KAPS Pharmacokinetics and Biopharmaceutics 1 — Questions and Answers
Question 1: Which pharmacokinetic parameter represents the time required for the plasma drug concentration to decrease by 50%?
- Volume of distribution
- Elimination half-life (Correct answer)
- Bioavailability
- Protein binding fraction
Correct 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.
Question 2: What is the bioavailability of a drug administered intravenously?
- 50%
- 75%
- 90%
- 100% (Correct answer)
Correct answer: 100%
IV administration delivers the drug directly into systemic circulation, bypassing all absorption barriers and resulting in 100% bioavailability by definition.
Question 3: Which pharmacokinetic process describes the reversible transfer of a drug from the bloodstream into body tissues and organs?
- Absorption
- Distribution (Correct answer)
- Metabolism
- Excretion
Correct 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.
Question 4: Volume of distribution (Vd) is BEST described as:
- The actual plasma volume in the body (approximately 3 L)
- A hypothetical volume relating total drug in the body to plasma concentration (Correct answer)
- The total body water volume (approximately 42 L)
- The volume of urine produced per day
Correct 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.
Question 5: Which factors PRIMARILY determine the rate of drug absorption from the gastrointestinal tract?
- Drug molecular weight alone
- Drug lipophilicity and dissolution rate (Correct answer)
- Plasma protein binding capacity
- Hepatic blood flow
Correct 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.
Question 6: First-pass metabolism is BEST defined as:
- The initial phase of renal drug elimination
- Drug metabolism in the liver before the drug reaches systemic circulation (Correct answer)
- The first metabolic step occurring in plasma proteins
- Drug breakdown by stomach acid
Correct 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.
Question 7: For a drug with a HIGH hepatic extraction ratio administered orally, which factor MOST significantly affects its systemic exposure?
- Changes in renal blood flow
- Changes in hepatic blood flow (Correct answer)
- Changes in plasma protein binding
- Changes in gastric pH
Correct 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.
KAPS Pharmacokinetics and Biopharmaceutics 1
Which pharmacokinetic parameter represents the time required for the plasma drug concentration to decrease by 50%?