from other pharmaceutical concepts, such as the complete absorption of a drug, which is not always the case, as some of the drug could be metabolized before reaching systemic circulation. Bioavailability does not refer to the effectiveness of a drug post-metabolism or the incidence of side effects, which are separate considerations in pharmacology.