Bioavailability for routes of administration is defined as

Bioavailability for routes of administration is defined as

• A. The rate of drug absorption
• B. The fraction of an administered dose that reaches systemic circulation
• C. The amount of drug that binds to plasma proteins
• D. The rate of elimination

Answer: (B)

Bioavailability describes how much of the administered drug actually makes it into the bloodstream in active form. It’s the fraction of the dose that reaches systemic circulation, capturing both absorption and any loss to first-pass metabolism before it arrives. For an intravenous dose, bioavailability is 100% because it goes directly into circulation. With other routes, it’s typically less than 1 due to incomplete absorption and hepatic or intestinal first-pass metabolism. The rate at which the drug enters the blood (absorption rate) is separate and influences how quickly effects begin, not the total amount that ultimately reaches circulation. Binding to plasma proteins or the rate of elimination affects distribution and duration, not the fraction that reaches systemic circulation. Hence, the definition is the fraction of the administered dose that reaches systemic circulation.

Bioavailability describes how much of the administered drug actually makes it into the bloodstream in active form. It’s the fraction of the dose that reaches systemic circulation, capturing both absorption and any loss to first-pass metabolism before it arrives. For an intravenous dose, bioavailability is 100% because it goes directly into circulation. With other routes, it’s typically less than 1 due to incomplete absorption and hepatic or intestinal first-pass metabolism. The rate at which the drug enters the blood (absorption rate) is separate and influences how quickly effects begin, not the total amount that ultimately reaches circulation. Binding to plasma proteins or the rate of elimination affects distribution and duration, not the fraction that reaches systemic circulation. Hence, the definition is the fraction of the administered dose that reaches systemic circulation.