Bioavailability is defined as which of the following?

Bioavailability is defined as which of the following?

• A. The fraction of unchanged drug reaching the systemic circulation following administration
• B. The rate of drug excretion from the body
• C. The fraction of the drug that is eliminated unchanged
• D. The extent to which a drug is distributed to target tissues

Answer: (A)

Bioavailability describes the fraction of the administered dose that reaches the systemic circulation in an active (unchanged) form. This is the key measure of how much drug is actually available to produce an effect, regardless of how the body processes or distributes it after absorption. For intravenous dosing, bioavailability is 100% since the drug goes directly into circulation; for other routes, it’s less due to incomplete absorption and first-pass metabolism. The concept is typically quantified by comparing the area under the concentration–time curve (AUC) after non-intravenous dosing to the AUC after IV dosing, adjusting for dose. The other ideas describe clearance (rate of excretion), elimination, or distribution to tissues, which are separate pharmacokinetic concepts.

Bioavailability describes the fraction of the administered dose that reaches the systemic circulation in an active (unchanged) form. This is the key measure of how much drug is actually available to produce an effect, regardless of how the body processes or distributes it after absorption. For intravenous dosing, bioavailability is 100% since the drug goes directly into circulation; for other routes, it’s less due to incomplete absorption and first-pass metabolism. The concept is typically quantified by comparing the area under the concentration–time curve (AUC) after non-intravenous dosing to the AUC after IV dosing, adjusting for dose. The other ideas describe clearance (rate of excretion), elimination, or distribution to tissues, which are separate pharmacokinetic concepts.