Pharmacy Pharmacokinetics 1 — Questions and Answers
Question 1: What does 'bioavailability' refer to in pharmacokinetics?
- The rate at which a drug is metabolized by the liver
- The fraction of an administered dose that reaches systemic circulation unchanged (Correct answer)
- The volume of plasma cleared of drug per unit time
- The time required for drug concentration to decrease by half
Correct answer: The fraction of an administered dose that reaches systemic circulation unchanged
Bioavailability is the fraction (F) of an administered dose that reaches the systemic circulation in unchanged form, making it available for therapeutic effect.
Question 2: Which route of administration achieves 100% bioavailability?
- Oral
- Sublingual
- Intravenous (Correct answer)
- Transdermal
Correct answer: Intravenous
Intravenous (IV) administration delivers drug directly into systemic circulation, bypassing all absorption barriers, and is the reference standard for 100% bioavailability.
Question 3: The 'first-pass effect' primarily occurs in which organ?
- Kidney
- Lung
- Liver (Correct answer)
- Small intestine only
Correct answer: Liver
The first-pass effect (presystemic metabolism) primarily occurs in the liver, where orally absorbed drugs are extensively metabolized before reaching systemic circulation, significantly reducing bioavailability.
Question 4: Volume of distribution (Vd) is best defined as:
- The actual blood volume in the body
- The theoretical volume needed to contain all drug at the observed plasma concentration (Correct answer)
- The volume of urine produced per hour
- The volume of drug eliminated per unit time
Correct answer: The theoretical volume needed to contain all drug at the observed plasma concentration
Vd is a theoretical (apparent) volume that relates the total amount of drug in the body to the measured plasma concentration; it does not correspond to a real physiological volume.
Question 5: A drug with a high volume of distribution (Vd > 20 L/kg) is most likely:
- Confined primarily to the plasma compartment
- Highly protein-bound to albumin in plasma
- Extensively distributed to peripheral tissues (Correct answer)
- Rapidly eliminated by the kidneys
Correct answer: Extensively distributed to peripheral tissues
A high Vd indicates the drug distributes widely outside the plasma into peripheral tissues (e.g., fat, muscle), resulting in low plasma concentrations relative to total body drug.
Question 6: Which pharmacokinetic parameter describes the rate of drug elimination relative to drug concentration in plasma?
- Half-life
- Clearance (Correct answer)
- Volume of distribution
- Bioavailability
Correct answer: Clearance
Clearance (CL) is defined as the volume of plasma cleared of drug per unit time (mL/min or L/hr), and represents the body's efficiency at eliminating the drug.
Question 7: The elimination half-life (t½) of a drug is mathematically related to which two pharmacokinetic parameters?
- Bioavailability and protein binding
- Volume of distribution and clearance (Correct answer)
- Absorption rate constant and distribution rate
- Renal clearance and hepatic clearance only
Correct answer: Volume of distribution and clearance
t½ = (0.693 × Vd) / CL; half-life is directly proportional to volume of distribution and inversely proportional to clearance, so either change will alter half-life.
Pharmacy Pharmacokinetics 1
What does 'bioavailability' refer to in pharmacokinetics?