Pharmacokinetics and Biopharmaceutics Flashcards

Which pharmacokinetic parameter represents the time required for the plasma drug concentration to decrease by 50%?

Answer: Elimination half-life

Elimination half-life (t½) is the time required for the plasma concentration of a drug to fall by 50%, making it the parameter that directly describes elimination rate.

What is the bioavailability of a drug administered intravenously?

Answer: 100%

IV administration delivers the drug directly into systemic circulation, bypassing all absorption barriers and resulting in 100% bioavailability by definition.

Which pharmacokinetic process describes the reversible transfer of a drug from the bloodstream into body tissues and organs?

Answer: Distribution

Distribution is the reversible transfer of drug from the bloodstream into body tissues, determined by factors such as lipophilicity, protein binding, and tissue blood flow.

Volume of distribution (Vd) is BEST described as:

Answer: A hypothetical volume relating total drug in the body to plasma concentration

Volume of distribution is a hypothetical (not anatomical) volume representing the ratio of the total amount of drug in the body to its plasma concentration.

Which factors PRIMARILY determine the rate of drug absorption from the gastrointestinal tract?

Answer: Drug lipophilicity and dissolution rate

Drug lipophilicity (fat solubility) and dissolution rate are the primary determinants of GI absorption rate, as they govern how readily a drug crosses intestinal membranes.

First-pass metabolism is BEST defined as:

Answer: Drug metabolism in the liver before the drug reaches systemic circulation

First-pass metabolism occurs when a drug absorbed from the GI tract is metabolized by the liver before reaching systemic circulation, significantly reducing oral bioavailability.

For a drug with a HIGH hepatic extraction ratio administered orally, which factor MOST significantly affects its systemic exposure?

Answer: Changes in hepatic blood flow

For high-extraction drugs, hepatic blood flow is the rate-limiting factor for clearance; even small changes in liver perfusion substantially alter drug exposure.