What You Never Knew About Bioavailability in Pharmacology
#bioavailability (F) is the fraction of an administered dose of a drug that reaches the systemic circulation in an unchanged form. When a drug is given #intravenously (IV), bioavailability is 100% because the drug directly enters the #bloodstream without needing to be absorbed or undergoing #first-pass metabolism. For orally administered drugs (PO), bioavailability is typically less than 100% due to factors like incomplete absorption and first-pass metabolism.
Understanding Bioavailability through Area Under the Curve (AUC)
The area under the curve (AUC) on a plasma concentration versus time graph represents the total drug exposure over time, which allows clinicians to calculate bioavailability. For example:
AUC IV (horizontally striped area): Indicates the AUC for an IV dose, typically providing 100% bioavailability.
AUC PO (vertically striped area): Indicates the AUC for an oral dose, which is often less than 100% due to the drug’s incomplete absorption and first-pass effect.