KAPS Pharmacokinetics and Biopharmaceutics 2 — Questions and Answers
Question 1: Which statement about first-order drug elimination kinetics is TRUE?
- The absolute amount of drug eliminated per unit time is constant
- A constant fraction of the drug present is eliminated per unit time (Correct answer)
- The elimination rate is independent of plasma concentration
- First-order kinetics only occur at very high drug concentrations
Correct answer: A constant fraction of the drug present is eliminated per unit time
In first-order kinetics, a constant fraction (percentage) of the remaining drug is eliminated per unit time, so the rate of elimination is proportional to the current plasma concentration.
Question 2: Drug clearance is BEST defined as:
- The fraction of drug excreted unchanged in urine
- The volume of plasma completely cleared of drug per unit time (Correct answer)
- The time required for plasma concentration to decrease by 50%
- The fraction of drug bound to plasma proteins
Correct answer: The volume of plasma completely cleared of drug per unit time
Clearance is the volume of plasma from which a drug is completely and irreversibly removed per unit time, typically expressed in mL/min or L/hr.
Question 3: Which equation correctly describes the relationship between elimination half-life (t½), volume of distribution (Vd), and clearance (Cl)?
- t½ = Vd × Cl / 0.693
- t½ = 0.693 × Vd / Cl (Correct answer)
- t½ = Cl / (0.693 × Vd)
- t½ = 0.693 × Cl × Vd
Correct answer: t½ = 0.693 × Vd / Cl
The equation t½ = 0.693 × Vd / Cl shows that half-life increases as the volume of distribution increases and decreases as clearance increases.
Question 4: Which pharmacokinetic parameter is MOST useful for comparing total drug exposure between different dosing regimens or formulations?
- Peak concentration (Cmax)
- Time to peak concentration (Tmax)
- Area under the plasma concentration-time curve (AUC) (Correct answer)
- Elimination half-life
Correct answer: Area under the plasma concentration-time curve (AUC)
The AUC represents total drug exposure over time and is the standard parameter used to compare bioavailability between different formulations or routes of administration.
Question 5: A drug has 25% oral bioavailability. If the desired IV dose is 80 mg, what approximate oral dose is needed to achieve equivalent systemic exposure?
- 20 mg
- 80 mg
- 160 mg
- 320 mg (Correct answer)
Correct answer: 320 mg
To achieve equivalent systemic exposure, divide the IV dose by the bioavailability fraction: 80 mg / 0.25 = 320 mg oral dose.
Question 6: The Biopharmaceutics Classification System (BCS) categorizes drugs based on which two properties?
- Molecular weight and charge
- Aqueous solubility and intestinal permeability (Correct answer)
- Protein binding and lipophilicity
- Half-life and volume of distribution
Correct answer: Aqueous solubility and intestinal permeability
The BCS classifies drugs into four classes (I–IV) based on aqueous solubility and intestinal membrane permeability, which are the key determinants of oral absorption and bioavailability.
Question 7: Steady-state plasma concentration is typically achieved after approximately how many half-lives of continuous dosing?
- 1–2 half-lives
- 2–3 half-lives
- 4–5 half-lives (Correct answer)
- 8–10 half-lives
Correct answer: 4–5 half-lives
Steady-state is reached after approximately 4–5 half-lives (~97% of true steady-state), at which point the rate of drug input equals the rate of elimination.
KAPS Pharmacokinetics and Biopharmaceutics 2
Which statement about first-order drug elimination kinetics is TRUE?